The most commonly consumed vitamin and mineral supplements provide no consistent health benefit or harm, a study has found.
Researchers from the St Michael's Hospital and the University of Toronto in Canada conducted a systematic review of existing data and single randomised control trials published in English from January 2012 to October 2017.
They 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 David Jenkins, lead author of the study published in the Journal of the American College of Cardiology.
"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," said Jenkins.
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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," Jenkins said.
His team reviewed supplement data that included vitamins A, B1, B2, B3, B6, B9 (folic acid), C, D and E; beta-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," 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," he said.