Magnesium Oxide Delivers More Magnesium with Far Fewer Pills

Magnesium / Nutrition / January 20, 2017

Magnesium Oxide capsules zoomed in

It’s true that magnesium oxide is less soluble than several other forms of supplemental magnesium.

However, magnesium oxide is at least as effective (if not better) at restoring and maintaining a healthy level of magnesium in your cells and bones.

How is this possible? I’ll explain!

But before I do, we need to understand how magnesium is absorbed.

In all its natural forms, magnesium is bound to another chemical compound, for example: carbonate; gluconate; citrate; lactate; aspartate; or oxide. The combinations of magnesium and one of these compounds are called magnesium salts.

When you consume any magnesium salt, the magnesium must be freed from its partner compound during digestion and made soluble (ionized). Once it is made soluble, your body can absorb the magnesium.

For this to happen effectively, stomach acid has to be present. So it’s also helpful to remember that:

  1. It’s best to take your supplements with a meal because your stomach responds to your consumption of food by secreting stomach acid.
  2. Medications that prevent stomach acid production impair your ability to digest and absorb minerals – and virtually all other nutrients.

Why Magnesium Oxide Provides More Elemental Magnesium

It’s true that magnesium oxide is not as easy to render soluble as some other magnesium salts. It’s therefore not absorbed as rapidly as other forms of magnesium, e.g. magnesium citrate, gluconate, lactate, aspartate.

But although magnesium oxide has a lower rate of absorption it contains a MUCH greater amount of actual magnesium to begin with. More than what is provided by other magnesium salts.

Therefore, even with the lower rate of absorption, magnesium oxide still delivers more magnesium per tablet.  So more magnesium gets into your bloodstream to deliver all its many benefits to your bones and body!

This is illustrated in the table Comparison of Magnesium Salts below: 1-2

Comparison of Magnesium Salts
MG Salt % Elemental MG % Elemental MG Absorbed Mg’s of Elemental MG Absorbed per 100 mg of MG Salt
Oxide 60% 23%* 13.8
Carbonate 28% ~20% ** ~5.2
Chloride 26% 20% 5.2
L-lactate 12% 42% 5
Citrate 11% 30% 3.3
Aspartate 8% 42% 3.3
Glycinate 14% 23% 3.2
Gluconate 6% 19% 1.14

*On the web, you’ll see many sites claiming that only 4% of the magnesium in magnesium oxide is absorbed. This claim is based upon a small study by Firoz et al. (2001), which is discussed fully below. The actual data in this study shows something very different.  The stated percentage of elemental magnesium absorbed from magnesium oxide in the above table — 23% — is the statistic provided in a review and meta-analysis of numerous studies by Ranade et al., (2001), cited below.  

**Magnesium carbonate is nearly insoluble, but in the presence of stomach acid (HCl), magnesium carbonate is converted into magnesium chloride, which allows 20% of elemental magnesium to be absorbed.

As you can see, magnesium oxide contains the most elemental magnesium of 60%. And 23% of this can be absorbed.

Magnesium citrate, for example, contains only 11% elemental magnesium. And only 30% of this is absorbed.

So the percentage of elemental magnesium to begin with is just as important as the rate of absorption.

What Does This Mean For You, In Practical Terms?

You can get comparable or better health benefits with magnesium oxide. And you’ll also require fewer capsules, which will save you time and money.

The research most often cited to disparage magnesium oxide is a small study by Firoz et al. of 16 volunteers. The aim of this study was to test the claim that organic (chelated) magnesium salts (e.g., aspartate, lactate) are more easily absorbed than non-organic salts (e.g., oxide, chloride).3

The 16 volunteers were given four commercially-available magnesium salts: 2 organic (aspartate, lactate) and 2 non-organic (oxide, chloride), after which the amount of magnesium in their urine was checked. More magnesium excreted in the urine is thought to indicate that more magnesium has been absorbed; less magnesium excreted is thought to indicate that less magnesium has been absorbed. This rationale is based on the principle that the body works hard to maintain a steady state of magnesium balance, and in a steady state of magnesium balance, any extra magnesium absorbed will be excreted in the urine.

In this study, those taking magnesium oxide excreted less magnesium on average. So magnesium oxide was said to have a low fractional absorption rate of 4%. However, there are 2 important points not shared in this study:

  1. Half of the volunteers in this study excreted more or very comparable amounts of magnesium when taking magnesium oxide as they did when taking the other magnesium salts. Take a look for yourself at the table below – Urinary Magnesium, mg/day. The data in the following table is taken directly from Firoz M, et al’s 2001 article in Magnesium Research.

Averaging out the data produces a result that does not reflect what actually happened in the participants. Yet, what was reported is repeatedly cited on the internet. This is why I always read the full paper of any study I am going to rely upon for information.

    2. Most importantly, the key practical discovery made in this study was: “Magnesium excretion increased with all magnesium supplements.”  What this means is that all the magnesium salts tested, including magnesium oxide, delivered more magnesium than was needed to meet the body’s magnesium balance requirement.

Urinary Magnesium, mg/day
Study participant MG oxide MG chloride MG aspartate MG lactate Control 1* Control 2*
A 100 156 95 114 77 70
B 95 43 78 65 68 43
C 101 89 103 137 75 32
D 66 120 137 161 100 103
E 78 166 101 119 134 65
F 63 144 88 48 56 67
G 84 78 76 67 74 61
H 142 182 214 198 128 129
I 78 39 55 62 102 60
J 114 112 110 76 53 86
K 77 106 177 116 80 32
L 114 94 137 117 109 92
M 66 87 51 81 104 115
N 82 82 82 163 76 85
O 162 133 85 106 75 75
p 34 120 58 87 28 57

*Controls did not receive any supplemental magnesium.

Magnesium Oxide is Effectively Absorbed

Despite what you may have read on various websites, the peer-reviewed research on PubMed shows that magnesium oxide is effectively absorbed:

In a study involving 18 men, 24 hours after consumption of magnesium oxide supplements, magnesium levels in the urine increased about two times the normal amount.  And, after 48 hours, magnesium levels had increased to roughly four times normal. The conclusion drawn by the researchers: these results clearly show that “magnesium oxide is effectively absorbed and elevates the biologically-active levels of magnesium in the bloodstream.” 4

It’s important to note here that magnesium oxide did not increase urinary excretion of magnesium within a couple of hours. This is an important point which I’ll explain below in “Higher bioavailability does not translate to more effective delivery to tissues.”

All forms of magnesium salts used in animal studies have been found to effectively restore magnesium levels in magnesium-depleted animals.

In one such study in 2005, rats were first given a magnesium-depleted diet and then provided with the same diet supplemented with 10 different magnesium salts: magnesium oxide, chloride, sulfate, carbonate, acetate, picolate, citrate, gluconate, lactate or aspartate. The results showed that while magnesium absorption values varied from 50% to 67%, all the magnesium salts used were equally efficient in restoring magnesium levels.5

The researchers also noted that “the quantity of magnesium in the digestive tract is the major factor controlling the amount of magnesium absorbed.” And as you now know, magnesium oxide contains a far greater amount of elemental magnesium than any of the other magnesium salts .5

A more recent animal study confirmed and strengthened these findings. In this one, for 5 weeks, rats were fed one of eight test diets supplemented with phytic acid (5 g/kg diet) and magnesium (155 mg elemental Mg/kg diet) from the following magnesium salts: magnesium oxide; magnesium sulfate; magnesium chloride; magnesium citrate; magnesium gluconate; magnesium orotate; and magnesium malate or EDTA magnesium salt.

