Vitamin D: Wonder Drug or Wonder Hype?

Doctors and health nuts have been gulping down vitamin D supplements lately, but there’s precious little science suggesting that they do anything. Conventional wisdom holds that vitamin D, which most people get through milk and exposure to sunlight, strengthens your bones and immune systems, while lowering the risk for serious diseases. But there’s not much clinical data to support those claims, the New York Times reports.

Much of the hype around vitamin D comes from observational research, but people with high levels of vitamin D tend to be healthier people in general. “Correlation does not necessarily mean a cause-and-effect relationship,” said one professor. So a new large study is under way to test the effects of the vitamin on 20,000 older adults. The trial could help set a new, higher daily vitamin D recommendation—something most experts believe is overdue. (More vitamin D stories.)