Calcium intake is important for many reasons, including the important role of forming the structures that strengthen and shape teeth and bones. As people age, bones become less dense, more brittle, more likely to break, and may result in osteoporosis. For years, high calcium intake has been advocated for preventing osteoporosis and related fractures. However, large prospective studies that followed people for many years have cast doubt on the benefits of high calcium intake, and subsequent randomized trials of calcium were conducted to test what effect it might have on fracture rates.
In 2005, two British studies showed that calcium did not prevent fractures—even when taken in combination with vitamin D. In 2006, a large American trial (the Women’s Health Initiative) showed that postmenopausal women who took a calcium-vitamin D combination were no less likely to break their hip than women who took a placebo pill, although the density of their hip bones increased slightly. In 2007, a Swiss and American team, including researchers from Harvard, reported the results of a meta-analysis of more than a dozen studies of calcium that found no connection between high calcium intake, from either food or pills, and lower hip fracture risk. In fact, when they limited their analysis to 4 randomized clinical trials with separate results for hip fractures, they found that extra calcium increased the risk.
Although a certain level of calcium intake is undoubtedly important for strong bones, amounts above that level might not be beneficial. Indeed, many Americans receive adequate calcium via dairy products and supplements. One theory is that calcium taken in large amounts may interfere with absorption of phosphorus, which is also crucial to maintaining bone strength. Further, added calcium isn’t all that beneficial if vitamin D intake is low. The body needs vitamin D to absorb calcium.
According to current recommendations, Americans over age 50 are supposed to get 1,200 mg of calcium daily. Dr. Walter C. Willett, chair of the Harvard School of Public Health’s nutrition department, believes that many Americans are getting more calcium than they need. In his opinion, 600 mg is probably enough for most people to keep their fracture risk low, but because extra calcium might be protective against colon cancer, he sees a daily intake of 600 to 1,000 mg as a reasonable goal. There may be real drawbacks to overdoing calcium, especially if dairy foods are the source. Dr. Willett points to studies linking high consumption of dairy products to ovarian and prostate cancer, noting that the relationship seems particularly strong for metastatic and fatal prostate cancer.
Current guidelines say Americans age 50 and older should get 400 to 600 international units (IU) of vitamin D. But a growing number of experts, including Dr. Willett, say that’s not enough, and that 800 or even 1,000 IU of vitamin D would not only benefit bones but possibly prevent some cancers and other problems.
(Source: HEALTH-beat, Harvard Health Publications, May 27, 2008)