The addition of phytic acid to the animals’ diet is important because phytic acid binds strongly to minerals and forms an insoluble complex. This means less of the minerals consumed can be absorbed. Despite the addition of phytic acid to the animals’ diet, all the magnesium salts tested were found to be comparably bioavailable: “The results indicate that any differences in the magnesium bioavailability of the compounds were small and physiologically irrelevant.” 6

woman put effervescent tablet in glass

Higher Bioavailability Does Not Necessarily Translate to More Effective Delivery to Tissues

When a magnesium supplement is highly bioavailable, it will be rapidly absorbed from the small intestine into the bloodstream, and magnesium blood levels will quickly rise. This sounds good, but when blood magnesium levels exceed a critical threshold, the excess is rapidly excreted by the kidneys. The end result is a shorter duration of magnesium availability to tissues.  Magnesium salts with the greatest water solubility, bioavailability and rate of absorption are also more rapidly excreted in urine.

The lower parts of the small intestine are the primary sites of magnesium absorption. However, magnesium is also absorbed throughout the entire intestinal tract. Magnesium does not have special carriers that pull it into the bloodstream. Its absorption is a passive transcellular process.

For this kind of absorption process, the quantity of magnesium that passes through the digestive tract is the major factor controlling the amount of magnesium that is absorbed. 

Because magnesium oxide contains more elemental magnesium and is less soluble, it’s absorbed into the bloodstream more slowly as it passes through the digestive tract. It will not raise blood levels excessively, and will therefore not be rapidly excreted. 5,7.8

The Research-Backed Bottom Line on Magnesium Oxide

You can get the same benefits from magnesium oxide with fewer pills. Magnesium oxide is the most effective magnesium supplement – and that is why it was selected for use in AlgaeCal Plus.


    1. Molecular weights: For the other magnesium salts, replace oxide with the name of salt desired.
    2. Ranade VV, Somberg JC. Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humans. Am J Ther. 2001 Sep-Oct;8(5):345-57. PMID: 11550076
    3. Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001 Dec;14(4):257-62. PMID: 11794633
    4. Altura BT, Wilimzig C, Trnovec T, et al. Comparative effects of a Mg-enriched diet and different orally administered magnesium oxide preparations on ionized Mg, Mg metabolism and electrolytes in serum of human volunteers. J Am Coll Nutr. 1994 Oct;13(5):447-54. PMID: 7836622
    5. Coudray C, Rambeau M, Feillet-Coudray C, et al. Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach. Magnes Res. 2005 Dec;18(4):215-23. PMID: 16548135
    6. Bertinato J, Plouffe LJ, Lavergne C, et al. Bioavailability of magnesium from inorganic and organic compounds is similar in rats fed a high phytic acid diet. Magnes Res. 2014 Oct-Dec;27(4):175-85. doi: 10.1684/mrh.2014.0374. PMID: 25635418
    7. Ranade VV, Somberg JC. Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humans. Am J Ther. 2001 Sep-Oct;8(5):345-57. PMID: 11550076
    8. Musso CG. Magnesium metabolism in health and disease. Int Urol Nephrol. 2009;41(2):357-62. doi: 10.1007/s11255-009-9548-7. Epub 2009 Mar 10. PMID: 19274487

Author: Lara Pizzorno, MDIV, MA, LMT


I know this is an old thread but I found it very interesting and switched to Mag Oxide. Now I have a new but related question.

I have become very interested in adding silica to my diet for anti-aging. Have read dozens of studies about silica bioavailability. They all say that the various forms of silica tend to have a lot of bioavailability problems.

Is it valid to measure bioavailability by urinary excretion? All the studies do this. Could urinary excretion be something undesirable? I want the silica to stay in my body and feed my joints and skin, not be excreted in urine.

The studies always say that Silicon Dioxide powder is minimally bioavailable or not bioavailable at all. And the best bioavailability is from Orthosilicic Acid. Again, they are making these conclusions based on the amount of the substances that are excreted in urine. Is this perhaps totally wrong-headed?

Is it possible we have a similar situation as with Magnesium Oxide? And in fact, Silicon Dioxide will get absorbed and made available to the cells, perhaps more slowly than other forms? But better overall?

I hope Lara is still around and can address this question. Thanks.

Lara Pizzorno
Lara Pizzorno

Unfortunately, the “state of the art” in regards to evaluating how much of a mineral is effectively used in the body before excretion is far from optimal.

Apparent absorption is determined using fecal or urinary excretion, and values are usually expressed as a percentage of intake.
Here’s the formula used:
Apparent absorption = intake – (total fecal excretion – total endogenous fecal excretion) divided by intake x 100
Urine is a major pathway of excretion for some minerals – including silicon as well as magnesium, iodine and potassium – but a minor pathway for others such as manganese, iron, zinc and copper.

Collecting urine during absorption studies allows net retention to be calculated, but probably has little value in determining bioavailability of a mineral element. In many situations, the mineral element excreted in the urine represents a portion that was potentially nutritionally effective and has been involved in, or was available for use in, metabolism. In such cases, it’s an error to include the urinary fraction as a part of the unavailable portion of total dietary intake.

Functional assays for bioavailability are a better option but rarely used in consumer testing. In a functional assay, the level or activity of an essential compound in which the mineral element is a necessary component (e.g., iron for hemoglobin and cobalt for vitamin B12) are used. Measurements in tissues of selenium-dependent glutathione peroxidase levels and cytochrome C oxidase activity as influenced by copper have been used as indicators for bioavailability of these two elements. I don’t see anything similar for silicon.

However, it is true that our kidneys eliminate minerals that are either (1) not in a bioavailable form (for example, are bound to phytate or, in the case of silicon, is not soluble in water, so is not bioavailable [as I think you know orthosilicic acid is the form of silicon that is soluble in water]) or (2) when we have consumed more of the mineral than can be absorbed at one time because all the mechanisms utilized for its absorption are saturated. An example here is calcium, whose fractional absorption rate drops when more than 500 mg is consumed at one time. Or strontium, which we do not absorb when consumed at the same time as calcium because both minerals use the same absorption pathways, and calcium is always preferentially absorbed over strontium, so saturates all available transporters.


Thanks so much, Lara, for your very informative reply.

I remember reading in one of the studies that urinary excretion is justified as a measure of nutrient bioavailability on the assumption that the body seeks equilibrium and so will dump excess nutrients in the urine. In some studies I saw, more silicon was excreted than was ingested in a few cases.

If urinary excretion is a measure of the body’s seeking equilibrium, then there’s no point in taking high dose supplements because you just lose them in the urine, as the body doesn’t need them.

But is it possible that the scientists have it completely wrong, and the opposite is the truth? That the forms of silicon or magnesium that produce the LEAST amount of urinary excretion are, in fact, the MOST bioavailable? Because the nutrient stays in the body and is not excreted into the toilet?

They say there’s an inverse relationship with silicon content and absorption in most foods — banana has a lot of silicon but very little is measured in urine, so it is presumed to have low bioavailability. Other foods have very little silicon but apparent high absorption rates. If very little of banana silicon is eliminated in the urine, where does it go? Maybe it goes to the joints, skin and other areas that need it?

From what you said, if you want the nutrient to stay in your body and not be excreted, is it reasonable to take smaller doses throughout the day, instead of a large amount all at once?

I saw at least one reference that silicon dioxide powder CAN be absorbed if you add it to water.

From EFSA, “Calcium silicate and silicon dioxide/silicic acid gel added for
nutritional purposes to food supplements: Scientific Opinion of the Panel on Food Additives and Nutrient Sources added to Food.”

