Magnesium Oxide Delivers More Magnesium with Far Fewer Pills

Blog / 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
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

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 from 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 from AlgaeCal


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 from 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 from 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 from 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.


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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