June 26, 2009
Genetic Variants Govern Harm Or Benefit Of Selenium For Prostate

Guys worried about prostate cancer risk: Should you take selenium or eat Brazil nuts to boost your blood selenium? The benefits or risks of selenium depend at least in part on genetic variants of the enzyme manganese superoxide dismutase (SOD2).

BOSTON--Higher selenium levels in the blood may worsen prostate cancer in some men who already have the disease, according to a study by researchers at Dana-Farber Cancer Institute the University of California, San Francisco.

This is a pretty dramatic demonstration of the future value of nutrigenomics where you'll be able to tailor your diet to fit your genetic endowment. What would be a beneficial diet for some men looks to be harmful to others.

25% of the population have two copies of the A variant of the manganese superoxide dismutase (SOD2) gene and for them higher selenium probably lowers their risk of prostate cancer. But those with one or two copies of the V version of the gene are at greater risk from prostate cancer if they get more selenium.

A higher risk of more-aggressive prostate cancer was seen in men with a certain genetic variant found in about 75 percent of the prostate cancer patients in the study. In those subjects, having a high level of selenium in the blood was associated with a two-fold greater risk of poorer outcomes than men with the lowest amounts of selenium. By contrast, the 25 percent of men with a different variant of the same gene and who had high selenium levels were at 40 percent lower risk of aggressive disease. The variants are slightly different forms of a gene that instructs cells to make manganese superoxide dismutase (SOD2), an enzyme that protects the body against harmful oxygen compounds.

This result calls into question the wisdom of taking selenium if you already have prostate cancer.

The research findings suggest that "if you already have prostate cancer, it may be a bad thing to take selenium," says Philip Kantoff, MD, director of Dana-Farber's Lank Center for Genitourinary Oncology and senior author of the study that is published by the Journal of Clinical Oncology on its website now and later will be in a print journal. The lead author is June Chan, ScD, of the University of California, San Francisco.

So if you have SOD2 in AA form you probably would benefit from higher selenium. Personal genetic profiles are starting to become useful in daily life.

Simply having a high level of selenium was associated with a slightly elevated risk of aggressive prostate cancer. But the risk was much more strongly affected by the interaction of selenium levels and whether the patient had a certain variant of the SOD2 gene. Men with the highest selenium levels and the "AA" form of the SOD2 gene were 40 percent less likely to have been diagnosed with aggressive prostate cancer than the men with same gene form but low levels of selenium.

But for men carrying the "V" form of the gene, selenium had the opposite effect. In these men, those with the highest levels of selenium in their blood were about twice as likely to have an aggressive type of prostate cancer as their counterparts with low selenium levels, says Kantoff, who is also a professor of medicine at Harvard Medical School.

This isn't the only gene which influences whether a food is beneficial or harmful. Some people have genes that cause them to retain too much iron. Others lack enough of the enzyme lactase for breaking down lactose sugar in milk. We aer going to see a big flood of genetic research findings about many more genetic variants that change which foods best fit individual needs.

Share |      Randall Parker, 2009 June 26 11:52 PM  Aging Diet Cancer Studies

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