Millions of people who take multivitamins everyday may not be reaping the perceived health benefits, according to new research published in the Journal of the American Medical Association.
One in three American adults take daily multivitamins to prevent disease, but the research suggests they don't help you live longer.
The study looked at nearly 400,000 generally healthy adults over a 20-year period and found no evidence that prolonged daily multivitamin intake reduced the risk of death. Instead, the results found a four per cent higher mortality risk in users in the study's early years.
"What they found was going to be a disappointment to anybody who thought taking a multiple vitamin might extend your life. It does not lead to longevity, and this adds to other research that has shown more or less the same thing," said Dr. Neal Barnard, author of the study's commentary.
There are benefits from taking multivitamins for some people, Barnard said, including pregnant women and people with the ocular disease macular degeneration. There's also some evidence to suggest they can reduce the risk of dementia late in life.
"That's the good news. But there's also some pretty bad news as well," Barnard said. "Multiple vitamins throw a whole bunch of vitamins together. There can be some that can actually be harmful to you if you're taking them in excess."
The biggest risk tends to be the iron added to the vitamins, which can be harmful if a person is already getting enough iron in their diet. Iron overload can lead to heart problems, Barnard said.
Nutrients Copper and beta-carotene can also be harmful if taken in excess. Copper overload has links to Alzheimer's disease and beta-carotene in vitamin form could increase the risk of cancer, according to Barnard.
He said these "toxic effects" could be the reason for an increase in mortality in the early years of the study.
"It's better to get your vitamins from food because when you get them in food, you get the full array of vitamins that nature brings to you," Barnard said.
"What you really want to look for is vegetables and fruits, and have a lot of them."
There are some vitamins that need to be supplemented for some people, Barnard said, such as B-12 and vitamin D. It is best to get those as individual supplements rather than in a multivitamin.