“No data have been submitted on the bioavailability of silicon from either silicon dioxide or silicic acid gel. However, several studies have shown that silicon present under similar form was readily available from foods and in many cases showed absorption similar to that of silicon from liquids. Furthermore, given the conversion of silicon dioxide/silicic acid to orthosilicic acid upon hydration, and the bioavailability of silicon from orthosilicic acid, the Panel considers that silicon from silicon dioxide/ silicic acid gel is bioavailable.“

And another from EFSA, “Re-evaluation of silicon dioxide (E 551) as a food additive”
in EFSA Journal 16(1) · January 2018

From abstract: “Silicon dioxide appears to be poorly absorbed. However, silicon-containing material (in some cases presumed to be silicon dioxide) was found in some tissues….”

“Some studies reported that less than 0.5% of silicon orally applied as silicon dioxide (1,250 mg) was excreted via urine but urinary silicon was always within the range of normal physiological variation”

I also saw one study that said SiO2 in nano form might cause intestinal problems.

I also am not sure if what they are referring to is Si02 powder in its crystalline form or amorphous Si02 or Si02 gel.

Do you have any thoughts on the best sources of bioavailable silica? I’ve been drinking bamboo leaf tea and eating bamboo shoots and non-alcoholic beer but I’m interested in the most efficient way to get large therapeutic amounts of Si into my body in order to discover if it’s a fountain of youth :o)

If Silicon Dioxide is in fact bioavailable to a limited extent, it is far easier, and cheaper, to buy AR grade Silicon Dioxide powder and steep it in a jug of drinking water, maybe for an extended time.

When I added Magnesium Oxide powder to drinking water, it tended to form crystals. But maybe some of it was absorbed in the water. I crunched the crystals with my teeth and ate them. I have no idea how much was absorbed.

Thanks again for sharing your knowledge and opinions.


I’m 66 and take between 1.5g and 2g of magnesium oxide per day before bed as a laxative. I am chronically constipated and would not like to be without this. I currently don’t supplement calcium, but from what I read here I guess you would advise it. I am a little concerned about taking calcium as I have read it can deposit on artery walls. As I am taking a magnesium “bolus” do you think 400mg calcium/day would do?

Megan AlgaeCal
Megan AlgaeCal

Hi Paul, thanks for reaching out!

If you have osteoporosis or osteopenia, or would simply like to maintain bone health, AlgaeCal may be for you! AlgaeCal is different from most calcium supplements because it’s natural, plant-based, and does not cause calcium deposits in soft tissues such as your arteries. We added in vitamin K2 which helps transport calcium away from organs and into your bones! The safety of AlgaeCal is demonstrated in our 3 human clinical studies here.

Paul, we would recommend checking in with your doctor about the right amount of calcium for you. Keep in mind that each capsule of AlgaeCal provides around 88mg of magnesium. Many of our customers find it helpful to share this information sheet with their doctors.

If you have any questions after your doctor’s appointment, feel free to reach out! ?

-Megan @ AlgaeCal


Thanks for the reply, it was very helpful.

It seems that I’ve been under a misapprension with regard to magnesium intake. For RDA, I read that to mean that I need to absorb 420mg daily. It appears that this is incorrect and it actually means I need to ingest 420mg daily.

That being the case, there will no doubt be much variation in absorption of magnesium depending on which form a person takes. It also makes the using of RDAs virtually redundant due to large variations in absorption rates of the type of magnesium that was used.

I would appear that this subject is far more complicated than I first thought.


Just tried to edit my last comment, but no provision unfortunately.

Only noticed the spelling error after posting. I meant to write ‘misapprehension’ rather than what I did write.


This is all extremely useful information with regard to magnesium intake.

One thing I find perplexing is the RDA which is quoted as being 420mg for someone like me, and I’m wondering how I can ever take enough to attain this RDA level.

With the low amount of Mg being absorbed by all the forms, it seems unlikely that I will ever achieve my 420mg daily target.

If you have any comments on this, I would be very interested to read them.

Blaire AlgaeCal
Blaire AlgaeCal

Hello David! Our bone health advisor who wrote this article and author of the book “Your Bones,” Lara Pizzorno, has responded to your query. You can find her response below ?

“Hi David,
Great question! Thanks for taking the time to write in. The 420 mg RDA does not refer to the amount of magnesium actually absorbed, but to the amount ingested. More importantly, the RDA is too low – it should be 600 mg/day since we need 1,200 mg of calcium, and the correct ratio between Calcium:Magnesium is 2:1. This amount can easily be met using magnesium oxide, which as you know, contains the most elemental magnesium of any supplemental form and is the form of magnesium AlgaeCal Plus contains, providing 360 mg per day. In addition to this, you need to rely (for so many reasons!) on a healthy diet for the remaining 240 mg of magnesium you need each day! If you have a copy of Your Bones, you can use the Foods Rich in Magnesium table to get a quick estimate of the amount of magnesium YOUR diet is providing for you. You can check this book out from any public library if you don’t wish to own a copy. And here’s a link to the World’s Healthiest Foods information of magnesium, which includes a list of the foods that contain the most magnesium for the lowest amount of calories per serving. Pumpkin seeds are an especially good choice for men as they are also an excellent source of zinc, which plays key roles in prostate health and function.

Hope that helps. Let us know if you have any further questions!

– Blaire @ AlgaeCal

Joel Bórquez
Joel Bórquez

Great article, i dind´t know of this page, but sure i will visit it from now.

Megan AlgaeCal
Megan AlgaeCal

Thank you for your kind words, Joel!

We’re so glad you liked the article and hope you continue to enjoy the recipes, nutrition information, and exercises on our blog ?

If you have any questions, don’t hesitate to give our Bone Health Consultants a call at 1-800-820-0184!

-Megan @ AlgaeCal


Im confused as to the dosages implied from this article.

Dietary magnesium absorption ranges from around 40-50% I believe,

400mg is the approximate RDA for men, which yields a max of 200mg absorbed magnesium, assuming you reach the 400mg all from diet.

My 4.2g scoop of magnesium citrate powder provies around 600mg elemental magnesium, and the label states this as 150% of the RDA.

This 150% figure would only be correct if we assumed that the absorption of magnesium from its citrate salt falls in the same 40-50% range that is found in dietary magnesium. But, your chart clearly shows its 30%. So that 150% figure is inflated.

My question is, is the RDA on supplements simply the amount of magnesium present, and fails to take into account the absorption rate of that specific salt compared to the standard absorption rate of diet?

Lara Pizzorno
Lara Pizzorno

Hi Yoda,

Great questions! Thanks.

First, yes, the recommended dose that is listed on a supplement bottle is only how much elemental magnesium is present (I believe you meant the recommended dose on the product label, not the RDA?) and does not reflect the absorption rate or bioavailability of the type of magnesium salt provided.

Regarding RDA, the RDAs for magnesium (420 mg /d for men and 320 mg/d for women ) do not properly balance the RDA for calcium, which is 1,000 mg per day for men up to age 70, then 1,200 mg per day for men as well as for women (and a number of recent papers have recommended up to 1,500 mg per day in postmenopausal women with bone loss issues).

The optimal balance between calcium and magnesium is 2:1. So, we require 600 – 750 mg of magnesium daily – and possibly more if we are chronically stressed or exercise regularly at sufficient intensity to sweat vigorously (or live somewhere hot, like Arizona or Florida) because chronic stress or sweating will increase the rate at which we eliminate magnesium. Sweating, however, is really good for us – clears toxins!

