More than half of American adults take a vitamin or mineral supplement, says Harvard Medical School's Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital. And many wonder whether they really should be. Or whether they're taking the right ones, or the right doses.
"It's really important to get help separating fact from fiction," Manson says, "because there's so much hype about dietary supplements, and very often the benefit is quite limited."
Quite limited indeed, at least for the general population, according to the evidence so far. Manson is lead author on a sweeping new overview of vitamin and mineral supplements in the journal JAMA, and here's how she sums it up:
The key message is that for most of the population, it's best to get these vitamins and minerals from the diet, from foods. That's where they're best absorbed, and they're in the optimal biological ratios.
However, some subgroups of the population may benefit, either because of a life stage that they're in — such as pregnancy, infancy, or older age groups — or because they have a medical condition that could interfere with absorption or metabolism of a vitamin or mineral, or are taking medications that may have that adverse effect.
So, big point one, healthy food is better than pills.
Point two: For certain subgroups, there's enough evidence to support taking vitamins and minerals — but for the generally healthy population with good diets, there is not.
Some excerpts from my conversation with Manson:
How would you sum up where you got the information on which you based this overview?
From several professional society guidelines, and from randomized clinical trials. We've done multiple reviews of the literature and we've done many of the trials ourselves, testing the role of higher doses of some of these vitamins and minerals — vitamin C, vitamin E, beta-carotene, folic acid. We're testing vitamin D and Omega-3s now, as well as multi-vitamins.
I think many people would be surprised by the clear message that if you're generally healthy and well-nourished and relatively young, you do not need vitamins or minerals.
The key point is that it's best to get these vitamins and minerals from foods, from the diet, and in a healthy general population, there is no additional benefit from supplementation. And there are advantages of getting the vitamins and minerals from foods because they're better absorbed that way.
So we tried to develop a framework for thinking about which subgroups may benefit, either because they're at a life stage when supplementation provides benefits or because they're in a high-risk subgroup where there is a benefit of taking supplements.
The overview lays them out simply. For example:
- Pregnancy: folic acid, prenatal vitamins
- Infants and children: for breastfed infants, vitamin D until weaning, and iron from age 4-6 months
- Midlife and older adults: Some may benefit from supplemental vitamin B12, vitamin D and/or calcium
- Other high-risk subgroups: Medical conditions that interfere with nutrient absorption or metabolism, osteoporosis, selected medication use, and others.
But I think many will wonder at this point why many doctors routinely recommend multivitamins even to healthy younger folks.
In terms of multivitamins, there is one large-scale randomized trial that suggests there may be a modest reduction in the risk of cancer, and we are trying to see if those findings can be replicated. We're actually doing a large randomized trial of multivitamins right now, a second trial, looking at the effects in reducing risk of cancer and cardiovascular disease.
Overall, there isn't yet clear evidence that people who have a healthy, well-balanced diet will get benefits from multivitamins or other dietary supplements.
However, if someone is concerned about their diet and they don't think that it's well-balanced, we should encourage them first to try to have the more balanced diet, but it is a reasonable form of insurance to take a multivitamin.
In the article, you also mention quality control.
It's important to know that you're taking a high-quality supplement in terms of getting the amount of vitamin or mineral that it says it has on the label and also that there isn't contamination by microbes, heavy metals or toxins.
One way to ensure that you're getting a product that has undergone independent quality control testing and independent audit is to look for labels such as U.S. Pharmacopeia, NSF International or UL, or other information on the label suggesting it's undergone an independent quality control test.
It's amazing to me that typical chain pharmacies offer row after row of these supplements, given how little strong evidence there is for most of them.
That's why we thought it was so important to write an article like this, because it's really important to separate the hype from the evidence, and separate fact from fiction.
Generally, patients are overwhelmed by all of the promotions of vitamins and minerals and other dietary supplements — they're really bombarded by advertising for them and seeing them in every supermarket and drugstore.
And clinicians receive little formal training on how to advise patients about the use of vitamins and minerals. So we tried to summarize the evidence and provide a framework for thinking about who doesn't need these supplements and who may benefit.
And what you're most concerned about is high doses of single vitamins or minerals?
Some of the individual supplements are more than 10 times the recommended intake. The single supplements that people most often take in high doses that we should be most concerned about are vitamin E and beta carotene, which have been linked to some risks when taken in very high doses. That's what we're trying to discourage: very high-dose supplementation of individual vitamins or minerals or other dietary supplements.
And looking forward?
We will be reporting later this year the results of our large-scale trial of vitamin D and omega-3s, which is looking at whether moderate-to-high-dose vitamin D or omega 3s can lower the risk of cancer and cardiovascular disease. We're also testing multivitamins and prevention of cancer and cardiovascular disease — those results should be available within about two to three years.