Osteoporosis
FOR years, both the medical profession and the public have focused almost exclusively on calcium as the nutrient for building bones. After all, the argument goes, bones contain a lot of calcium; so if we just take more calcium, our bones will be stronger. However, calcium is just one of the many nutrients involved in the prevention and treatment of osteoporosis. Taking calcium supplements alone, particularly in large amounts, may not do much good and, in some cases, may even cause harm. The reality is that bone tissue is complex, dynamic and alive, and like other tissues in the body, has a wide range of nutritional needs.
Although calcium deficiency is unquestionably one cause of osteoporosis and while calcium supplements can have preventive or therapeutic value in certain circumstances, we cannot just drink more milk or take more calcium supplements and expect our bones to turn out perfectly fine. Having said that, taking an adequate quantity of absorbable calcium is one of the goals of an osteoporosis prevention programme.
Studies on the relationship between calcium intake and osteoporosis are many and varied, and have produced conflicting and confusing results. Opinions about calcium have changed several times over the years, from effective, to ineffective, to partially effective.
The problem with too much calcium
Today there are concerns about the possible adverse consequences of taking too much calcium. One argument is too much calcium may interfere with the absorption or utilisation of other essential nutrients. Studies have shown calcium interferes with the absorption of iron. This inhibition is more pronounced with increasing calcium doses, but can occur at intakes of calcium commonly found in the diet. Oral administration of excess calcium also decreased the absorption and tissue levels of zinc in rats. Although short term studies (up to 45 days) in healthy male rats failed to find that 2,000 mg/day of calcium affected zinc balance, it is possible that taking high doses of calcium for years could deplete zinc reserves.
However, the most significant concern about taking too much calcium is that it could lead to magnesium deficiency. Magnesium deficiency is one of the most widespread and clinically significant nutritional problems in the United States. The adverse effect of calcium supplementation on magnesium levels has been shown in animal studies. Rats that were fed a diet containing 1.5 percent calcium had lower levels of magnesium in various tissues of their body than rats fed only one-third that much calcium.
Why are such high doses recommended?
Doctors who recommend 1,500 mg/day of calcium do so because of a study that showed that such a large dose is necessary for elderly women to maintain calcium balance. However, few doctors who prescribe 1,500 mg/day of supplemental calcium have stopped to consider what maintaining calcium balance actually means. In nutritional studies, the term balance refers to the difference between the amount of a nutrient entering the body and the amount leaving. if someone is in positive calcium balance, they are excreting less than they are taking in, and their total body calcium content is increasing. If they are in negative calcium balance, they are excreting more than they are taking in, and their total-body calcium content is declining. For a person in calcium balance (also called zero calcium balance), the intake and output are the same and the total-body calcium content remains steady. Doctors assume that maintaining calcium balance is the same as preventing bone loss.
Taking excessive amounts of calcium without adequate magnesium can accelerate both osteoporosis and soft-tissue calcification. This unhealthy situation can be misinterpreted as desirable, if calcium balance is the sole criterion on which results are based. Human autopsy studies have shown a close correlation between osteoporosis and calcification of the abdominal aorta. Since magnesium deficiency can promote both osteoporosis and aortic calcification, it is possible that magnesium is the primary factor and that calcium is secondary.
