Word: vitaminous
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...disappointment," says study author Dr. Rowan Chlebowski at Los Angeles Biomedical Research Institute and Harbor-UCLA Medical Center. "Basically we have an agent in vitamin D that is almost free and with little toxicity, and wouldn't it be great if it did substantially reduce the risk of breast cancer...
...women participating in the WHI - a multiyear government trial investigating a range of women's health issues, from hormone therapy to heart disease, cancer and fracture risk - half were given 1,000 mg of calcium and 400s IU of vitamin D daily, while the other half were not. After seven years, 528 women in the supplement group and 546 women in the control group had developed invasive breast cancer, an equivalent rate, indicating no effect from the vitamin D. Earlier observational trials had found positive links between women's taking higher amounts of supplemental vitamin D and lower breast-cancer...
...thing, the dose of vitamin D supplementation used in the trial, 400 IUs, was relatively low. In the years since the study began in 1993, nutritionists have learned much more about the critical role that vitamin D plays in a wide range of cellular functions, and many now recommend up to 2,000 IUs daily for adults. Most people get very little vitamin D from their diet - the richest sources of the vitamin are dairy products and green leafy vegetables - so supplementation is the only way to reach recommended levels. "Four hundred IUs is just not a lot," says...
Confounding the results even more is the fact that calcium and vitamin D supplementation is now routine therapy for postmenopausal women to protect against bone fractures. So about 15% of the women in the placebo group were allowed to continue taking their vitamin D supplements for bone health (some were taking up to 600 IUs per day), which could explain why there was little difference between the two groups in breast-cancer rates. "This is a potential problem that confounds the results of this particular trial," says Dr. Powel Brown, a professor of medicine at Baylor College of Medicine...
Those studies might expose other factors affecting vitamin D levels that the WHI trial was not designed to track. Exposure to sunlight, for example, boosts vitamin D production in the body, and in the WHI trial, the women with the highest levels of 25-hydroxyvitamin D tended to be the leanest and most physically active, suggesting that they might spend more time outdoors...