Men with low levels of vitamin D have an elevated risk for a heart attack, researchers said on Monday in the latest study to identify important possible health benefits from the "sunshine vitamin."
In the study, men classified as deficient in vitamin D were about 2 1/2 times more likely to have a heart attack than those with higher levels of the vitamin.
"Those with low vitamin D, on top of just being at higher risk for heart attack in general, were at particularly high risk to have a fatal heart attack," study author Dr. Edward Giovannucci of the Harvard School of Public Health and Brigham and Women's Hospital in Boston said in a telephone interview.
The study involved 454 health professionals ages 40 to 75 who had suffered a nonfatal heart attack or died of heart disease, as well as 900 other men with no history of cardiovascular disease. They were followed for 10 years after providing blood samples to measure their vitamin D levels.
The researchers compared those who were deficient in vitamin D -- no more than 15 nanograms per milliliter of blood -- to men who were in at least the lower end of the normal range -- at least 30 nanograms per milliliter of blood.
The body makes vitamin D when the skin is exposed to sunlight. Milk commonly is fortified with it, and it is found in fatty fish like salmon.
Vitamin D helps the body absorb calcium and is considered important for bone health. In adults, vitamin D deficiency can lead to osteoporosis, and it can lead to rickets in children.
A number of recent studies have indicated vitamin D also may offer a variety of other health benefits, including protecting against types of cancer including colon and breast cancer, peripheral artery disease and tuberculosis.
In January, researchers led by Dr. Thomas Wang of Harvard Medical School reported findings that fit with the new study, showing that people with low vitamin D levels have a higher risk for heart attack, heart failure and stroke.
Giovannucci said there is enough evidence about the value of vitamin D to encourage people to ensure they have normal levels. He said people can learn their vitamin D levels by having their doctor give them a blood test. Those whose levels are too low can take vitamin D supplements, he said.
"Many people have low vitamin levels," Giovannucci said.
"Traditionally, physicians have only been concerned about the bone effects. But perhaps having these chronically low levels of vitamin D may be having these subtle physiological changes in a lot of tissues," Giovannucci added.
Giovannucci said there could be a number of ways in which vitamin D may protect against heart attack. He said it might lower blood pressure, regulate inflammation, reduce calcification of coronary arteries, affect the heart muscle or reduce respiratory infections in winter.