 Calcium SupplementsWhile the fortification of foods with calcium is a public health approach to increasing calcium intake, the use of calcium supplements is an individual, and for the most part, self-directed approach. Because intake of calcium supplements is mainly self-directed, a number of concerns have been raised regarding their use. A critical question is whether or not intake of calcium supplements is necessary. And if so, which calcium supplement is the best for the particular individual? Other issues include the safety and cost of calcium supplements. Concern about dietary supplements in general recently resulted in new FDA regulations for both nutrition labeling and health claims for dietary supplements. Effective July 1995, labels for dietary supplements of calcium (and other dietary supplements) must provide the same basic nutritional information as found on the labels of nearly all conventional foods. The new rules also authorize health claims for calcium and osteoporosis on dietary supplements, effective July 1994. The demand for calcium supplements is reflected by retail sales data. In 1993, calcium supplements accounted for 6.7% of total supplement sales or $245 million a year in the U.S.. Between 1991 and 1994, sales for calcium supplements increased 30%. Reasons why individuals take calcium supplements are varied and include: concerns about the adequacy of the calcium content of their diets; misconceptions that calcium sources such as dairy foods increase fat intake and promote undesirable weight gain; perceived or actual milk protein allergy/lactose intolerance; and a desire to provide insurance against calcium deficiency or to treat or prevent disease. According to a recent review of calcium preparations, there are at least a dozen common calcium preparations and hundreds of different formulations available. Calcium carbonate is the most common preparation; some others include tricalcium phosphate, dicalcium phosphate, bone meal, calcium citrate-malate, oyster shell, calcium lactate, and calcium gluconate. These calcium preparations differ in a variety of ways. Calcium carbonate has the highest concentration of calcium by weight (40%), whereas calcium citrate has 21% calcium and calcium phosphate has 8% calcium by weight. Although calcium carbonate has the highest concentration of calcium by weight, this form of calcium is relatively insoluble, especially at a neutral pH. In contrast, calcium citrate, although containing about half as much calcium by weight, is a more soluble form of calcium. Because calcium citrate does not require gastric acid for absorption, it is a better choice for patients with achlorhydria (i.e., limited gastric acid production). In addition to the amount (dosage) of calcium in various supplements, the solubility and absorption of calcium must be considered. In general, there are not large differences in the absorption of calcium from different calcium supplements or foods. However, the solubility of calcium supplement preparations needs to be considered. Prior to absorption, calcium preparations must dissociate into elemental calcium. The more soluble a calcium supplement product is in vitro (i.e., measured by the ability to dissolve in 6 ounces of vinegar within 30 minutes), the more soluble the calcium preparation is in the body. Because of better manufacturing processes, name brand supplements may be more bioavailable than generic products. While dosage and solubility can influence the bioavailability of calcium from calcium supplements, the timing of intake and meal conditions also are important. Calcium from supplements appears to be more efficiently absorbed when consumed in divided doses, each containing less than 500 mg of elemental calcium. The NIH Consensus Conference recommends consuming calcium supplements between meals to increase calcium bioavailabilty. The long-term safety of consuming large doses of single nutrients including calcium is of concern. Although calcium intakes up to 2,000 mg/day appear to be safe for most individuals, potential adverse effects can occur as a result of chronic high intakes or intakes of specific calcium preparations. Potential adverse effects include gastrointestinal problems such as constipation. Certain preparations of calcium (e.g., bone meal, dolomite) may contain contaminants such as lead, aluminum, arsenic, mercury, and cadmium. Significant amounts were identified in calcium carbonate supplements labeled oyster shell or natural source. Chronic intake of these supplements may pose an unnecessary risk. Most commercial calcium preparations are tested for heavy metal contamination. High intakes of calcium supplements may interfere with the absorption of other nutrients such as iron and zinc. Intake of calcium supplements also may interfere with the absorption of concurrently consumed medications, and vice versa. Other potential adverse effects of chronic intakes of high doses of calcium include milk-alkali syndrome (ectopic calcium deposition), hypervitaminosis D (i.e., in the case of supplements containing calcium and vitamin D), and possible hypercalciuria leading to kidney stone formation. However, recent studies indicate that increased intake of calcium does not increase risk of kidney stones. Moreover, restricting dietary calcium may increase urinary excretion of oxalate which in turn increases risk of kidney stones. Cost among various calcium supplements differs widely. According to a recent review of 15 different calcium preparations, wholesale cost ranged from $1.20 to almost $60.00 for a one month supply of 1,000 mg calcium/day. Despite these differences, no clear evidence of increased benefit appears to exist among the various preparations. For certain individuals who cannot meet their calcium needs from foods, calcium supplements are warranted. However as reviewed above, a number of factors influence the choice of calcium preparation. Individuals who need calcium supplements should choose one that contains a relatively high percentage of elemental calcium by weight, disintegrates readily, provides a form of calcium that is bioavailable and inexpensive, is manufactured by a reputable pharmaceutical company, and is free of toxicants. In general, absorption of calcium is most efficient when the supplement is consumed in doses of 500 mg or less. Intake of calcium supplements with vitamin D should be limited because of the risk for vitamin D toxicity. Source: Dairy Council Digest, January/February 1995, Volume 66, Number 1 Mary Clarke, Ph.D. 1/95 File: DIET: MODIFIED/SPECIAL/General |