Selenium and Prostate Cancer
Data from a recently published study* indicate that, although there does not appear to be an overall connection between an elevated selenium concentration in a man’s bloodstream and his risk of developing prostate cancer, some populations of men with higher selenium concentrations do seem to have a reduced risk for the disease.
(Selenium is a mineral present in widely varying concentrations in soil – and therefore in the plants and animals that humans may consume.)
Selenium appears to work with other compounds
A team from the Fred Hutchinson Cancer Research Center and the National Cancer Institute conducted a one-time screening of 724 prostate cancer patients and 879 control subjects.
The researchers gathered baseline data by obtaining blood samples, collecting demographic information and medical histories, and asking each man detailed questions about his diet, exercise habits, alcohol and tobacco use, and vitamin E intake, among other things.
All 1,603 participants also underwent standardized PSA screenings at baseline and during follow-up – a unique feature of the study, says primary investigator Ulrike Peters, PhD, because it reduced bias. The men were then followed for up to eight years.
The results indicated no association between the men’s blood selenium concentrations and their chances of developing prostate cancer. However, men with higher concentrations of selenium who also reported multivitamin use and/or a greater-than-28 IU daily intake of vitamin E had a 40 percent lower risk of developing prostate cancer compared with men with low serum selenium concentrations.
Additionally, data showed that smokers with high selenium concentrations had a significantly reduced risk of getting prostate cancer – 50 percent. This finding is especially interesting, Peters says, because selenium reduces oxidative stress, while smoking increases it.
Although the study yielded no real surprises, she says, it did strengthen the team’s hypothesis that there is an interaction between selenium and compounds related to oxidative stress in reducing prostate cancer risk.
“The jury is still out”
Peters says this about the recommended selenium intake.
“The upper limit for selenium intake is 400 micrograms a day, with 55 micrograms being the recommended intake,” Peters says. “But there’s discussion about whether that’s enough to prevent chronic diseases like cancer; clinical trials using 200 micrograms a day have found evidence of cancer prevention.”
“Anything can be a toxin when consumed in excess,” she adds, “and we know from studies done in China that people with very high selenium concentrations can experience hair and nail brittleness and loss, gastrointestinal disturbances, skin rash, garlic breath odor (caused by selenium compounds), fatigue, and irritability.”
As for vitamin E, Peters says, one Finnish study linked high E intake with an increase in mortality from hemorrhagic stroke – “but that could have been because the participants were all smokers.”
They upshot is that men should not exceed the recommended daily intake of selenium without speaking with their doctors.
Peters says. “Overall, the jury is still out about selenium.”
* Peters U, et al., Serum Selenium and Risk of prostate cancer – A Nested Case-Control Study. Am J Clin Nutr. 2007 Jan;85(1):209-17.