You hear a lot about it in the marketing for various forms of calcium but does it really differ among various types of calcium?Actually the answer is no. Many papers have clearly demonstrated that the various forms of calcium are all comparably bioavailable when calcium supplements are taken with a meal and even with a snack. There reason for this is that most forms of calcium require an acidic environment in the stomach to be what is considered solubilized. Which simply means that the elemental calcium is disassociated from its carrier molecules so that it’s ready to be absorbed. When we eat a meal or a snack, our stomachs automatically create hydrochloric acid so we can digest our food and solubilize the minerals within it or supplements that we take. You may have heard that calcium citrate is more bioavailable than other forms of calcium. Well, it’s simply not true. What is true, is that the calcium will disassociate from the citrate even if no stomach acid is present, but once it’s removed from its binding carrier molecule all forms of calcium are equally well absorbed. Where did this myth that calcium citrate was more bioavailable originate? It actually dates back to a single study back in 1985 in which calcium citrate was found to be better absorbed than calcium carbonate under fasting conditions in 11 elderly subjects who were achlorhydric which means they did not produce stomach acid. What is not reported in the findings of this 1985 study is that when these elderly subjects who weren’t producing stomach acid when they were fasting, were given calcium supplements along with breakfast, the calcium was well absorbed and calcium citrate was no more bioavailable than any other form of calcium. To quote from this paper “ Administration of calcium carbonate as part of a normal breakfast, resulted in completely normal absorption even in achlorhydric subjects. These results indicate that calcium absorption is impaired in achlorhydria in fasting conditions and that is all the results indicate – they do not indicate that calcium citrate is magically more bioavailable than other forms of calcium. And more recent studies have confirmed this. The 1985 study published in the New England Journal of Medicine (I’ll provide the citations to these comments if you want to look at it) More recent studies that confirm this include a study in the Journal of the American College of Nutrition in 2001 that looked at the bioavailability of various forms of calcium in 24 postmenopausal women and it found that in all forms that they tested, produced identical 24 hour time increases in blood levels of calcium. In other words, calcium from any of the calcium sources was equally well absorbed and had equivalent bioavailability. In yet another study that was conducted in 2002 published in the American Journal of Clinical Nutrition. Researchers tested elderly subjects and they found that calcium was equally bioavailable from skim milk, calcium carbonate, and orange juice fortified with calcium citrate. Again, it did not make a difference. And what’s the point here? Well, with very few exceptions, which we’ll talk about in the next study – calcium bioavailability is just not an issue. It’s a marketing issue, but not a health issue. So in the next video, I will talk to you about the few times where there might be an exception where you should be talking to your doctor about which form of calcium supplements to take. I hope this was helpful to you and I will see you next time.
Recker RR. Calcium absorption and achlorhydria. N Engl J Med. 1985 Jul 11;313(2):70-3. PMID: 4000241
Heaney RP, Dowell MS, Bierman J, et al. Absorbability and cost effectiveness in calcium supplementation. J Am Coll Nutr. 2001 Jun;20(3):239-46. PMID: 11444420
Martini L, Wood RJ. Relative bioavailability of calcium-rich dietary sources in the elderly.Am J Clin Nutr. 2002 Dec;76(6):1345-50.PMID: 12450902 in Straub DA. Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutr Clin Pract. 2007 Jun;22(3):286-96. PMID: 17507729