You mention your 4.2g scoop of magnesium citrate powder provides ~ 600mg of elemental magnesium, which sounds excellent. The only problem here is the issue I tried to explain in this post, which is that when a bolus dose of magnesium is provided, most of it will be rapidly cleared from the bloodstream by the kidneys and eliminated in urine. This would certainly be the case with 600 mg of elemental magnesium from magnesium citrate since citrate rapidly disassociates from magnesium in the stomach even without the presence of stomach acid.

The goal is not just immediate bioavailability (how rapidly magnesium – or any water-soluble nutrient – is released and absorbed into the bloodstream), but magnesium’s release in smaller amounts over a longer period of time, thus maximizing our ability to use it effectively. If you do need additional magnesium, you might consider taking 1/3 of a scoop of your magnesium citrate powder at a time and spacing your doses out over the course of your day.

However, you should know that consumption of too much magnesium can be harmful. The research shows that high intake of total calcium or magnesium only reduces risk of colorectal cancer when the Ca/Mg ratio is in the 2:1 range – a little higher is OK, but a lot higher is not OK. In other research — using data from the Women’s Health Initiative studies — excess magnesium in relation to calcium appeared to be detrimental to bone and increased fracture risk of the forearm and wrist. In China, where people tend to consume more magnesium and less calcium (they eat more vegetables, no dairy), consuming excessive amounts of magnesium actually increased risks of all-cause mortality and mortality due to CVD and colorectal cancer among women.

The take-away here is that “more,” particularly in the case of supplements, is not always better! Remember, if you are taking AlgaeCal Plus, the full 4 capsule dose is giving you 720 mg of calcium properly balanced by 360 mg of magnesium in the form of magnesium oxide. Also, you’re taking a divided dose (2 capsules AM and 2 PM), so you are maximizing your ability to effectively use both the calcium and magnesium provided. To reach 1,200 mg of calcium / 600 mg of magnesium daily, your diet should be providing you with the remaining 480 mg of calcium and 240 mg of magnesium – unless you feel you have symptoms suggestive of magnesium insufficiency. In that case, you may want to ask your doctor about running an RBC (red blood cell) magnesium to check your status and supplementing with additional magnesium (or eating more magnesium-rich foods) if indicated.

Regarding your comment about the amounts of magnesium in the chart — they are taken from research carefully evaluating and comparing the absorption rates among different magnesium salts, so I believe these amounts are more accurate than a generalization made in relation to dietary magnesium.

Re dietary magnesium, a couple of additional factors to consider: The magnesium present in our foods is embedded in the matrix of whichever magnesium-rich food is being consumed. How much of it will be available, much less absorbed, depends on other factors present in the food (for example, its content of phytates and fiber), plus the digestive function of the person consuming the food. Here, a key question is whether this person is producing sufficient stomach acid. As you probably know, our ability to secrete stomach acid typically drops off as we age, plus many individuals now take acid blockers [e.g., PPIs, H2 blockers, OTC antacids), and/or suffer from infection with Helicobacter pylori, which interferes with stomach acid production, and its presence is extremely common. If all these potential issues weren’t troublesome enough, many of us have food allergies/sensitivities or dysbiosis that harms the lining of the digestive tract, promoting “leaky gut,” and that impairs nutrient absorption.

Hope this helps. Be well!



Thanks for this. A couple of years ago, my doctor recommended magnesium to help with my restless legs. I had been buying magnesium oxide, without paying any attention to forms of magnesium.

After reading several articles saying magnesium oxide was the least bioavailable form, I bought magnesium gluconate. My restless legs returned. So, I tried chelated magnesium. Honestly, my legs were causing such insomnia that I was barely functioning.

A few days ago, I happened upon your article. It confirmed what I had begun to suspect. So, I rushed out and bought a bottle of magnesium oxide. I’ve slept like a baby the last 3 nights.

I’ve learned an important lesson about believing everything I read on the internet. I should have trusted my own experience. But I’m also glad to have found your confirmation. Thanks so much for your research, and for making it public.

Megan AlgaeCal
Megan AlgaeCal

Hi Lisa!

Thank you so much for taking the time to share your story! We’re so happy to hear that you are now sleeping like a baby ? It gives us great joy to hear that our articles are helping others – feel free to browse through some of our other articles here if you’d like!

-Megan @ AlgaeCal

Yuri Davidovsky
Yuri Davidovsky

An excellent article, far the best I have ever read on magnesium, lays out thing very clearly, logically and in an easy to understand fashion, something that many scientific papers are sorely lacking, unfortunately.

However, there appears to be an error in the ‘Comparison of Magnesium Salts’ table, the elemental content of magnesium citrate should be 16%, rather than 11%, I can verify it by looking at supplement packaging on my desk, 1830mg of citrate contains 295.7mg of the element. The table at the bottom of this article also confirms it:

Also the “Elemental MG Absorbed per 100 mg of MG Salt” value should be corrected upward from 3.3mg. From the 295.7mg at 30% absorption rate 88.75mg of Mg would be taken up, this would make it 88.75 / 18.3 = 4.85mg. Values for oxide appear to be correct in the table.


This makes sense if one is DIY’ing their magnesium.

Most of-the-shelf supplements deliver a specific amount magnesium, explicitly stated on the packaging e.g, 400mg elemental magnesium in 2 tablets.

It’s worth noting this distinction, as assuming otherwise might have people taking 6X more than they need (in the case of Glycinate). Using the above example of 400mg per 2 tablets, this equates to 12 table which is a whopping 2.4grams of magnesium. Enough to make people quite sick.


What are your thoughts on the relatively new sucrosomal (liposomal) magnesium? I found a study which shows very good absorption even compared to mag oxide.

Lara Pizzorno
Lara Pizzorno

Hi Michael,

Thanks for sharing this interesting study with me! This product may be helpful for you.

Here’s my review of the study:

As you may have noted, sucrosomial magnesium is magnesium oxide to which sucrose esters have been added in an attempt to increase absorption/bioavailability.

You may also have noted that this it was a very small study – just 10 participants whose average age was 34. And they excluded from the study anyone with “history of bone diseases, diabetes mellitus, chronic fatigue syndrome, premenstrual symptoms, peptic ulcer, intestinal resection, inflammatory disease of the gastrointestinal tract, malabsorption/maldigestion, hypertension, gall bladder disease or any other relevant medical condition; current chronic medication intake; history or current abuse of drugs, medication or alcohol, or intake >2 alcoholic beverages/day; known hypersensitivity to study product or any ingredient in the preparation” – so, in sum, we have 10 young healthy study participants with good digestion and ability to absorb minerals.

Look at Table 1 – you’ll see that magnesium oxide concentrations compare very favorably with those of sucrosomial magnesium in the blood and in red blood cells (RBC is, as you know a far better indicator of magnesium uptake and actual use than blood/serum). The place where the difference in concentration is noticeable is urine – which is a marker of magnesium’s elimination from the body, not its absorption into and use in our cells. RBC is the best indicator for our effective use of magnesium.

The box plot diagrams make it look like sucrosomial magnesium is more effective because they are comparing initial concentration to 24 hours later, and magnesium oxide concentrations were higher initially than those of sucrosomial magnesium, so I found that a bit misleading for readers who are not used to evaluating research papers.

Also, it seems strange to me that they stress how much more sucrosomial magnesium was found in urine since what this most likely shows is that absorption occurred so rapidly that the body’s pathways for moving the bolus of magnesium that was absorbed from the intestines into our cells became saturated, so far more sucrosomial magnesium was excreted.

Despite all this – the sucrosomial magnesium product appears to be safe and might be helpful for you. If you can access this product, why not give it a try and see how you feel?

