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.
The findings are "not out of left field," he said. Many epidemiological studies have found a higher rate of heart attacks at higher latitudes, lower altitudes and in winter -- all of which correlate to decreased exposure to sunshine.
