While previous research has suggested a link between low levels of vitamin D in the blood and an increased risk of cardiovascular disease, a new Michigan State University study has found that taking vitamin D supplements did not reduce that risk.

The large-scale study, published in the Journal of the American Medical Association Cardiology, found that vitamin D supplements did not decrease the incidence of heart attacks, strokes or other major adverse cardiovascular events.

"We thought it would show some benefit," said Mahmoud Barbarawi, a clinical instructor in the MSU College of Human Medicine and chief resident physician at Hurley Medical Center in Flint, Michigan. "It didn't show even a small benefit. This was surprising."

His finding was consistent for both men and women and for patients of different ages.

Many earlier studies have found an association of low levels of vitamin D in the blood and an increased risk of cardiovascular disease, suggesting that vitamin D supplements might reduce that risk.

Barbarawi led a team of researchers and reviewed data from 21 clinical trials, including more than 83,000 patients. Half the patients were administered vitamin D supplements, and half were given placebos. The meta-analysis of data showed no difference in the incidence of cardiovascular events or all causes of death between the two groups.

Vitamin D sometimes is known as the sunshine vitamin, because human skin makes vitamin D when exposed to the sun. Thus, those living farthest from the equator tend to have lower levels of vitamin D in their blood.

While some studies have found a link between low levels of the vitamin and an increased risk of adverse cardiovascular events, Barbarawi's study suggests that other factors, such as outdoor physical activity and nutritional status, might explain the association.

Barbarawi also noted that even though his findings showed no effect on heart health, some patients, such as those being treated for osteoporosis, still might benefit from the supplements.

As a result, he suggests that doctors and patients think twice about taking the vitamin to minimize the chances of a heart attack or other cardiovascular issues.

"We don't recommend taking vitamin D to reduce this risk," Barbarawi said.