Spend a few minutes soaking up some rays and your body will start to pump out more vitamin D. Many health officials believe Americans are D-deficient, but in the age of sunblock and self-tanners, how many vitamin-D pills should we be popping? New guidelines for the optimal dietary dose are expected in the fall, and definitive studies on vitamin D’s effects on cancer, heart disease and cognition are ongoing. In the meantime, here’s where the science stands. CancerVitamin D may prevent cancer by suppressing the cell growth and blood-vessel formation that feed tumors. At least that’s the idea, based on animal studies and analyses of human cells. But trials in which patients take vitamin D have not shown a consistent lowering of cancer risk. One four-year trial of 1,200 postmenopausal women found a 77% lower risk of all cancers among those taking calcium and 1,000 IU of vitamin D a day than among those taking a placebo. A larger study, however, in which subjects took 400 IU of vitamin D — in the absence of an official daily recommended intake, that’s the “adequate” intake for adults ages 51 to 70 — did not show lower breast-cancer risk. The data are strongest for colorectal cancer: subjects with higher blood levels of vitamin D were half as likely as those with lower levels to develop the disease.
