Medical researchers are homing in on a new wonder drug that can significantly reduce the risk of heart disease, cancer, diabetes and many other diseases – sunshine.

A study released today found that men who are deficient in the so-called sunshine vitamin, vitamin D, have more than double the normal risk of suffering a heart attack.

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

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

“We don’t have a cause-and-effect relationship here yet,” said biochemist Hector DeLuca of the University of Wisconsin, to prove that higher doses of vitamin D prevent these diseases. DeLuca 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 recently, vitamin D was viewed primarily as a protective agent against diseases of the bone, such as rickets, osteomalacia and osteoporosis. Recommendations for the vitamin are based on preventing these disorders and call for a small intake – a minimum of 400 international units (IUs) per day and perhaps twice that for elderly people.

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.

In the new analysis, Dr. Edward Giovannucci of the Harvard School of Public Health and his colleagues studied 18,225 men enrolled in the Health Professionals Follow-up study, a subgroup of a larger ongoing study.