Sunshine may be nature's disease fighter

Just last week, another study found that low levels of vitamin D increased the risk of diabetes, and a study last month linked deficiencies to an increased risk of dying from breast cancer.

The findings join a growing body of evidence indicating that an adequate level of the vitamin, which many people can get from 20 minutes in the sun, is crucial to maintaining good health.

Not every scientist agrees that vitamin D is so crucial to well-being, and there is controversy about what should be considered an adequate level of the compound in the blood. But sentiment is gradually shifting toward a higher intake.

"We don't have a cause and effect relationship here yet" proving that higher doses of vitamin D prevent such diseases, said biochemist Hector DeLuca of the University of Wisconsin, who was the first to demonstrate how the vitamin interacts with the endocrine system, which manages the body's hormonal balance.

But the links are so suggestive "that we have to pay attention to keeping blood levels up where they will protect," he said. Until the protective effect is proved, he added, "what's wrong with keeping an adequate level of vitamin D in the blood in case it is?"

Until recently, vitamin D was viewed primarily as a protective agent against diseases of the bone, such as osteomalacia (known as rickets in children) and osteoporosis. Current recommendations for the vitamin are based on preventing these disorders and call for a relatively small intake -- a minimum of 400 international units, or IUs, per day, and perhaps twice that for the elderly, who may not get outdoors as often.

The vitamin is produced from natural precursors in the body by exposing skin to ultraviolet B in sunlight. Caucasian sunbathers can get 20,000 IUs in 20 minutes at noon in summer. But any further exposure simply damages skin.

Darker-skinned people need three to five times the exposure to produce the same amount. Sunblock interferes with production by screening out ultraviolet light.

The primary sources of vitamin D in the diet are milk, which is fortified to yield about 100 IUs per glass, and oily fishes, which have a high content.

To have an adequate intake, most people must take supplements or spend more time in the sun -- a recommendation that dermatologists generally oppose because of the risk of skin cancer.