The most commonly consumed vitamin and mineral supplements provide no consistent health benefit or harm, suggests a new study led by researchers at St. Michael's Hospital and the University of Toronto.
Published in the Journal of the American College of Cardiology, the systematic review of existing data and single randomized control trials published in English from January 2012 to October 2017 found that multivitamins, vitamin D, calcium, and vitamin C—the most common supplements—showed no advantage or added risk in the prevention of cardiovascular disease, heart attack, stroke, or premature death. Generally, vitamin and mineral supplements are taken to add to nutrients that are found in food.
"We were surprised to find so few positive effects of the most common supplements that people consume," said Dr. David Jenkins, the study's lead author. "Our review found that if you want to use multivitamins, vitamin D, calcium, or vitamin C, it does no harm—but there is no apparent advantage either."
The study found folic acid alone and B-vitamins with folic acid may reduce cardiovascular disease and stroke. Meanwhile, niacin and antioxidants showed a very small effect that might signify an increased risk of death from any cause.
"These findings suggest that people should be conscious of the supplements they're taking and ensure they're applicable to the specific vitamin or mineral deficiencies they have been advised of by their healthcare provider," Dr. Jenkins said.
His team reviewed supplement data that included A, B1, B2, B3 (niacin), B6, B9 (folic acid), C, D, and E; and β-carotene; calcium; iron; zinc; magnesium; and selenium. The term "multivitamin" in this review was used to describe supplements that include most vitamins and minerals, rather than a select few.
"In the absence of significant positive data—apart from folic acid's potential reduction in the risk of stroke and heart disease—it's most beneficial to rely on a healthy diet to get your fill of vitamins and minerals," Dr. Jenkins said. "So far, no research on supplements has shown us anything better than healthy servings of less processed plant foods including vegetables, fruits and nuts."