Calcium, Vitamin D, and Cancer
Cancer is the second major cause of death in the United States. While techniques of cancer diagnosis and treatment have steadily improved, they remain inadequate; and for this reason, scientists continue to investigate possible methods of
Numerous supplements and herbal extracts have shown promise for helping to reduce cancer risk. However, the evidence isn’t yet strong for any of these potential “chemopreventive” agents. The major obstacle is a generic one: No matter what the treatment, whether natural or man-made treatment, it is difficult to determine whether a proposed cancer-preventing treatment actually works.
In fact, some of the largest and most expensive double-blind studies in history were those performed to test the efficacy of
Nonetheless, natural products continue to be investigated as possible “chemopreventive” agents. Much of the evidence that makes it into the media involves studies conducted in a test tube. “Observational studies” constitute another type of widely reported evidence. In such studies, huge numbers of people are observed for a long period of time, and researchers try to find correlations between (for example) what people eat and what diseases they develop. Unfortunately, both test tube and observational studies are highly unreliable—it was studies of these types that led to the giant, ultimately negative studies of vitamin E and beta-carotene. Only double-blind studies can really prove a treatment effective, and these remain relatively few in the field of cancer prevention.
Calcium is one of the supplements still under study as a cancer-preventive treatment. Numerous observational and some double-blind studies have found evidence that calcium supplementation may reduce the risk of colon cancer. However, not all double-blind studies have been positive, and the issue remains in doubt.
New findings do support the possibility that calcium supplements have an anti-cancer effect, at least in women. This evidence comes from a study primarily designed to test the effectiveness of calcium and vitamin D for preventing osteoporosis in postmenopausal women. The researchers who conducted this trial additionally examined cancer incidence. The results were encouraging. In this four-year study of 1179 women, use of calcium, especially when combined with vitamin D, significantly reduced overall cancer risk.
Note, however, this study involved only women. There are some concerns that calcium supplements might increase risk of prostate cancer (in men).
Lappe JM, Travers-Gustafson D, Davies KM, et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr . 2007;85:1586-91.
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