For decades, doctors have warned the public about the dire risks of too much sunbathing and ultraviolet radiation, and the public has responded by slathering on sunblock. Now, medical advice is swinging back in the other direction. A host of new studies have indicated that vitamin D, which is produced by the body when exposed to the sun's ultraviolet rays, helps reduce the risk of heart disease, cancer, diabetes, and other diseases. The latest study followed over 18,000 men and found that men with vitamin D deficiency were more than twice as likely to have a heart attack than those with normal levels of the nutrient. They were also more likely to die as a result of heart disease. The study was published in the Archives of Internal Medicine [subscription required]. Researchers corrected for such factors as family history, weight, and cholesterol levels, and say the results were striking enough to warrant new recommendations. Lead researcher Edward Giovannucci says it's advisable to go out in the sun, sans sunblock, for a brief period each day. On a sunny day in the summer, just 10 minutes outside in shorts and a T-shirt will generate enough vitamin D to reach the higher levels found protective in the study, Giovannucci said. Light-skinned people, the group with the highest risk of skin cancer, are the most efficient at producing vitamin D and need the least time in the sun, he said. Darker-skinned people need two to three times longer, he said.