Medical researchers are homing in on a wonder drug that may 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.
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.
Current guidelines call for blood levels of about 30 nanograms per milliliter. By that definition, perhaps 10% to 15% of white people in the U.S. and 50% of the black population is deficient in summer, with the percentages rising in winter when there is less sunlight.
Many researchers say that people should be striving for average blood levels of 50 to 60 nanograms per milliliter, at which level the bulk of the U.S. population would be considered deficient.
Most researchers in the field now take supplements of at least 1,500 IUs per day. Most recommend taking no more than 4,000 IUs because of potential toxicity.
Experts attribute the vitamin D deficiency, in part, to modern lifestyles, which have taken people off the farm and into offices and factories. Video games and computers have brought children indoors from the playing field, minimizing their exposure to sunlight. Fear of cancer and increasing use of sunblock may also have contributed.
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 much larger ongoing study. The men all submitted blood samples when they enrolled in the study, mostly in 1993 to 1995, and the samples were stored.
In 10 years of follow-up, the team identified 454 men who had a heart attack. They carefully matched these men with about 900 other study members who did not have an attack, then measured vitamin D levels at study entry.
They reported in the current issue of the Archives of Internal Medicine that men with blood levels below 15 nanograms per milliliter had 2 1/2 times the risk of having an attack or dying.
When they controlled for all other possible factors, such as hypertension, obesity and high lipid levels, the risk was still twice as high as it was for the controls.
Men with levels between 15 and 29 nanograms per milliliter also had an increased risk. Unfortunately, Giovannucci said, there were not enough men in the group with levels above 35 nanograms per milliliter to determine whether higher levels are more protective.