Now and again, a study is published that leads to a sea change in public opinion. If you’re a regular EBL reader, you already know how we feel about this. (While a single study provides some evidence about an issue, we should really consider all of the available evidence on a given topic before drawing any conclusions.)

Earlier this month, it wasn’t one study, but two.  Separate reports on the use of multivitamins and supplements among older women and the use of Vitamin E and selenium to prevent prostate cancer have led to a flurry of media reports about whether or not we, the general public, should take supplemental vitamins.

What does that mean for you?  We’ve done our best to dissect all of the evidence we can find.  Let’s start with the most recent studies.

First, researchers followed more than 38,000 older women for 25 years to track, among other things, their use of multivitamins and supplements. The study found that the risk of death among these women increased with long term use of multivitamins, vitamin B6, folic acid, iron, magnesium, zinc, and copper. They concluded there is “little justification for the general and widespread use of dietary supplements.”

In the second study, researchers followed more than 35,000 men over 10 years to determine whether taking vitamin E or selenium would decrease the risk of prostate cancer. In this study, the risk of cancer increased for men taking vitamin E, selenium, or both. This study also concluded there is little evidence for taking a supplement.

While these are both large, longitudinal studies, we thought it’d be prudent to check the other evidence available on supplements and talk to some Cornell nutrition professors about their interpretation of the data.

We started off at the Cochrane Collaboration, which has dozens of review on specific supplements for specific conditions. The most general report reviewed studies of supplements to prevent mortality. It reviewed 67 randomized trials with more than 200,000 participants, and found no evidence that supplements prolong life. It also concluded that Vitamin A, beta-carotene, and vitamin E may be harmful.

J. Thomas Brenna, Cornell professor of nutritional sciences, draws the same conclusions. “Human trials of so-called antioxidants have generally been neutral or shown harm, and these recent reports are consistent with their findings,” he said.

Brenna’s take on vitamins and supplements boils down to what he calls one of the oldest and most reliable mantras in biological science, “The dose make the poison.”  In other words, you can get too much of a good thing, and excess vitamin supplementation is no exception.

Patsy Brannon, also a professor of nutritional sciences, emphasized the need to consider your total intake of vitamins and minerals. 

“We know that those who take vitamin and mineral supplements tend to be consuming a healthier diet,” she said. “Further, many foods are fortified with minerals and vitamins such as ready-to-eat cereals and fruit justices.”

So who might benefit from a supplement and how to decide on what supplement to take and how much? 

“For those who routinely consume less than 1500 calories per day, it may be hard to consume all the vitamins and minerals in the amounts needed.  Then, a multivitamin-mineral supplement that provides only 100 percent of the recommended daily values for each of the nutrients in the supplement would be helpful,” she said.

Brannon pointed out a recent study published in the Journal of Nutrition that many adults are not meeting their nutritional needs.  Other evidence found only about 25 percent of American adults are following the recommended dietary guidelines.

The bottom line: Yes, supplements are important for specific deficiencies or when diets do not include a healthy variety of foods.  But the public as a whole may be overconsuming them to ensure health. When that happens, they may do some harm.