Calcium Supplements and Osteoporosis

Barbara Sax
Published Online: Monday, December 1, 2003
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    Osteoporosis is a major health threat in the United States, particularly among people older than 50 years of age. Estimates indicate that 10 million Americans have osteoporosis, and another 34 million are at risk of developing osteoporosis due to low bone mass.

    Although women are more at risk of developing the condition (80% of patients with osteoporosis are women), all people older than 50 should be concerned about prevention, because studies indicate that 55% of Americans older than 40 exhibit signs of low bone mass.

    The best way to fight osteoporosis is with early intervention - ideally in the form of a calcium-rich diet and weightbearing exercise. Men younger than 65 and premenopausal women should be getting 1000 mg of calcium a day, and men and women aged 65 and older should be getting a daily dose of 1500 mg.

    The problem is that most people do not consume a diet of the dairy products, leafy green vegetables, fish, and tofu that delivers adequate levels of calcium. Thus, many patients are turning to calcium-fortified foods and calcium supplements to fill their calcium gap.

An Abundance of Choices

    With so many calcium products filling pharmacy shelves, it can be difficult for patients to choose a supplement that fits their needs. The National Osteoporosis Foundation recommends that patients avoid calcium that is derived from bone meal, dolomite, or unrefined oyster shells because these substances may contain lead or other toxic metals.

    Calcium comes from many sources and in many forms. Calcium carbonate (the type found in chewable antacids such as Tums and in Os-Cal) is the most common and has the highest concentration of calcium by weight (40%). Calcium phosphate contains 38%, and calcium citrate contains 21% calcium. Because calcium citrate does not require gastric acid for absorption, it is a better choice for those patients who have limited gastric production. Calcium lactate contains 13% elemental calcium, and calcium phosphate contains 9%.

    Using these percentages, the amount of elemental calcium in supplements can be calculated as follows: One 500-mg tablet of calcium citrate contains 105 mg of elemental calcium (500 mg x 0.21 [21%]).

    Calcium citrate malate is yet another form of the mineral. It is 10% to 20% better absorbed than other forms, but because it has less elemental calcium in each tablet, patients have to take more of it to get the same benefit of, say, calcium carbonate.

    Solubility influences the bioavailability of calcium from supplements, and not all calcium supplements are equally soluble. The rate of dissolution of many supplements varies from 33% to 75%. Adequate solubility of a tablet can be tested by placing a tablet in a glass of warm water or vinegar to determine if it dissolves within 30 minutes.

    Dr. Bess Dawson-Hughes, professor of medicine and the director of the bone metabolism laboratory at the USDA?s Nutrition Center on Aging at Tufts University, said that it matters little which form of calcium supplements patients take as long as they take them correctly. Because the body can handle only about 500 mg of calcium at any given time, calcium should be delivered throughout the day in those amounts. ?There?s also a benefit to taking supplements at bedtime,? said Dr. Dawson-Hughes.

    It is important that pharmacists caution patients against taking too much calcium. Although a daily dose of up to 2000 mg of calcium appears safe for most people, chronic high intake can cause adverse side effects, such as constipation. High intake of calcium can also interfere with the absorption of other essential nutrients, such as iron and zinc.

    Vitamin D helps the body absorb calcium. Calcium products, such as Viactiv, which combine calcium and vitamin D in a single supplement, can be effective in boosting absorption of calcium. Patients must take care not to exceed their recommended daily dosage of vitamin D, however, because, when taken in excess, the vitamin can become toxic. Patients should not take more than 800 IU/day of vitamin D unless prescribed by a physician.



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