The trace element selenium may prove to be an important nutritional supplement for preventing breast cancer if a person is genetically predisposed to the disease, suggest researchers in the US.
The team from University of Illinois at Chicago propose that people prone to breast cancer have different versions of certain genes. These people may need more selenium to help prevent the onset of cancer, they report.
Selenium, which is found in foods such as certain nuts, liver and kidneys, has long been linked with reduced risk of various cancers, with recent research showing its potential to ward off skin cancer.
"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 Alan Diamond, professor and head of human nutrition at the University of Illinois. "The animal data is very strong, but human data is just emerging."
However, science has not yet explained how selenium might prevent cancer, 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.
The study, published in the 15 June issue of Cancer Research, 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 tumour 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 centres.
Diamond concludes that there is a difference in the frequency of different versions of the genes in tumours compared to in people without cancer. 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, claims Diamond.
The researchers believe that the findings could help identify those who would most benefit from taking supplementary selenium - depending on 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?"
The researcher stressed that it is still too early to make recommendations about levels of dietary selenium that would help the majority of people. The research shows the increasing role of genetics in nutrition research - soon the two may be inseparable.