Then patients are overweight, it is more difficult for doctors to detect prostate cancer. That's the conclusion of a study that found a higher body mass index (BMI) was associated with lower prostate specific antigen (PSA) levels. Higher PSA scores often indicate prostate cancer.
Dr. Ian Thompson, lead author, and his colleagues tested the PSA levels of almost 2,800 men who didn't have prostate cancer. They measured their height and weight and gathered information on race, age and lifestyle factors, such as dietary habits and supplement use.
They found that regardless of age or race, when BMI went up, PSA levels decreased.
The authors say they don't know exactly why higher BMIS would affect PSA scores, but they suspect that PSA is suppressed in heavier men because they have lower testosterone levels. According to Thompson, PSA production is sensitive to testosterone.
These findings may help explain why overweight men have been found to have an increased risk of death from prostate cancer in previous studies.
"Lower testosterone may be artificially lowering PSAs, and may be delaying diagnosis. That delay may be why obesity is associated with a higher risk of mortality after treatment," Thompson says.
Study co-author Jacques Baillargeon, an associate professor of epidemiology at the Center for Epidemiology and Biostatistics at the University of Texas Health Science Center, agrees. Higher BMIS "may have caused delayed disease ascertainment, which means men are being diagnosed at a later stage, when they may have more aggressive disease," she explains.
Thompson says the study shows that obesity and other factors that modify PSA "should probably be taken into account when you evaluate a man's risk of prostate cancer."
Dr. Christopher Lee, a urologist at New York University Medical Center, agrees. He says, "This study suggests that if you are obese, perhaps we should look at lower levels of PSA with more scrutiny, and perhaps (you should) be more aggressively pursued in terms of having another PSA test or biopsy."
Because early prostate cancer generally exhibits no symptoms, doctors rely on two screening tools—the PSA test and digital rectal exams (DRES).
However, some studies, including one by Thompson, have suggested the PSA test misses many cancers.
Still, Thompson says, "As a cancer-screening test, PSA is remarkably good." But the results of the test are not black and white. "PSA functions like blood pressure or cholesterol screenings—the higher in the range, the higher the risk. If you have a very low PSA, your risk is low, but not nonexistent. Can you have a heart attack with low cholesterol? Yes. Can you have high cholesterol and smoke and live to 95? Sure," Thompson says. But those scenarios are the exception rather than the rule. "PSA gives you a good handle on your risk," he says.