Calcium Supplements & Absorption

Calcium is the most abundant mineral in the human body. Dr. Elson Haas, author of "Staying Healthy with Nutrition," states that 98 percent of your body's calcium is sequestered in your bones, but the remaining 2 percent exerts profound influences on how your cells, tissues and organs function. A variety of factors can affect the absorption of calcium from your intestine, such as vitamin D levels, the composition of your diet and the nature of the calcium itself.

Vitamin D Aids Calcium Absorption

Vitamin D, or calciferol, is known as the "sunshine vitamin" because it can be synthesized in your skin during exposure to ultraviolet light. Vitamin D improves the absorption of calcium from your gut, decreases the excretion of calcium from your kidneys and stimulates the release of calcium from your bones. Vitamin D is present in some foods, such as oily fish, egg yolks and butter and can be consumed as a supplement. A minimal daily dose of around 400 IU is recommended for most adults, with 1,000 to 2,000 IU advised for optimal health.

Dietary Composition Affects Calcium Absorption

A 2010 report in "Critical Reviews in Clinical Laboratory Sciences" reveals that scientists still do not fully understand the mechanisms of intestinal calcium absorption; however, they do know dietary factors influence calcium absorption. Absorption is enhanced by certain amino acids, such as lysine and glycine, a small amount of dietary fat, and an acid environment. Calcium absorption is impaired by high-fat or high-protein diets, excessive phosphorous, which occurs with the frequent consumption of meat, and dietary oxalates and phytates that are found in leafy greens and whole grains.

Calcium Supplements

Some of the most commonly used calcium supplements are also the most poorly absorbed. These supplements, which include oyster shell, bone meal, dolomite or other forms of calcium carbonate, are typically cheaper than better-absorbed preparations, and, according to Haas, physicians often recommend them without considering their poor bioavailability. Calcium lactate is somewhat better-absorbed than calcium carbonate. Calcium citrate and amino acid chelates, such as calcium aspartate or glycinate, are probably the most widely available and best-absorbed forms of calcium supplements. Calcium orotate has gained a reputation as the most bioavailable and physiologically useful form of calcium, but this claim has been contested by such experts as Andrew Weil, M.D. In addition, calcium orotate is expensive and more difficult to find.

Considerations and Recommendations

Adequate calcium intake is essential for normal cellular function and the maintenance of good bone strength. Adult males and premenopausal women should consume 500 to 1,000 mg of calcium daily from all sources, including foods and supplements. Postmenopausal women should get 1,200 to 1,500 mg daily. Not all calcium supplements are equal, with chelated forms offering better bioavailability. Calcium is better absorbed if taken on an empty stomach, but some forms, such as the chelates, may be adequately absorbed even when taken with food.