Is it Better to Take Vitamin D Supplements or Soak Up the Sun’s Rays?

We’ve all read the news: Studies suggest that a lack of this “sunshine vitamin” may contribute to higher risks for a host of diseases. Colorectal, breast and prostate cancers, autoimmune diseases such as multiple sclerosis, and even high blood pressure and cardiovascular diseases are associated with vitamin D deficiencies, says Reinhold Vieth, a leading expert on vitamin D and a professor of nutritional sciences at the University of Toronto.

In addition, a groundbreaking Norwegian study published in Cancer Causes and Controls linked higher levels of vitamin D to lower death rates from breast, colon and prostate cancer. And a 2007 study in the Archives of Internal Medicine found that high levels of vitamin D are associated with an overall decrease in total mortality rate.

What’s the best source of vitamin D?

The sun is our most powerful source of vitamin D, which is produced in the skin in response to UVB rays. About 20 minutes of unprotected exposure in the summer, with a UV Index of 7 or higher, will produce 10,000 international units (IU) in a fair-skinned person, says Vieth. But studies have not yet determined what amount of sunlight is needed to produce an adequate amount of vitamin D for disease prevention. And this amount will likely vary for each individual, points out Heather Chappell, senior manager, cancer control policy at the Canadian Cancer Society. “Darker skin is less able to produce vitamin D than fairer skin,” she says. “Age slows down production, too.”

But wait—isn’t “unprotected exposure” to the sun exactly what dermatologists tell us what not to do?

These research results don’t mean we should all start worshipping the sun, given the risks that come with sunburn and the question marks around the science.

“There’s absolutely no evidence the vitamin D you get from sunshine differs from the vitamin D you get from a supplement,” explains Vieth. The Canadian Dermatology Association recommends adults take 1,000 IU daily as a supplement and forgo sun protection for only a couple of minutes a day.

If I opt for a supplement then, how much should I take?

As of November 2010, Health Canada recommends 600 IU per day for adults under age 70 and 800 IU for those over 70.

This story was originally published in Best Health Magazine, Summer 2008.

Next, learn the common myths and truths about vitamin D.