Effects of Multivitamins

If your doctor says you lack certain nutrients, a multivitamin might be helpful. Multivitamins come in many varieties, so ask your doctor which will meet your needs. But for the general population, it's not clear what the effects of multivitamins are. The safest approach is to avoid multivitamins unless your doctor recommends them and to eat a balanced diet that supplies all the nutrients, including vitamins and minerals, that your body needs.

Effects

If you lack a particular nutrient, a multivitamin might be able to restore it. On the other hand, multivitamins might cause you to exceed your recommended daily intake of other nutrients. While this isn't a problem for some vitamins and minerals, excessive amounts of others might be dangerous. For example, excessive calcium intake can cause kidney stones and malabsorption of iron and zinc from food. General negative side effects of taking multivitamins are an upset stomach or an unpleasant taste.

Expert Insight

Little is known about the benefits and risks of taking multivitamins, so the U.S. National Institutes of Health convened an independent panel of experts in 2006 to study the issue. J. Michael McGinnis, who chaired the panel, said, "The bottom line is that we don't know for sure," whether multivitamins are benefiting the many Americans who take them, according to a 2006 report by the NIH.

Multivitamins and Medical Conditions

Although the panel recognized that certain vitamin and mineral supplements might be necessary for people with prevailing medical conditions -- such as age-related eye disease or pregnancy -- it said there was insufficient evidence for making a firm recommendation to the general population for or against the use of multivitamins to prevent chronic diseases, according to the NIH report.

Problem

A major problem is the difficulty of studying how multivitamins affect people. Confounding factors include the various types and amounts of nutrients found in different multivitamins, whether people follow recommended dosages and how much of each nutrient is also obtained through the diet, according to a review published in the January 2007 issue of the "American Journal of Clinical Nutrition." A further problem is that people who take multivitamins are more likely to have overall healthier lifestyles that include regular exercise and a healthy diet, according to the NIH report, so it's difficult to clarify the significance of the role of multivitamins in their health.