Don't throw away your vitamin D tablets based on the latest news on the supplement's failure to prevent breast cancer in postmenopausal women. The Women's Health Initiative study published this week shows that after seven years of calcium and vitamin D supplementation, there was no reduction in breast cancer risk. In retrospect, this is what one would have expected: The vitamin D dose of 400 IU seemed more than enough when the study began in the early 1990s, but science has moved on. In fact, that level is barely sufficient for what is a major deficiency common to most Americans and Europeans. In addition, many of the participants in the placebo group, or control arm of the study, diligently continued taking their calcium and vitamin D supplements, limiting the effectiveness of a randomized trial. So what does this mean to women—and men for that matter?
Michael Holick, a vitamin D expert in the Department of Endocrinology, Nutrition, and Diabetes at Boston University Medical Center, just last year in the New England Journal of Medicine reviewed the abundant and highly convincing laboratory and clinical research that supports the pivotal role of adequate vitamin D levels both in bone health and in cutting the risk of chronic disease, including many cancers. Here's a summary of five key points to keep in mind:
1. Most Americans are vitamin D and calcium deficient. This is particularly so for the elderly, the obese, and those who have little or no sun exposure. (Estimates of insufficiency in vitamin D levels among those in the United States and Europe range from 40 percent to 100 percent.)
2. Several randomized trials have unequivocally shown the benefits of vitamin D supplementation, including an increase in bone density and a decrease in fractures.
3. Compelling evidence suggests taking vitamin D supplements results in a reduction of common cancers—including breast, prostate, and colon tumors—particularly when in people with low initial levels of vitamin D. But no definitive randomized trial has tested this at intake levels in the range of 1,000 IU.
4. Among experts in the field, there's a general consensus that current government guidelines for vitamin D intake in the range of 400 to 600 IU are inadequate for most people. The number should be twice that, many say.
5. With the exception of a small increase in kidney stones, there is no evidence of harm in taking vitamin D and calcium supplements.
To avoid vitamin D deficiency, Holick recommends that most adults take 800 to 1,000 IU of vitamin D3 daily or 50,000 IU of vitamin D2 every two to four weeks. (Vitamin D2 is metabolized more gradually than the D3 form of the nutrient, though both fulfill the body's need for vitamin D.) Under certain circumstances—like pregnancy, obesity, or particular forms of kidney or gastrointestinal disease—the ideal dose might double.