Your body contains more calcium -- about three pounds in the average adult -- than any other mineral. Nutritionist Elson Haas, M.D., states that 99 percent of your calcium stores are contained in your bones and teeth, while only 1 percent is found in your other tissues and your circulation. In addition to serving as a structural component in your skeleton, calcium plays vital roles in many other processes in your body. If you take a calcium supplement, its absorption can be influenced by a variety of factors.
Hormones
Maintaining your blood calcium level within a fairly narrow range is critically important for normal heart, nerve and muscle function. Your parathyroid glands, located behind the thyroid gland beneath your "Adam's apple," secrete parathyroid hormone, or PTH, whenever your blood calcium level falls. PTH stimulates the absorption of calcium from your intestine and the reabsorption of calcium from your kidneys. According to the Linus Pauling Institute at Oregon State University, vitamin D has similar effects on intestinal and kidney calcium absorption. The net effect of vitamin D and PTH activity is to increase your blood level of calcium. While you cannot control PTH secretion, taking sufficient vitamin D -- 600 to 800 IU for adults -- will improve calcium absorption.
Exercise
Calcium absorption typically parallels your body's need for this nutrient. Pregnancy, lactation and growth all increase calcium demands, and its absorption is enhanced in these situations. Likewise, exercise places stress on your bones, nerves and muscles, thereby augmenting your calcium requirements. Taking your calcium supplement shortly after exercise will improve its absorption, whether it is in chewable, liquid or tablet form.
Foods
The Linus Pauling Institute recommends taking most calcium supplements with food. However, Dr. Haas states that both calcium and magnesium are best absorbed in an acidic environment and that taking these supplements at bedtime or between meals is the best way to ensure optimal absorption. This is less of a concern with calcium citrate and calcium citrate malate supplements, which can be taken without regard to meal times. If you take a calcium carbonate supplement -- whether it is chewable or in some other form -- it will be better absorbed if taken on an empty stomach or with acidic foods, such as orange juice or citrus fruits.
What to Avoid
Calcium absorption is impaired by high-fat, high-phosphorus foods, such as red meats. Additionally, the phytic and oxalic acids found in some plant foods -- spinach, chard, beet greens, whole grains, cocoa and rhubarb, for example -- bind calcium in your intestine and prevent its absorption. Low stomach acid, which results from the use of antacids or ulcer medications, inhibits calcium absorption. If you use medications for ulcers or gastroesophageal reflux, take your calcium supplement several hours before or after taking the drug.
Considerations
Although it is better to obtain your calcium from food sources, many people do not consume enough dietary calcium to meet their needs. The use of calcium supplements to prevent osteoporosis is common practice. The chemical nature of your supplement has more influence on its absorption than whether it is a chewable, liquid or tablet preparation. Calcium carbonate is less absorbable than calcium citrate, citrate malate, aspartate or gluconate formulations. Most calcium supplements should be taken between meals or at bedtime, shortly after a workout.
References
- "Staying Healthy with Nutrition: Calcium"; Elson M. Haas, M.D.; 2006
- Linus Pauling Institute at Oregon State University: Calcium"
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