Vitamin supplements show little evidence of health benefits and some could actually be harmful, suggests new research.
Researchers from the University of West Virginia found that most dietary supplements do not have health benefits, and some could even cause harm.
The team reviewed data from over 270 trials, involving almost one million people. They looked into the effects of 16 different nutritional supplements, along with eight dietary interventions, on mortality and heart health.
Of the nutritional supplements reviewed, the only two that were found to be beneficial were folic acid and omega 3. While healthy eating patterns, such as the Mediterranean diet, or eating low fat, were found to have no effect on heart health. However, a diet low in salt was found to be beneficial for cardiovascular health.
The team also discovered that combining vitamin D tablets with a calcium pill could actually increase the risk of a stroke. But taking calcium or vitamin D alone seemed to have no effect on mortality or heart health whatsoever.
"The reason we conducted this study was that millions of people in the United States and across the world consume supplements or follow certain dietary patterns, but there was no good-quality evidence to suggest that these interventions have any effect on cardiovascular protection," lead author Dr Safi Khan said.
However, he admitted that there were limitations to these results, as most studies relied on participants keeping track of their supplement intake and eating habits through the use of food diaries. Evidence supporting the dangers of combining calcium and vitamin D supplements was not robust.
NHS guidance states that most people without pre-existing medical conditions do not need to take supplements, as a balanced diet should provide adults with all the necessary nutrients to stay healthy. The only exception is vitamin D which should be taken daily from October to May.
Susan Jebb, professor of diet and population health at University of Oxford, said: "This review confirms the vast majority of previous research that has failed to find benefits of most nutritional supplements. But the suggestion that dietary interventions have no benefit does not reflect the totality of the evidence."