On top of a healthy diet, taking daily supplements can be an easy way to ensure your body gets enough of the vitamins and minerals it needs to function properly. It's also reasonably common: According to a recent study from the Centers for Disease Control and Prevention (CDC), 57.6 percent of U.S. adults had used one of the pills at any point in the past 30 days. But just like over-the-counter medicine, it's crucial to follow instructions whenever you're taking them to make sure you're not overdoing it. Research has shown that taking too much of one supplement in particular could increase the risk of one type of cancer. Read on to see why you should double-check your daily dosages.
Taking too much selenium and vitamin E raises your risk of cancer considerably.
According to research, it turns out there can be too much of a good thing when it comes to taking a selenium and vitamin E supplement. In one study published in the Journal of the National Cancer Institute in March 2014, researchers analyzed data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT). In total, the team used data from toenail samples collected from 31,117 men to explore whether baseline selenium levels in the body could affect prostate cancer risk.
Results found no correlation between existing levels of selenium or vitamin E in the body and prostate cancer risk. However, the researchers did make a connection between men with high levels of selenium in their systems who took a selenium supplement—whether alone or in combination with vitamin E—finding that such patients were twice as likely to develop high-grade prostate cancer than patients who were taking a placebo, Nature reports.
Taking a vitamin E supplement alone also raised the risk of cancer in some patients.
But there wasn't just a connection formed between taking a selenium supplement and the risk of prostate cancer. Results also found that just patients who had low baseline selenium levels in their systems and took vitamin E supplements alone were 111 percent more likely to develop high-grade prostate cancer than patients taking a placebo during the study.
Researchers also found that men who started with high selenium levels were no more likely to develop prostate cancer than men who began with low levels. The team says this establishes that added selenium in supplement form and not from food was the reason for the increased cancer risk.
The researchers concluded that there was more risk than benefits to taking high-dose supplements.
The researchers came to a stark conclusion that high dosages of any vitamin or mineral supplements are ill-advised at best. "We found there's no benefit for anyone," Alan Kristal, MD, the lead author of the study and a faculty member in the Public Health Sciences Division at Fred Hutchinson Cancer Research Center, said in a statement. "All we did find was a heightened risk. I'm now willing to go on the record and say that there is no evidence that high doses of supplements of anything are good for you."
Instead of attempting to fill gaps in your diet with daily pills, Kristal recommends eating healthy as a means of getting your vitamins and minerals. "The micronutrients in food are at a level that you need," he advised.
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Outside experts view the data as a sign that high-dose supplements should be reconsidered.
In response to the study, other experts said the results were enough evidence to consider avoiding using the popular daily pills altogether. "I counsel all of my patients to absolutely avoid any dietary supplements that contain selenium or vitamin E—including multivitamins," Marc Garnick, MD, prostate cancer expert and clinical professor of medicine at Harvard Medical School, an oncologist at Beth Israel Deaconess Medical Center, and editor in chief of Harvard's Annual Report on Prostate Diseases, said to Harvard Health Publishing.
"The new data are very troubling, and emphasize that supplements can cause real and tangible harm," Garnick added. "Any claims of benefits from dietary supplements must be ignored unless large, controlled, and well-conducted investigations confirm such benefits—which I believe will be a very rare occurrence."