Hoping you find it helpful,


David Abner
David Abner

By this same reasoning, shouldn’t magnesium sulfate also be a cost effective it’s supplement? 1 gram of epsom salt contains 100mg elemental magnesium, and it’s well below the laxative threshold. Plus an 8lbs pound bag (3,630 grams) can be found at Walmart for $5. Thoughts?

Tom White
Tom White

Also, I wanted to ask about how much daily magnesium supplementation I need to take to reach the RDA for my age group.

I am 29 years old.

The RDA for Magnesium for a 29 year old male is 400mg, as stated at the weblink below:

If I am taking a magnesium supplement which provides 400mg of Magnesium Citrate per day, does that mean I have met my RDA for that day?

Or do I need to take 400mg of actual elemental magnesium and then factor in the amount that is absorbed, as stated in your article?

According to your article, 400mg of Magnesium Citrate per day would only give me 13.2mg of magnesium that is actually absorbed (using the figures in the comparison table).

Does that mean I need to take 30 times more magnesium citrate in order to get 400mg of magnesium that is actually absorbed?

I look forward to your reply and thank you in advance

Warmest regards,

Tom White.

Lara Pizzorno
Lara Pizzorno

Hi Tom,

Sorry it has taken me some time to get back to you – please accept my apologies. I’ve just been maxed!

Since you are dealing with numerous intestinal pathogens, many of which love citrate and use it as a favorite food source, I suggest you switch from magnesium citrate to another magnesium salt.

The one that may work best for you is magnesium hydroxide. This is the magnesium salt used as a laxative in Milk of Magnesia. It’s used as a laxative because hydroxide ions are very effective at attracting and retaining water in the intestines, which increases peristalsis and evacuation of the bowel. So, although magnesium hydroxide increases potential for diarrhea in most folks, in your case, it may be the most beneficial form.

Magnesium hydroxide is 42% elemental magnesium and has a bioavailability of 15%. You can compare this to the other forms of magnesium in the table in this article. I did not include magnesium hydroxide in this article because of its laxative effects, but again, in your case, it may be just what you need. The label on the supplement you purchase should specify how much elemental magnesium is present in the dose of magnesium hydroxide it provides.…/magnesium_hydroxide…

Given the complexity of the issues you are dealing with, if you have not already had the OAT run (Organic Acids Test offered by Great Plains Lab), I suggest you discuss having this done with your doctor(s). A few weeks ago, I taped an #AskLara on the OAT, which you can access on The AlgaeCal Community – just enter #AskLara OAT in the search box on the left hand side of the page.

Lastly, if you could possibly include the amounts of calcium, D3, K2 and zinc that are present in AlgaeCal Plus as part of the dosages of each that you need to take, I hope you will consider starting AlgaeCal Plus as soon as possible because it will also be giving you several forms of plant-derived calcium, plus magnesium oxide (which you can read more about it my post on AlgaeCal), plus boron, plus a wide array of trace minerals (including excellent amounts of silicon and some zinc (30.1 mcg/g of zinc. The full dose of AlgaeCal Plus contains 2.4 grams, which means it contains 72.24 mcg of zinc – not tons, as I expect you are taking at least 30 mg/d but still potentially helpful.

Do keep me posted on how you are doing,



Tom White
Tom White

Dear Lara,

Thank you for writing this helpful and valuable article.

I am currently consuming a very low carbohydrate diet due to my personal health conditions (which include candida overgrowth, Blastocystis Hominis parasite infection, Bacterial dysbiosis, mould allergy and many food allergies and intolerances). I am working with my practitioners to help improve these conditions.

However, this limited diet means that my fibre intake is low and my diet is currently an organic foods diet which is a high fat, moderate protein and low carb diet consisting of hemp seed powder, barley grass powder, coconut cream, and grass fed butter or ghee.

Therefore I take Magnesium supplements to improve bowel regularity and eliminate mild constipation on this relatively “low fibre” diet.

I cannot eat or chew any food because I have TMJ disorder (jaw joint osteoarthritis) and therefore eating or chewing is very painful. I blend all of my food or used pre-ground organic foods from the health food shop (e.g. hemp powder rather than hemp seeds).

I currently take 12ml of Nutricology Magnesium Chloride per day spread out evenly throughout the day in my drinking water, which helps with regularity and also reduces my TMJ pain.

I also take 2 tablets of NOW Magnesium Citrate 200mg per day (one with breakfast, one with dinner). This product also helps with the bowel regularity and reducing my TMJ symptoms.

I want to continue with the Nutricology magnesium chloride but perhaps try a different product rather than the NOW magnesium citrate to see if I can experience even further benefits.

If you were me, which product on the market would you take as a stand alone magnesium supplement? If you would take magnesium oxide, which specific product would you take? I am not asking you to officially recommend a product but if you can suggest a product, that would be very helpful for me because my current bottle of NOW magnesium citrate will run out in 3 days.

Also, I cannot currently take AlgaeCal because I need to individually manage and adjust my dosages of Calcium, Vitamin D3, K2 and Zinc to help with my other health conditions.

I look forward to your reply and thank you in advance

Warmest regards,

Tom White.


Unless I am much mistaken, the expansive comment on forms of magnesium Lara wrote on Jan 31, 2017 contains a glaring error. When describing the amount of magnesium in magnesium glycinate she says that it is 14% — a number I confirmed elsewhere. She then goes on to say this translates to 4.8mg in a 150mg capsule. By my math 14% of 150mg is 21mg or over four times as much as the 4.8mg stated — and twice as much as magnesium threonate which she compares it to. Am I missing something?

Lara Pizzorno
Lara Pizzorno

Hi Geoff,

Yes, you are not factoring in the impact of the 3rd column in the table — % of Elemental Mg Absorbed. Magnesium glycinate is 14% elemental magnesium, but only ~23% of that 14% is actually absorbed. So, 150 mg x 14% does = 21, but then you have to take 23% of 21, which = 4.8 mg, and this is the amount of elemental magnesium actually absorbed when a 150 mg capsule is consumed. Thanks for asking for clarification!

Be well, Lara

Michal W
Michal W

Hi Lara,

Your info about Mg oxide was shock to me. It seems I’ve been victim of this myth too. Anyway, you encouraged me to try this form myself.

But I have question regarding B6 and P5P
By accident I found P5P (25 mg sublingual) to be effective for my withdrawal symptom from antidepressant cocktail: tension that ends with fury (I have to kick and shout; never had this in my life before).

My B6 is actually HIGH (2x times the norm; I checked it about the same time but was expecting the opposite).
This didn’t seem to make sense to me as a layman until I found some statement that it’s because B6 is not absorbed and is just circulating in the blood?
There’s only one place I found it, so I treated it with caution.

Can you shed some light or give some references where I could read?
I know P5P works! The problem is that not always – sometimes like a charm and sometimes just a bit or nothing (been using it for a few months).

Since about a week I am experimenting with Mg lactate (120 mg of free Mg, 3x/day) and also found it helps sometimes for my tension.

I am taking Mg (lactate)
– morning and evening as routine 120 mg
– when tension hits (i.e. every day) 120 – 180 mg
Does it seem good routine? Or would it be better to take only during tension but higher amounts?

It’s all (Mg – P5P, B6 – P5P connections) very important as now I have not only depression with severe strange somatizations but also withdrawal symptoms.

