Calcium Absorption and Digestion
Whether or not the body has a sufficient supply of calcium depends not only on how much calcium is taken in, but also on how well it is digested and absorbed. One of the reasons why elderly people are especially prone to calcium deficiency is that the ability to absorb calcium declines with age. Children typically absorb 50-70% of the calcium they ingest, while an adult absorbs only 30-50%. The percentage might be even lower with older adults.
Vitamins A, C, and D and the minerals magnesium and boron all help make calcium absorption easier. Protein and fat, but not too much of either, are helpful as well. Milk is not only an excellent source of calcium, but a very reliable one since milk not only contains protein and fat, but also lactose, and all three components improve calcium absorption.
An acidic environment is more conducive to calcium absorption than an alkali environment. Therefore, most of the body’s absorption of this mineral takes place in the duodenum, where gastric hydrochloric acid helps move the process along.
Exercise and sunlight improve the digestion and absorption of calcium while stress inhibits it. The foods we also eat have a bearing on how well calcium is absorbed. Foods that are high in oxalic acid, like spinach, rhubarb, and chocolate, can make calcium absorption more difficult because they form insoluble salts in the gut. The phytic acid in whole grains and other fiber rich food can also interfere with calcium absorption, as can sugar and salt. Sometimes calcium is chelated with certain amino acids to make it more absorbable.
Because so many substances inhibit the absorption of calcium, anywhere from 30% to 80% of ingested calcium could wind up being excreted in the urine or feces. If calcium supplements are taken, in order to insure their maximum absorption, it is best to take them between meals or at bedtime when the stomach is more acidic. Supplements in the form of calcium citrate chelated to additives like Vitamin D3 and magnesium not only provide the benefit of the other nutrients, too, but are better tolerated by the stomach and more easily absorbed than supplements in the form of calcium carbonate.