Scientists reporting in the September issue of Cancer Epidemiology, Biomarkers & Prevention say that adults with low blood levels of the mineral selenium are more likely to develop bladder cancer. The lower your levels of selenium, the higher your risk.
Selenium is a trace mineral found in soil. Dietary sources of selenium include plant foods and meats from animals that grazed on grain or plants grown in selenium-rich soil. The nutrient is also found in certain nuts. For example, brazil nuts often contain an abundance of selenium.
The body uses selenium to make selenoproteins. Many selenoproteins function as antioxidants, which prevent cellular damage. Some studies have suggested that selenium can help protect against certain cancers, but clinical trials on selenium supplementation have yielded conflicting results.
For the current study, Nuria Malats, MD, PhD, leader of the Genetic and Molecular Epidemiology Group of the Human Cancer Genetics Program at the Spanish National Cancer Research Center, and colleagues combined information from seven previously published studies to conduct their research. They reviewed selenium levels taken from blood samples and toenail clippings and determined each patient's risk of developing bladder cancer. The analysis included patients mostly from the United States and some patients from Europe.
A 39% decrease in bladder cancer risk was associated with the highest levels of selenium.
The protective benefit of selenium was seen mostly in women. Researchers believe this may be because of differences in how men and women's bodies break down and remove the mineral.
“Although our results suggest a beneficial effect of high selenium intake for bladder cancer risk, more studies are needed to confirm these findings before an enforcement of high selenium intake is recommended,” Malats says in a news release.
The recommended daily allowance (RDA) for selenium for adults is 55 micrograms per day. Women who are pregnant or breastfeeding may require higher amounts. Most American diets provide the recommended amount of the mineral, according to the National Institutes of Health.
Before adding more selenium to your diet, talk to your doctor. Too much selenium can be unhealthy and may lead to a condition called selenosis. Symptoms include stomach upset, hair loss, garlic breath odor, white spots on the nails, irritability, fatigue, and mild nerve damage. The Institute of Medicine of the National Academy of Sciences says the highest amount of selenium that adults can take safely without endangering their health is 400 micrograms a day. This is called the tolerable upper intake level (UL).