Vitamin D, Calcium vs. Breast Cancer

What About the Sun continued...

Excessive vitamin D can lead to toxicity. You should talk to your doctor about the use of supplements prior to taking them.

Dairy products and oily fish like salmon and tuna are some of the best food sources for vitamin D, but it would be difficult to get that much vitamin D in foods alone.

The easiest way for the body to get vitamin D is through sun exposure, because ultraviolet rays from the sun trigger the natural synthesis of vitamin D.

An 8-ounce glass of milk contains only 100 IU of vitamin D. By comparison, someone who spends 10 to 15 minutes in the sun on a sunny day without sunscreen can absorb 2,000 to 5,000 IU of vitamin D if 40% of their body is exposed, Garland says.

Recommending sun exposure is controversial because of the risk of skin cancer, and Garland tells WebMD that it is possible to get all the vitamin D the body needs through foods and dietary supplements.

"Ideally a mix is good, with some vitamin D coming from food, some from supplements, and some from sun if people can handle sunlight," he says.

Considering the Evidence

The American Cancer Society, the National Council on Skin Cancer Prevention, and other interested health groups from the U.S. and Canada met early last year to consider the evidence on sun exposure, vitamin D, and health.

The coalition concluded that the evidence is "strong" linking vitamin D to a decreased risk of bone fractures in the elderly. With regard to cancer risk, the group concluded that "a growing body of evidence" suggests a protective benefit for some cancers.

The coalition noted that the risks of unprotected exposure to the sun as a source of vitamin D had to be weighed against the benefits.

"To minimize the health risks associated with ultraviolet B (UVB) radiation exposure while maximizing the potential benefits of optimum vitamin D status, supplementation and small amounts of sun exposure are the preferred methods of obtaining vitamin D," the group concluded.

McCullough says 10 minutes a day of unprotected sun exposure in the spring and summer is plenty for most people, and more than this is too much.

"We need to make sure that people don't interpret this as meaning that going to the beach and sunbathing for hours without sunscreen is a good idea," she says.