The Family Health Guide
The vitamin D-cision brings surprises
After a decade of glowing reports for vitamin D, a panel of experts has seemingly thrown the dimmer switch on the sunshine vitamin. The glowing reports largely have come from what are called observational studies. Many such studies have shown that people with higher blood levels of vitamin D have lower rates of heart disease, several autoimmune diseases and several forms of cancer. The problem with observational studies, however, is that such studies cannot prove that the reason for lower rates of these various diseases is the higher blood levels of vitamin D. And they cannot prove that taking a vitamin D supplement daily to raise blood levels of vitamin D will lower the rates of these diseases. Only randomized, controlled trials in which large numbers of people get vitamin D supplements or a placebo ("sugar pill") can prove that taking supplements, and raising blood levels, actually achieves a reduction in the rates of disease. As of this time, there have been relatively few such large-scale randomized trials of vitamin D supplementation.
In revising the 1997 dietary guidelines, a panel convened by the Institute of Medicine (IOM) concluded that there wasn't enough solid evidence to support taking vitamin D to stave off a host of disorders from colon, breast, and prostate cancer to heart disease, arthritis, and autoimmune conditions. The panel's report, released on Nov. 30, 2010, also throws cold water on the assumption that most North Americans are deficient in vitamin D. The new recommended intake of the vitamin is higher, but not nearly to the level some advocates had anticipated and called for.
Many researchers had argued that an update of the vitamin D guidelines was long overdue because of new evidence for the vitamin's expanded health benefits—evidence largely from observational studies. In response, the United States and Canadian governments asked the IOM, an independent body of medical scientists, to review the research and, if needed, change the recommendations for vitamin D and calcium. Calcium was included because the two nutrients are inseparable; vitamin D is essential to the metabolism of calcium.