Lara Pizzorno
Lara Pizzorno

Hi Michal,

Since P5P helps and B6 levels are elevated, I believe your genetic inheritance includes SNPs in the enzyme responsible for converting B6 to P5P that render this enzyme ineffective, and render you unable to effectively make this conversion. By taking B6, you will not be providing the P5P required for methylation. Dysfunctional methylation – specifically a dysfunctional COMT enzyme — can compromise clearance of stress hormones, producing tension, anxiety and depression. Methylation requires the activated forms of not just B6, but also folate, B12 and riboflavin. I suggest you try taking B Active (the BioClinic Naturals product we use that provides all the Bs in activated forms), which may help a lot. Also, you should have your 23&me genomic profile run, so you can access your raw data and have it analyzed to confirm which SNPs you have in, not only B6 but all the B vitamins, that might compromise their activation and thus your methylation capacity.

Re magnesium, low intake of magnesium definitely promotes depression and anxiety;

But I was unable to find any papers specifically stating that magnesium lactate is more effective than other forms. If you are not experiencing loose bowels from taking the amounts of magnesium lactate you mention, then it should be fine for you. If you are hypochlorhydric (produce little stomach acid), you may find magnesium citrate is even more helpful since this magnesium salt will disassociate without stomach acid. One caveat here – your intake of magnesium should be in balance with that of calcium. The ratio between them should be 2:1, calcium: magnesium.

Hope this helps, please keep me posted and don’t hesitate to write back with further questions,

Be well, Lara

Andrew Letourneau
Andrew Letourneau

I have been informed by a friend that magnesium salts/oils are all the rage. How do they get absorbed into the bloodstream? That is, how is the elemantal magnesium separated from the binder to be of use? Does the first table still apply?

Jenna AlgaeCal
Jenna AlgaeCal

Hi Andrew,

Lara Pizzorno explains how magnesium is absorbed near the bottom of the article (second last section)!

“The lower parts of the small intestine are the primary sites of magnesium absorption. However, magnesium is also absorbed throughout the entire intestinal tract. Magnesium does not have special carriers that pull it into the bloodstream. Its absorption is a passive transcellular process.

For this kind of absorption process, the quantity of magnesium that passes through the digestive tract is the major factor controlling the amount of magnesium that is absorbed.”

– Jenna @ AlgaeCal


I just purchased a Droughtmaster Traveler 10 that makes drinking water from humidity. The water is from my greenhouse. Water is glacial and sweet and is doing amazing things physically, but has no Magnesium. Was researching Prill…magnesium oxide to treat the water and found your statement. Thank You! The pH is 6.5 from the device but will it alkalize further with magnesium oxide?

Jenna AlgaeCal
Jenna AlgaeCal

Very interesting, Mary! Our expertise is specific to bone health, and we’re sorry we aren’t very familiar with the effects of magnesium oxide being used with a water generator.

Hopefully the company you purchased from would have some insight and we highly recommend contacting them for their best suggestions! 🙂

– Jenna @ AlgaeCal



“Magnesium oxide was virtually insoluble in water and only 43% soluble in simulated peak acid secretion (24.2 mEq hydrochloric acid/300 ml). Magnesium citrate had high solubility even in water (55%) and was substantially more soluble than magnesium oxide in all states of acid secretion. Reprecipitation of magnesium citrate and magnesium oxide did not occur when the filtrates from the solubility studies were titrated to pH 6 and 7 to stimulate pancreatic bicarbonate secretion. Approximately 65% of magnesium citrate was complexed as soluble magnesium citrate, whereas magnesium complexation was not present in the magnesium oxide system.”

Jenna AlgaeCal
Jenna AlgaeCal

Hi Ed,

Thanks for commenting! For a full review of the different forms of magnesium supported with numerous references please read Lara’s post above (there’s lots of valuable information in the comments below too).

– Jenna @ AlgaeCal


Lara, great information! I have been looking into optimizing my magnesium intake. I am looking at various products, and am also considering creating my own magnesium bicarbonate using magnesium hydroxide powder and carbonated water. Where does this form/method fit into the scale of effectiveness?

Jenna AlgaeCal
Jenna AlgaeCal

Hi Ken,

After reaching out to Lara with your question, she suggests checking out her reply to Deborah which includes magnesium hydroxide in a list of comparisons.

Lara also suggests taking 25 mg P5P along with your magnesium drink. For more information on P5P, please see her response to Gaetane’s comment 🙂

– Jenna @ AlgaeCal


I like this article. But what are your thoughts on strontium? You guys have a Strontium supplement that contains 680 mg.


Jenna AlgaeCal
Jenna AlgaeCal

Hi Isaiah,

Lara has written extensively on the research behind strontium – including the different forms and optimal bone-building dosage of 680 mg. You can read it by clicking here!

– Jenna @ AlgaeCal


Now that’s proper research.
Finally someone explaining it appropriately instead of just parroting what others say.

Thank you


I just ordered AlgaeCal Plus and Strontium Boost. I have been taking the Jigsaw bran of sustained release magnesium supplements which is in the form of Dimagnesium Malate. Where does that fit in with the various forms of magnesium?

Thank you!

Lara Pizzorno
Lara Pizzorno

Hi Deborah,

Despite the wonderful sounding claims made by Jigsaw, no published research confirms any of them. I did a thorough search (Pub Med, Google Scholar, Science Direct) and could not find a single paper providing evidence of any of these claims – the only paper I saw in which Mg malate was evaluated was conducted in 1995 and suggested that Mg malate may be helpful for fibromyalgia. No follow up studies were conducted. (Here’s the citation for that: Russell IJ, Michalek JE, Flechas JD, Abraham GE. Treatment of fibromyalgia syndrome with Super Malic: a randomized, double blind, placebo controlled, crossover pilot study. J Rheumatol. 1995 May;22(5):953-8. PMID: 8587088). The “source” given in support of Jigsaw’s claims is another promotional article, not an article published in a medical journal.

So, I don’t know how magnesium malate compares to other forms of magnesium. What I could find was information on the amount of elemental magnesium in Mg malate compared to other forms – copying this in here – supposedly this info was taken from NIH website, but I’m not sure it’s accurate for the other forms, know it is not accurate for Mg oxide. Note that this source continues to cite the urban myth that Mg oxide has only 4% bioavailability – see my article for full explanation of why this is incorrect – bioavailability is actually 23% for Mg oxide.

Anyway, here’s what I was able to find re Mg malate compared to other Mg salts:

Magnesium Sulfate —> Elemental Mag = 10%, Bioavailability = ?
Magnesium Chloride —> Elemental Mag = 12%, Bioavailability = ?
Magnesium Oxide —> Elemental Mag = 60%, Bioavailability = 4%
Magnesium Carbonate —> Elemental Mag = 45%, Bioavailability = 30%
Magnesium Hydroxide —> Elemental Mag = 42%, Bioavailability = ?
Magnesium Citrate —> Elemental Mag = 16%, Bioavailability = 90%
Magnesium Lactate —> Elemental Mag = 12%, Bioavailability = 99%
Magnesium Glycinate —> Elemental Mag = 18%, Bioavailability = 80%
Magnesium Malate —> Elemental Mag = 6.5%, Bioavailability = ?
Magnesium Taurate —> Elemental Mag = 9%, Bioavailability = ?

Also note, on Jigsaw’s promotional page, they make a big deal of their SRT (slow release technology) saying that slow release avoids digestive issues (they’re referring to osmotic diarrhea here). Mag oxide NATURALLY is released slowly. If taking this product feels effective for you, then great! If you want to confirm efficacy, I suggest having an RBC magnesium lab test run – I discuss this lab in the Labs Appendix in Your Bones, 2nd ed.

Wendy Nevatt-Dakan
Wendy Nevatt-Dakan

I am taking plant based magnesium aquamin seawater 500mg, since I am on the basic algaecal and am supplementing. Where does that fit?


