Why Obese Men Post Lower PSA Levels

Why Obese Men Post Lower PSA Levels
TUESDAY, Nov. 20 (HealthDay News) -- In recent years, doctorshave learned that they need to adjust the results of blood tests toproperly diagnose prostate cancer in obese men, but now researchers thinkthey know why.
It turns out that larger men have more blood, which dilutes the levelsof the protein called PSA -- a key indicator of prostate trouble.
The new study doesn't definitively prove why overweight and obese menwith prostate cancer tend to score lower on the PSA (prostate specificantigen) test, but it does give doctors an idea about what may be goingon, said study co-author Dr. Stephen Freedland, an assistant professor ofurology and pathology at Duke University.
"PSA is not a bad test for obese men. We just need to know how to useit," he said. "If we use it correctly, it will be just as good as innormal-weight men."
Prostate cancer strikes one in six men, mostly those over the age of65, according to the Prostate Cancer Foundation.
Older men often routinely undergo a PSA blood test that looks for anantigen made by the prostate that helps it function. The antigen leaksinto the bloodstream at a steady rate, and the amount is higher in menwith prostate cancer, Freedland explained.
Recent research has revealed that PSA levels are 20 percent to 25percent lower in overweight and obese men than in men of normal weight.This can translate into diagnostic problems with bigger men, Freedlandsaid.
"You may call him normal and not worry about him and wait another yearor two or longer, and that gives time for the cancer to grow," henoted.
According to Freedland, it's not clear if there's any impact on PSAlevels from being underweight.
In the new study, researchers tested a theory that the reason PSAlevels are lower in larger men is because the antigen gets diluted inlarger volumes of blood. "It's like taking a little bit of a drug andputting it in a cup of water versus a bowl of water," Freedland said.
The study authors looked at the records of about 14,000 men withprostate cancer who underwent removal of their prostates between 1988 and2006. The findings are published in the Nov. 21 issue of the Journal ofthe American Medical Association.
The researchers found that men who were fatter had larger bloodvolumes, which the study authors said supports their theory that dilutioncaused their PSA levels to lower.
The same thing could hold true for blood markers of other cancers,Freedland said. "As we develop blood tests for other cancers, we should bekeeping this in mind," he added.
However, Dr. Nelson Stone, a clinical professor of urology andradiation oncology at Mount Sinai School of Medicine, is skeptical of theresults, because the research just focused on men with advanced prostatecancer. That and other factors may have skewed the results, he said.
"I don't think they've proved their point," he said. But he added, "Weneed to be a little bit more careful when we evaluate a patient who islarger, and we look at his PSA and compare to a patient who is thinner.The PSAs are not the same."
More information
For advice on losing weight, visit the U.S.Food and Drug Administration.