According to a new analysis of an earlier study, vitamin E may not increase the risk of prostate cancer among men with high selenium status but may elevate the risk in men with low levels. On the contrary, other studies have shown that increased intakes of vitamin E may prevent prostate cancer.
Based on the data of the Selenium and Vitamin E Cancer Prevention Trial (SELECT), the study investigated effects of selenium and vitamin E supplementation on prostate cancer conditional upon selenium status at the beginning of SELECT (1). The secondary analysis showed that vitamin E supplementation (alone) had no effect on prostate cancer among men with high selenium status (concentration in toenail) but increased the risks of total, low-grade, and high-grade prostate cancer among men with lower selenium status. Selenium supplementation did not benefit men with low selenium status but increased the risk of high-grade prostate cancer among men with high selenium status.
The researchers concluded that men should avoid selenium or vitamin E supplementation at doses that exceed recommended dietary intakes. The SELECT trial, which was ended in 2008, did find an increased risk in prostate cancer among men who received vitamin E supplementation (400 IU alpha-tocopherol per day) for 7 to 12 years (2). Among the 35,533 healthy men older than 55 years, 529 cases of prostate cancer were diagnosed in the placebo group vs. 620 cases in the vitamin E group (a 17% increased risk). Neither sele- nium (200 μg/day) nor vitamin E, alone or together prevented prostate cancer. The hypotheses underlying SELECT, that selenium and vitamin E individually and together decrease prostate cancer incidence, derived from epidemiologic and laboratory evidence.
The earlier Alpha-Tocopherol Beta-Carotene (ATBC) trial had reported a 35% reduction for prostate cancer in 29,133 male smokers, between 50 to 69 years of age, who received vitamin E supplements (50 mg alpha-tocopherol per day) for 5 to 8 years (3). A recent meta-analysis of prostate cancer intervention trials repor- ted that every 25 mg/L (5.8µmol/L) increase in blood alpha-tocopherol levels was associated with a 21% de- crease in prostate cancer risk (4). This is consistent with the ATBC trial which reported a significant decrease in mortality rate with serum alpha-tocopherol concentrations increasing to 30 µmol/L. According to intake surveys, 70% of US males between 51 to 70 years have serum alpha-tocopherol concentrations below
30 µmol/L and almost 100% are not consuming the recommended 15 mg vitamin E per day (5).
Regarding the different outcomes between the studies ATBC and SELECT, the researchers commented that SELECT only considered the vitamin E intakes of the participants via supplement vs. placebo intakes. The actual vitamin E status of the participants based on their blood vitamin E concentrations were measured in the ATBC trial but not in SELECT. Advice on vitamin E supplementation should be based on nutrient status. It is known that most vitamin E intervention trials were conducted in people with much better vitamin E status than the average American, the scientists added. To have evidence-based guidance, more research on the relationship between vitamin E status and health is needed.