Taking dietary supplements is not without risk. While many people believe that that taking dietary and herbal supplements is good for our health, the truth is that they aren’t benign. Supplements, whether theu are in the form of pills, lozenges, drinks or powders, they may have strong effects or our health. What’s more, supplements can also interact with prescription medicines, which can lead to potentially dangerous – and lethal – reactions.
A multi-center study led by Fred Hutchinson Cancer Research Center has found that high-dose supplementation with both the trace element selenium and vitamin E increase the risk of high-grade prostate cancer. But more importantly, the researchers found that this risk depends upon a man’s selenium status before taking the supplements.
The bottom line: The study showed no benefits to any men from either selenium or vitamin E supplements, and for significant proportions of men in the study these supplements were harmful!
These findings, published in the February 21, 2014 issues ofJNCI – Journal of the National Cancer Institute, are based on data from the Selenium and Vitamin E Cancer Prevention Trial, or SELECT. The SELECT-trial is a rigorously executed clinical trial to see if selenium or vitamin E or both substances could help prevent prostate cancer when taken as dietary supplements.
The randomized and placebo-controlled trial conducted by the SWOG cancer research cooperative group that involved more than 35,000 men (non?African American men at least 55 years of age and African American men at least 50 years of age) in United States, including Puerto Rico, and Canada.
The study sought to determine whether taking high-dose vitamin E (400 IU/day of all rac ?-tocopheryl acetate) and/or selenium (200 ?g/day from L-selenomethionine) supplements could protect men from prostate cancer. The SELECT-trial was designed as a large, simple trial that conformed closely with community standards of care.
Increased risk
The trial, which began in 2001 and was designed to last 12 years, stopped early, in 2008, because it found no protective effect from selenium and there was a suggestion that vitamin E increased risk. While use of the study supplements stopped, men were still followed and after an additional two years the men who took vitamin E had a statistically significant 17% increased risk of prostate cancer.
Selenium supplementation increased cancer in men with high selenium status at baseline. However, when the study started, there was some evidence that selenium supplementation would not benefit men who already had an adequate intake of the nutrient. For that reason, researchers measured the concentration of selenium in participants’ toenails and planned to test whether selenium supplementation would benefit only the subset of men with low selenium status at baseline. Instead, they found that taking selenium supplements increased the risk of high-grade cancer by 91% among men with high selenium status at baseline. When selenium supplements were taken by men who had high selenium status to begin with, the levels of selenium became toxic.
Low selenium status at baseline
The study also found that only a subgroup of men was at increased risk of prostate cancer from taking vitamin E. Among men with low selenium status at baseline, vitamin E supplementation increased their total risk of prostate cancer by 63% and increased the risk of high-grade cancer by 111 percent. This explained one of the original SELECT findings, which was that only men who received vitamin E plus a placebo pill, and not those who received both vitamin E and selenium, had an increased prostate cancer risk. Selenium, whether from dietary sources or supplements, protected men from the harmful effects of vitamin E.
“Many people think that dietary supplements are helpful or at the least innocuous. This is not true,” said corresponding and first author Alan Kristal, Dr.P.H., a faculty member in the Public Health Sciences Division of Fred Hutch. “We know from several other studies that some high-dose dietary supplements ? that is, supplements that provide far more than the daily recommended intakes of micronutrients ? increase cancer risk. We knew this based on randomized, controlled, double-blinded studies for folate and beta carotene, and now we know it for vitamin E and selenium.”
The data for the current analysis compared the effect of selenium and vitamin E, taken either alone or combined, on prostate cancer risk among 1,739 men who were diagnosed with prostate cancer and, for comparison purposes, a random sample of 3,117 men without prostate cancer who were matched to the cases by race and age.
Bottom line: no benefits…
The bottom line: The study showed no benefits to any men from either selenium or vitamin E supplements, and for significant proportions of men in the study these supplements were harmful. “These supplements are popular ? especially vitamin E ? although so far no large, well-designed and well-conducted study has shown any benefits for preventing major chronic disease,” Kristal said.
…only risks
“Men using these supplements should stop, period. Neither selenium nor vitamin E supplementation confers any known benefits ? only risks,” he continued. “While there appear to be no risks from taking a standard multivitamin, the effects of high-dose single supplements are unpredictable, complex and often harmful. Taking a broad view of the recent scientific studies there is an emerging consistency about how we think about optimal intake of micronutrients. There are optimal levels, and these are often the levels obtained from a healthful diet, but either below or above the levels there are risks.”
In an accompanying editorial in JNCI, Paul H. Frankel, Ph.D, et al. discusses the potential biological mechanisms behind the findings by Kristal et al. Frankel writes: “These intriguing results stimulate discussion on a variety of points.” The editorialists propose some additional considerations regarding the specific selenium and vitamin E formulations, baseline selenium levels in men in different countries, and prevention considerations.
For more information:
[1] Lippman SM, Goodman PJ, Klein EA, Parnes HL, Thompson IM Jr, Kristal AR, et al. Designing the Selenium and Vitamin E Cancer Prevention Trial (SELECT).J Natl Cancer Inst. 2005 Jan 19;97(2):94-102 [Article][PubMed]
[2] S0000 Selenium and Vitamin E in Preventing Prostate Cancer (SELECT) NCT00006392 [Study Record Detail][NCI Info]
Photo: Alan Kristal, Dr.P.H., is on the faculty of the Public Health Sciences Division at Fred Hutchinson Cancer Research Center in Seattle. Courtesy: Fred Hutchinson Cancer Research Center.
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