Selenium, a trace element found in foods such as certain nuts, liver and kidneys, may prove to be an important nutritional supplement for preventing breast cancer - if a person is genetically predisposed to the disease.
The correlation is being studied by two University of Illinois at Chicago nutrition scientists. Alan Diamond, professor and head of human nutrition, and Ya Jun Hu, a research assistant professor, report on their latest findings in the June 15 issue of the journal Cancer Research.
"For over 20 years, animal studies have shown that tiny amounts of selenium in the diet can suppress cancer in several types of organs," said Diamond. "The animal data is very strong, but human data is just emerging."
How selenium might prevent cancer remains unknown, Diamond said.
"We believe there are certain proteins in mammalian cells that contain selenium that can mediate the protective effects, but proving that is difficult," he said.
Diamond and Hu's study focused on the role played in breast cancer by a selenium-containing protein called glutathione peroxidase - an enzyme that is selenium-dependent and functions as an antioxidant.
"The way we studied this was to look at a certain selenium-containing gene that encodes for selenium-containing proteins, then examine their nucleotide - or genetic code - makeup for differences," Diamond said. "We looked to see if there were differences in the frequency of versions of these genes both in tumor cells and from DNA from people who didn't have cancer."
The study compared the same genes from 517 cancer-free individuals with the genes contained in 79 breast cancer tissue samples provided under an approved protocol by Chicago-area medical centers.
Diamond said the study draws two major conclusions: that there is a difference in the frequency of different versions of the genes in tumors versus in people without cancer; and that these differences have a functional consequence suggesting that a person with a certain version of the gene may require more selenium in the diet to get the cancer-preventive benefits.
"Utimately, this might influence who would most benefit from having dietary supplementary selenium," he said.
Diamond thinks that by identifying what version of the gene a person has, selenium supplements may someday be prescribed accordingly.
"By having a 'fingerprint' in the gene that allows one to distinguish between genes that may be associated with a greater risk of cancer, we naturally start thinking about the potential for diagnosis," Diamond said. "Can we identify people who may be at risk of cancer? Can we use the changes that occur at this gene during cancer development to detect cancers as they are developing - perhaps faster than existing tests? Finally, can we use this as a marker to identify people who may be able to benefit most from taking selenium supplements?"
Diamond said at this point it is still too early to make recommendations about baseline levels of dietary selenium that would benefit most of the population.