Science and Law
15th December 2011

Should you stop taking your vitamins?

Two vitamin-related studies have recently made a splash in the media. Both studies reported that taking extra doses of vitamins can do more harm than good.

Should you stop taking your vitamins?

Two vitamin-related studies have recently made a splash in the media. Both studies reported that taking extra doses of vitamins can do more harm than good.

Let’s take a closer look at the studies.

Vitamin E, Selenium, and Prostate Cancer

The SELECT trial was conducted by SWOG (an international network of research institutions) and involved more than 400 clinical sites in the United States, Puerto Rico, and Canada. Researchers investigated whether vitamin E and selenium (alone or in combination) could lower a man’s risk of developing prostate cancer. The findings showed that the vitamin users had a 17% higher risk of prostate cancer compared with the placebo group (Klein et al.). As a side note, this trial, which began in 2001 and included over 35,000 subjects, was stopped early in 2008 after a review of the data suggested no benefit, and an increased risk of prostate cancer and diabetes (Lippman, 2009). Overall, the increased risk for prostate cancer was statistically significant, and represents 11 more cases of prostate cancer in the supplement group per 1,000 men compared to the control group.

Dietary Supplements in Older Women

In a large observational study (The Iowa Women’s Health Study), older women who used common dietary supplements died at a higher rate than women who did not rely on supplements. Researchers followed 38,772 women (average age 62 at the start of the study), over a period of 19 years, during which 15,594 of them died. Those using multivitamins or supplements of iron, vitamin B6, folic acid or zinc were at an increased risk of death relative to those who did not take supplements. The findings indicate a 2.4% increase in risk for multivitamin users, a 4% increase associated with vitamin B6, a 5.9% increase for folic acid, and increases of 3 – 4% in risk for those taking supplements of iron, folic acid, magnesium and zinc. Interestingly, certain supplements, like vitamin A and vitamin D, had no effect, and calcium supplements tended to lower the risk (Mursu et al.).

So, should you stop taking your vitamins? Let’s look at the issues surrounding each of the studies.

The SELECT trial was a randomized controlled trial (the gold-standard for determining causation), however, some controversy has sprung up around the type of vitamin E that was used. There are multiple forms of vitamin E, and evidence to date has shown different functionality for these forms with respect to various endpoints. Importantly, the SELECT study used only one form of vitamin E (alpha-tocopherol), which has been suggested by others to be ineffective at preventing prostate cancer unless used along with the gamma-tocopherol version of vitamin E. Thus, because the SELECT trial only used alpha-tocopherol, the role of the other forms of vitamin E in prostate cancer prevention remains unknown. 

Interestingly, SELECT researchers are now measuring the amount of vitamin E, selenium, and other nutrients in the blood of participants when they joined the trial, to see if the effect of the supplements depended upon this baseline level of micronutrient. Others are looking at certain DNA changes (known as SNPs) to determine if a change in one or more genes could affect cancer risk or perhaps increase a man’s risk of developing prostate cancer while taking vitamin E.

Unlike SELECT, the Iowa multivitamin supplementation study was observational in nature. As with most observational studies, which are generally designed to look for correlations (and not causation), numerous factors other than supplement use might have affected the outcome. For example, since the study was conducted in older white women, and thus not representative of the general population, the findings may not be applicable to everyone. Furthermore, it is not known why the participants in this study started taking supplements in the first place. Was it because of a decline in their health or a preceding disease (e.g. heart attack)?  Another salient feature is that the form and quality of the vitamins were not standardized for the study. Taking vitamins that are potentially inactive or even toxic may limit any observed benefit. Other potentially confounding factors include hormone replacement therapy by the subjects. More of the subjects in the supplementation group were on hormonal therapy compared to the non-user group. In this case, it is not know how hormone therapy interacts with vitamin supplementation.

It seems the conclusion for now is that more studies are warranted and individuals should talk to their physician about the possible benefits and risks of any supplement they may wish to take.

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