Hi Wendy,

The optimal ratio of calcium to magnesium is 2:1. If you are taking 3 capsules per day of AlgaeCal Basic that gives you 750 mg of magnesium and 65 mg of magnesium. If you are taking additional magnesium, then it would be recommended to try and get as close to the 2:1 ratio as possible, unless your doctor or naturopath has recommended otherwise.

– Monica @ AlgaeCal


I haven been taken algaeCal and Strontium Boost for 3 months and I realize that one of this pill is making my vowel movement very soft. Perhaps too much magnesium? Or something else ? Please. Advise me what to do.
Since then my vowel movements are not normal, they are only when I stop taken for few days.


Hi Connie,

Thanks for sharing. Magnesium is a natural laxative, so if you are taking an additional magnesium supplement, this may be why your bowel (I’m guessing that’s what you meant by vowel) movements have been soft. AlgaeCal Plus is formulated with the optimal 2:1 calcium to magnesium ratio for both absorption and bone health – so if you are getting more magnesium than calcium through your diet this may also be the reason. If you’d like to call in and speak with one of our Bone Health Advisors we can dig in more as to why this may be happening (there could be other factors as well). You can call us Canada and USA toll free at 1-800-820-0184 from Monday through Friday: 6am to 4pm (PST)
and Saturday & Sunday: 8am to 2pm (PST).

– Monica @ AlgaeCal


With Mag. Oxide, my vowel’s are consonant! .


I thought this was a very interesting and enlightening article. Would this apply to magnesium glycinate as well and magnesium threonate? My understanding is that mag. threonate crosses the blood brain barrier.


Hi Judy,

Lara discusses glycinate and its elemental magnesium and absorption briefly in the first table of the post. She’s currently working on a writing project and is unavailable at the moment, but I’ll be sure to reach out and try and get a response to your question when she becomes available again.

– Monica @ AlgaeCal


Hi Judy,

Lara has written an in-depth response on magnesium glycinate and threonate in reply to Gaetane’s question above. It should also answer yours as well.

– Monica @ AlgaeCal

Georgiana Yasko
Georgiana Yasko

Thank you for the education!

Gaetane White
Gaetane White

I take magnesium glycinate that is easily absorbed because it is carried to your cells bound to the amino acids, along with Biomed BoneSure, a plant based calcium. I am not convinced from the above argument for magnesium oxide but I would be interested in hearing your comments comparing the two magnesiums. I feel the above argument is based on someone with adequate stomach acid and no problems with the laxative effect found with most magnesium. Thank you.


Hi Gaetane,

Yes, Biomed BoneSure actually uses AlgaeCal calcium, which is stated on their label. Lara is currently in the middle of a writing project, but I’ll be sure to reach out to her for a response to your glycinate comment when she becomes available again.

– Monica @ AlgaeCal

Lara Pizzorno
Lara Pizzorno

Hi Gaetane,

Monica let me know about your question and I’ve been busy working on some new articles so sorry I’m just getting to this now.
First, thanks for your great questions. Unfortunately, the internet is loaded with “myth-information.” This is why I always read the full medical journal articles and don’t even trust the abstracts, much less the way findings are reported to the public, particularly by those with a vested financial interest in finding a “selling” point for a product.

Regarding magnesium absorption

Regardless of whatever type of magnesium salt is consumed (with ONE possible, but as yet unproven exception discussed below), during digestion, the magnesium will be disassociated from its stabilizing partner. This will happen regardless of whether the partner is an amino acid like glycine or an organic acid like citrate or an element like oxide. This separation of magnesium from its partner releases magnesium in its ionized form, which is the form in which magnesium is absorbed, and the primary form in which it circulates in the bloodstream.

FYI – “chelated” is a buzz word used to sell certain types of magnesium supplements. It simply means “bound to a Krebs cycle intermediate,” i.e., that the magnesium salt partner is a Krebs cycle intermediate, such as citrate, glycinate, etc. Yes, these forms are more quickly bioavailable. No, that does not equal “optimal.” The Krebs cycle intermediates, like glycinate and citrate, are more easily detached from the elemental magnesium contained (more soluble), freeing this magnesium for absorption more rapidly, but they are detached before the magnesium is absorbed. The magnesium in magnesium glycinate is not absorbed intact and delivered to your cells.

Glycine is a non-essential amino acid – the simplest of all the amino acids. It’s a non-essential amino acid because our bodies make it and use it to produce many types of proteins, including purines. Purines are used to make adenine and guanine, two of the five two of the five bases in nucleic acids that make up our DNA and RNA, and are also key components in other important biomolecules, including the energy currency of the body, ATP. The point here is that your body has many uses for the glycine chelated to magnesium in a magnesium glycinate supplement. This glycine will be disassociated during digestion, and although some may later combine with free magnesium in the bloodstream, most will be utilized for other purposes. In sum, glycine has no impact on our absorption of magnesium — other than that glycine is easily disassociated from magnesium, quickly freeing the magnesium for absorption, mainly in the lower parts of the small intestine, with small amounts absorbed in the colon.

The same is true for all the other forms of magnesium salts – with one possible exception: magnesium threonate. Cell and animal studies indicate that magnesium threonate crosses the blood brain barrier, increases intracellular concentrations of magnesium in the central nervous system, and has a number of beneficial effects on neuronal plasticity.

Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010 Jan 28;65(2):165-77. doi: 10.1016/j.neuron.2009.12.026. PMID: 20152124
Sun Q, Weinger JG, Mao F, et al. Regulation of structural and functional synapse density by L-threonate through modulation of intraneuronal magnesium concentration. Neuropharmacology. 2016 Sep;108:426-39. doi: 10.1016/j.neuropharm.2016.05.006. Epub 2016 May 10. PMID: 27178134

Whether the magnesium threonate complex is absorbed intact from the digestive tract into the bloodstream is not known. Most of the magnesium in the bloodstream (~55 to as much as 80%) remains in its free, ionized form (specifically, this form is a cation, which is an ion that is missing one or more electrons and therefore has a positive charge; cations are almost always minerals with a positive charge). About 33% of the free, ionized magnesium absorbed from the digestive tract binds to proteins in the bloodstream, and about 12% of it gets complexed with anions, which are typically chemicals that are negatively charged. Threonate is one such anion.

Nutrient Metabolism, Structures, Functions and Genes, ed. Kohlmeier M, 2nd ed. , Academic Press, Elsevier, 2015, p. 745
Magnesium in Laboratory Evaluations for Integrative and Functional Medicine, 2nd ed, Ed. Lord RS, Bralley JA. Metametrix Intitute, Duluth, GA, 2008, pp. 84-85.

Threonate is a small sugar molecule naturally produced in our bodies. It’s formed as a result of our metabolism of vitamin C – specifically, by the spontaneous conversion of the product of ascorbic acid oxidation (which is called dehydroascorbic acid [DHA]), into oxalic acid and threonic acid (aka threonate).

Threonate can definitely bind to free magnesium in the bloodstream, and the resulting complex can be carried into the brain by glucose transporters (GLUTs), which transport sugars (monosaccharides) and other small carbon compounds into the brain via passive facilitated transport.

