Calcium serves many functions in the body, but the main one is to form the structures that give our bones and teeth their strength and shape. As we get older, our bones start to thin out bit by bit, so they become less dense, more brittle, and more likely to break. When this thinning advances to a certain point, it’s called osteoporosis.
Each year in the United States there are 1.5 million bone fractures associated with osteoporosis, and 250,000 of those breaks will involve a hip.
Research questions the calcium-strong bones link
For years, high calcium intake has been portrayed as one of the best things you could do to prevent osteoporosis and related fractures. But when researchers started to crunch the data from large, prospective studies that followed people for many years, the benefits weren’t so clear-cut. These findings led to randomized trials of calcium to test what effect it might have on fracture rates.
The tide started to turn in 2005 when results from two British studies showed that calcium didn’t prevent fractures — even when taken in combination with vitamin D. The next year, results from 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 some researchers from Harvard, reported the results of a meta-analysis of over a dozen studies of calcium. They 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 four randomized clinical trials with separate results for hip fractures, they found that extra calcium increased the risk.
The whys and wherefores
While a certain level of calcium intake is undoubtedly important to keeping bones strong, amounts above that level might not do much good. One reason extra calcium didn’t show any benefit in the Women’s Health Initiative may have been because the women in that study were, on average, already getting over 1,000 milligrams (mg) daily. And they weren’t all that unusual. Many Americans already get plenty of calcium by eating dairy products and taking supplements.
Another theory: calcium in large amounts may interfere with absorption of phosphorus, which is also crucial to maintaining bone strength. Phosphorus deficiency isn’t a major problem in well-fed populations, but it’s possible that extra calcium pushes some people into it, especially if their diets don’t include much protein.
Another factor may be that added calcium isn’t all that beneficial if vitamin D intake is low. The body needs vitamin D to absorb calcium, and depending on how you define it, between 30% and 60% of us have less-than-optimal levels of vitamin D in our blood.
What should you do?
According to current recommendations, Americans over 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 in the 50-plus age bracket are supposed to 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 IU, or even 1,000, would not only benefit our bones but possibly prevent some cancers and other problems.
Vitamin InformationUnderstanding how vitamins and minerals interact in our body gives us a valuable means of taking our health into our own hands. Research into the effects of these micronutrients has been enlightening. For example, we now know that a large fraction of Americans are not getting enough vitamin D, and the range of consequences may be far greater than we thought. Recent studies suggest that vitamin D does more than help build strong bones; it may help to prevent hypertension, certain types of cancer, and some autoimmune diseases. We also believe, with an increasing degree of certainty, that getting enough folic acid can counteract some of the adverse effects of consuming alcohol.
Researchers are constantly making such discoveries, and often their findings have far-reaching effects. But it’s worth keeping in mind that while nutrition research can yield powerful answers, it also raises new questions. Nutrition is endlessly complex, and the research is invariably in a state of flux. Not only do nutrients interact with one another (making it difficult to isolate their effects) but they also interact with genes, drugs, and even lifestyle factors. For some nutrients, such as selenium, there’s a narrow range between too little and too much, and that amount varies from person to person.
This Special Health Report provides the latest evidence and mineral and vitamin information so that you can make healthy choices about what foods to eat and what supplements to take. Because nutritional science continues to evolve, this report also contains tips on how to judge new studies on vitamin benefits and put the findings in context.
Prepared by the editors at Harvard Health Publications in consultation with Meir J. Stampfer, M.D., Dr.P.H., Professor of Epidemiology and Nutrition, Harvard School of Public Health. 45 pages. (updated: 2008). $18.00
http://www.health.harvard.edu/special_health_reports/
© 2000–2008 Harvard University.
