Calcium Supplement Absorption Myths and Realities

Calcium Supplement Absorption Myths and Realities

Calcium Supplement Absorption Myths and Realities

You have probably heard that calcium supplements are very hard to absorb, or not very bio-available. From different sources you may have heard the elderly with compromised digestion are only absorbing 2%, 4%, 10% or some other frightening low percentage. Usually the same marketers telling you about the low absorption of calcium carbonate are also offering the latest super calcium with "close to 100% absorption". Read on and you will be relieved to understand the science behind calcium absorption.

The Myth of Very Poor Calcium Absorption

This idea came from two places. First, some studies have shown calcium to be very poorly absorbed by individuals with low stomach acid when taken apart from a meal.

The other place this idea of low calcium absorption came from is the poor dissolution of some tablet forms. Carr and Shangraw showed some tablets where so closely bound with glues that they were taking 4 - 6 hours to dissolve! Since most food passes through your stomach in 3 hours, people have actually had calcium tablets appearing in their stool. Gelatin capsules are always preferable to tablets for this reason. The contents of gelatin capsules is a loose powder which has greater dissolution potential than a tightly bound tablet. Of course this is not a calcium absorption problem, but a poorly manufactured pill causing the low bio-availability.

If you think about it, a nutrient as important as calcium to human health could not be poorly accepted by our bodies. You will see that in the end, humans are well designed, and calcium can be absorbed in adequate amounts even by the elderly, if they are properly nourished.

The Myth of Very High Calcium Absorption

Usually the claims of a highly absorbed calcium, come from a confusion between solubility and absorption. The first step in breaking down your calcium supplement so that it is usable or bio-available is to dissolve it in your stomach. It is not uncommon for a calcium to be close to 100% soluble in either water or stomach acid. Here is where the confusion arises - solubility does not equal absorption. It is impossible for any calcium salt to be 100% absorbed through your intestinal wall and enter your bloodstream where it can be delivered to bone and other tissues for use.

The Strange Truth

Contrary to popular marketing claims, all calcium salts are relatively similar in absorption or bio-availability. All calcium salts bio-availability range from 23 - 37% if taken by normal subjects with food.(1) Taking out the few extreme study results which may even be in error, most calcium is within a few percentage points of 30% absorbed. You have heard that calcium citrate, for example has better absorption than calcium carbonate. Truth is, if they are taken with meals they are almost identical.

Some calciums like calcium citrate malate (CCM), and calcium bis-glycinate boast great solubility in water, but that does not equal significantly greater bio-availability. For example calcium bis-glycinate is 205 times more soluble in water than calcium citrate, yet only a little bit more bio-available.(2)

Top calcium expert, Professor Robert Heaney says "the solubility of a (calcium) source has very little influence on its absorbability.(3) Differences in solubility are of little importance, with calcium carbonate preparations, for example, being absorbed as well or better than some much more highly soluble salts. Gastric acid is not necessary for absorption of even poorly soluble preparations so long as they are taken with meals".(4) The take home lesson from Dr. Heaney is this - maximize the absorption of your calcium supplement by taking it with meals. That way your stomach has secreted adequate acid and this acid is present for long enough to ensure any form of calcium is dissolved and ready for proper absorption.


1. Journal of the American College of Nutrition, Vol. 19, No. 90002, 119S-136S (2000)
2. Life Extension Magazine, March 1999, William Faloon
3. Absorbability of calcium sources: the limited role of solubility. Heaney RP, Calcif Tissue Int. 1990 May.
4. Calcium supplements: Practical considerations. Heaney RP Osteoporosis International, Feb 1991.

This article was written for Algaecal Calcium Supplement