Or magnesium L-threonate might be absorbed intact directly from the digestive tract into the bloodstream and then carried into the brain by GLUTs. We don’t know.
What we do know from the animal research is that supplementation with magnesium L-threonate resulted in increased intracellular Mg+ levels in the cerebrospinal spinal fluid. Because of magnesium’s critical importance for healthy brain function, these promising results are being investigated as a potential means of helping to maintain healthy brain function and to prevent cognitive decline and Alzheimer’s.
What the animal research has not shown is that magnesium L-threonate was absorbed intact from the digestive tract and delivered to the brain. It’s entirely possible that the large amount of threonate consumed when magnesium L-threonate was given was first separated from the magnesium in the digestive tract, but later combined with it in the bloodstream, and the resulting magnesium L-threonate complex made its way to the brain.

Furthermore, other research suggests that threonate, in the form of calcium L-threonate might be helpful for bone, but only if threonate exerts additional effects on osteoblasts and/or osteoclasts since calcium threonate is not as well absorbed as calcium carbonate. L-theanine’s fractional calcium absorption rate is 26.49 ± 9.39 %. Wang H, Hu P, Jiang J., 2013. Calcium bioavailability of calcium L-threonate in healthy Chinese subjects measured with stable isotopes ((4)(4)Ca and (4)(2)Ca).Eur. J. Clin. Pharmacol. 69, 1121e1126 Eur J Clin Pharmacol. 2013 May;69(5):1121-6. doi: 10.1007/s00228-012-1420-5. Epub 2012 Nov 16. PMID: 23229796 In comparison, the fractional absorption rate of calcium carbonate is 39 +/-0.7. Martin BR, Weaver CM, Heaney RP, et al. Calcium absorption from three salts and CaSO(4)-fortified bread in premenopausal women. J Agric Food Chem. 2002 Jun 19;50(13):3874-6. PMID: 12059174

To date, all we have to support added benefit from calcium L-threonate is one in vitro (test tube) study of rabbit osteoclasts that were treated with sodium L-threonate, calcium L-threonate or calcium gluconate. Both sodium L-threonate and calcium L-threonate lowered the bone resorption activity of rabbit osteoclasts, but calcium L-theonate did a better job of it – and calcium gluconate was ineffective. He JH, Tong NW, Li HQ, et al. [Effects of L-threonate on bone resorption by osteoclasts in vitro]. [Article in Chinese] Sichuan Da Xue Xue Bao Yi Xue Ban. 2005 Mar;36(2):225-8. PMID: 15807273

In sum

All of the above does suggest that the organic anion, threonate, has beneficial effects on magnesium utilization in the brain. After much searching, I was finally able to find out how much elemental magnesium is present in a magnesium threonate supplement. It was not easy to discover, which makes sense because it is not much: 2,000 mg worth of magnesium threonate contains 140 mg of elemental magnesium, which translates to a 150 mg capsule delivering ~10.7 mg of magnesium.

Back to magnesium glycinate

Magnesium glycinate did not show superior bioavailability to the other Krebs cycle intermediates in the extensive review of the PubMed research I conducted when I wrote the Magnesium Oxide post.
And even if magnesium glycinate had shown better bioavailability, remember, a fast, high rate of absorption is not necessarily optimal. What matters most is the amount of magnesium in the magnesium salt. If you take a supplement containing 150 mg of a magnesium salt that actually provides just 10 mg of elemental magnesium (e.g., Magnesium threonate, for example, see below), and you quickly absorb all the magnesium from it, you get less benefit than if you take a 150 mg supplement of a magnesium salt that contains 80 mg of elemental magnesium that you absorb slowly. Not only will you be getting far less elemental magnesium in the first salt, but you will excrete more of it if it’s bioavailability causes blood levels to quickly increase and reach a level higher than that our bodies rigorously maintain in the bloodstream. Magnesium glycinate is 14% elemental magnesium, which translates to 4.8 mg of magnesium per 150 mg capsule – even less magnesium than is provided by magnesium L-threonate.

Regarding magnesium’s “laxative effect”

The carrier for magnesium into our cells is the activated form of B6, which is called pyridoxal-5-phosphate (P5P). A fairly large percentage of the population has inherited SNPs (single nucleotide polymorphisms) that render the enzymes that convert B6 to P5P very slow / much less active – including yours truly, which is why I take P5P along with AlgaeCal Plus. I discovered this in a roundabout way when I began taking sufficient vitamin D3 for my needs, which increased my ability to absorb calcium – and also increased my needs for magnesium. A possible topic for another post.
Here the key point is that if taking magnesium is resulting in diarrhea, this may indicate P5P is needed or more magnesium is being consumed than the body can absorb. 25 mg of P5P taken along with any supplement that provides magnesium should be very helpful – and P5P is quite safe and inexpensive. Also, many supplements contain magnesium – anyone who is experiencing loose stools should check ALL the supplements being taken and add up how much supplemental magnesium overall is being consumed. It could just be that much more magnesium is being taken than realized.

I remember about 10 years ago, a patient of my husband’s (Dr. Joe Pizzorno) came to us with severe migraines. He was a high-level business man under a great deal of chronic stress, so magnesium was suggested. (Stress causes increased loss of magnesium.) His migraines went away, but after a couple of years, he developed explosive diarrhea. First, we had him add up all the magnesium he was taking from all the supplements he used, plus his meal replacement drink mixes – and it turned out to be a staggering amount! He cut back on the amount of magnesium he was consuming, and the diarrhea immediately stopped — but even though he was still getting plenty of magnesium, his migraines came back. Research showing a high incidence of SNPs that result in slow conversion of B6 to P5P was just coming out, and if you cannot convert B6 to P5P effectively, you cannot get magnesium into your cells, so I suggested P5P. Within days, he had no more migraines and no more diarrhea, and he has been fine since.

I suggest you consider a trial of 25 mg of P5P taken when you take any magnesium supplement. Below are the citations for a couple of the most recent papers underscoring the importance of B6 for our ability to utilize magnesium. But, given the number of individuals who cannot effectively convert B6 into P5P, the form in which it gets magnesium into our cells, P5P is the best choice (I also wrote about this in Your Bones, 2nd ed., pp. 231-2).

Spasov AA, Lezgitsa IN, Kharitonova MV, et al. [Effect of some organic and inorganic magnesium salts on lipoprotein state in rats fed with magnesium-deficient diet]. [Article in Russian] Eksp Klin Farmakol. 2008 Jul-Aug;71(4):35-40. PMID: 18819439
Spasov AA, Petrov VI, Iezhitsa IN, et al. [Comparative study of magnesium salts bioavailability in rats fed a magnesium-deficient diet]. [Article in Russian] Vestn Ross Akad Med Nauk. 2010;(2):29-37.PMID: 20364677

Thanks again, Gaetane. I hope this information will be helpful to you.

Shameer Mulji
Shameer Mulji

“I suggest you consider a trial of 25 mg of P5P taken when you take any magnesium supplement.”

Should P5P be taken during the same meal as magnesium or will taking it during separate meals yield the same result?

Blaire AlgaeCal
Blaire AlgaeCal

Hi Shameer,

Good question! It is best to take P5P at the same time as when you take magnesium.

Let us know if you have any further questions ?

– Blaire @ AlgaeCal


I use Gly mag as I have read it is the best absorbance. So I am annoyed at this whole different list of magnesium traits and uses. It’s like the cereal isle in the supermarket.

Jenna AlgaeCal
Jenna AlgaeCal

Hi Joyce,

Thank you for taking the time to comment, we truly appreciate your feedback. You’re right, shopping for magnesium can feel like browsing the cereal aisle in the supermarket! This is why Lara reviewed the latest research to help our readers better understand the different forms of magnesium & make informed decisions when purchasing! In regards to magnesium glycinate specifically, Lara discusses it in-depth in her response just above this comment. We hope this is helpful, Joyce!

– Jenna @ AlgaeCal

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