Can multivitamins be harmful?

Dr. Darria Long Gillespie, MD
Emergency Medicine
Just like any substance in the world, multivitamins can be dangerous if not used as directed, or if taken by certain patients.

For one thing, it is possible to overdose on multivitamins. This is especially a risk for products that have iron in them, which can cause poisoning, especially in children.  

For patients who are on various medications, I always want them to mention their multivitamin to their doctors, just to make sure they’re not taking anything that could interact with it. 

In addition, multivitamins can be harmful in another sense -- if you take them to replace a good diet.
Taking multivitamins can be harmful in certain instances. An example would be a child taking adult dose multivitamins. Additionally some vitamins include iron, which can also be harmful in children. Eating too many vitamins can lead to problems associated with the specific vitamin toxicity. Some vitamins are easily excreted in your urine, while others tend to build up in your body. In general, taking the prescribed or labeled dosing can help alleviate harmful side effects from multivitamins.
Celeste Robb-Nicholson
Internal Medicine
Probably not, but research suggests that multivitamins may not be all they're cracked up to be. And they do not compensate for most dietary deficiencies. Moreover, many multivitamins contain some micronutrients in amounts greater than those recommended in the government's Dietary Guidelines for Americans. This effect may be amplified if you take more than one pill to get the minimum requirement of a specific micronutrient -- for instance, taking extra pills to get enough vitamin D may mean you're getting too much vitamin A. In some cases, high levels of vitamin A may be harmful.

Meanwhile, the benefits of multivitamins remain uncertain. The Women's Health Initiative concluded that postmenopausal women who took multivitamins did not have a lower death rate than others and were just as likely to develop cardiovascular disease or cancers of the lung, colon and rectum, breast, and endometrium. These results are consistent with findings from other studies. The National Institutes of Health (NIH) has said that there isn't enough evidence for a recommendation about taking multivitamins.

There's also been little or no evidence of protection against cardiovascular disease or cancers from a number of individual vitamin supplements, including vitamin E, vitamin C, beta carotene, and the B vitamin trio -- B6, B12, and folic acid. Research suggests that potential harm has been added to the mix. A Cochrane Collaboration review found that low-risk people in trials for a host of diseases who were given supplements of vitamin A, vitamin E, and beta carotene had a slightly higher death rate. And there's some evidence that excess folic acid (the synthetic version of folate, a vitamin found abundantly in vegetables, fruits, and grains) may be contributing to an uptick in colon polyps. Both observations warrant further study.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.