"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 incidences 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.
Mahmoud Barbarawi, Babikir Kheiri, Yazan Zayed, Owais Barbarawi, Harsukh Dhillon, Bakr Swaid, Anitha Yelangi, Saira Sundus, Ghassan Bachuwa, Mohammad Luay Alkotob, JoAnn E Manson.
Vitamin D Supplementation and Cardiovascular Disease Risks in More Than 83 000 Individuals in 21 Randomized Clinical Trials: A Meta-analysis.
JAMA Cardiol. Published online June 19, 2019. doi: 10.1001/jamacardio.2019.1870.