Are Supplements Killing You? The Problem With Vitamins, Minerals


In two recently published studies, researchers suggest that supplements can do more harm than good if taken in addition to a healthy diet


Most people understand that taking nutritional supplements that have unproven health effects is taking a gamble. Yet few realize that this may also be true for vitamin and mineral supplements.

Two recently published studies suggest that vitamin and mineral supplements can do more harm than good. One study uncovered a definite link between taking Vitamin E and an increased risk of prostate cancer. The other suggests the possibility that elderly women taking vitamin and mineral supplements were at a higher risk of early death, though the study's results are open to interpretation.

Taken together, both studies call into question the wisdom of taking vitamin and mineral supplements on top of a normal diet. It just might be too much of a good thing.


Vitamins, minerals, and other micronutrients are needed in small amounts for good health. Without them, diseases such as scurvy will develop (Vitamin C). Some of the effects of vitamin and mineral deficiency have been known for hundreds of years and the amounts needed to prevent deficiency are given as the recommended daily allowance (RDA), formerly the minimum daily requirement.

The current consensus is that a proper diet provides all the micronutrients that most people need.

In recent times, supplementing the diet with vitamins and minerals has shifted from trying to prevent deficiencies to taking higher amounts of them in an effort to enhance health. Studies indicate that about half of all people in the U.S. in the year 2000 were taking at least one supplement. And while the effects of too little of a vitamin or mineral are well known, there's been little opportunity to study the effects of higher levels of these substances on health.

Overdoses of vitamin A and D can occur and lead to health problems. Both are fat-soluble vitamins (as is vitamin E) and can build up in the body over time. But such overdoses are rare. And since excess water-soluble vitamins are excreted and don't build up in the body, overdoses of them are even rarer. But as with everything else, it's almost certain that the effects of vitamins and minerals on health follow an upside down U curve: too little is bad for health and so is too much. The two recent studies are fairly preliminary investigations into what constitutes too much.


The SELECT trial (the Selenium and Vitamin E Cancer Prevention Trial) was designed to determine the long range effect of selenium and vitamin E supplements on prostate cancer. Previous studies had hinted that both of these substances might offer protection against prostate cancer. But the trial found a 17 percent increase in the risk of developing prostate cancer in men who took 400 units of vitamin E daily, and no protection against developing prostate cancer from selenium.

Over 35,000 men from the U.S., Canada, and Puerto Rico were split into four groups in a randomized controlled study. One group took 400 International Units of Vitamin E per day, the second took 200 micrograms of selenium a day, the third took both vitamin E and selenium, and the fourth took only inactive placebo.

All men were 50 years or older and showed no initial signs of prostate cancer, as judged by a digital rectal examination and PSA level. Enrollment began in August 2001 and ended in June 2004.

Preliminary results from the study in 2008 showed an increased rate of prostate cancer among both the group taking vitamin E and the group taking selenium. While these increases were not statistically significant, the increase in the vitamin E group was nearly so. The trial had been designed to seek a protective effect from either vitamin E or selenium. It wasn't finding one and instead was finding evidence of possible harm. Because of this, subjects stopped taking the supplements in October 2008. They continued to be tracked for new cases of prostate cancer.

The recently published article included results as of July 2011. It found an increase in new prostate cancers among all three groups taking supplements, with the increase only significant in the vitamin E group. That group showed a 17 percent increase in the rate of prostate cancer compared to the placebo group.

The selenium group showed a nine percent increase and the group taking both selenium and vitamin E showed a five percent increase, increases that were not statistically significant and could have been caused by chance alone. The results of the group taking both vitamin E and selenium suggest that selenium somehow blunts the ability of vitamin E to increase prostate cancers.

The researchers don't offer a biological explanation for why vitamin E appears to increase the risk of prostate cancer. They do express concern that the rate of prostate cancer continued to rise even after subjects stopped taking vitamin E supplements, suggesting that harm continues for years afterwards. They also note a 2005 study that found that 50 percent of U.S. individuals over the age of 60 take vitamin E containing supplements and 23 percent of them are taking at least 400 IU of vitamin E per day. The SELECT study may give them a reason to reconsider this. The adult RDA for vitamin E is 22.5 IU a day.


The Iowa Women's Health Study looked at the effect of taking vitamin and mineral supplements on mortality on nearly 39,000 U.S. women aged 55 to 69 and used information collected from 1986 through 2008.

At the start of the study, 66 percent of the study subjects reported using at least one supplement. This increased to 85 percent in 2004, with 27 percent reporting use of four or more supplements.

The study examined the effect of taking 14 individual supplements and also a multivitamin. The researchers concluded that women who took any of six supplements or a multivitamin had a slightly higher risk of death over the study period:

  • Multivitamins were associated with a 2.4 percent higher risk of earlier death
  • Vitamin B6 gave a 4.1 percent higher risk
  • Folic acid gave a 5.9 percent higher risk
  • Iron gave a 3.9 percent higher risk
  • Magnesium gave a 3.6 percent higher risk
  • Zinc gave a 3 percent higher risk
  • Copper gave an 18 percent higher risk
  • Calcium gave a 3.8 percent lower risk of death

However, different types of statistical analyses markedly changed these results.

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