The effect of obesity and lower serum prostate-specific antigen levels on prostate-cancer screening results in American men

OBJECTIVE To determine if lower serum total prostate specific antigen (PSA) levels in obese American men affect prostate-cancer screening results, as an increased body mass index (BMI) is inversely associated with PSA level, but the effect of this association on PSA screening results for prostate cancer is unknown. SUBJECTS AND METHODS We analysed the most recent National Health and Nutrition Examination Surveys (NHANES 2001-2002, 2003-2004, and 2005-2006), a nationally representative cross-sectional sample of non-institutionalized adults aged >= 20 years. Logistic regression was used to estimate the odds of an 'abnormal' PSA level (4.0 or 2.5 ng/mL) based on BMI categories of normal (18.5-24.9 kg/m2), overweight (25-29.9) and obese (30-39.9) in men who were eligible for prostate-cancer screening with serum total PSA tests (age 40-75 years, BMI 18.5-39.9 kg/m2, PSA < 20 ng/mL). RESULTS In all, 3152 participants with no known prostate cancer, representing 46 million American men, were eligible for prostate-cancer screening. After controlling for age and race, there was a statistically significant trend of a lower likelihood of having a serum total PSA level of >= 4.0 ng/mL with increased BMI. When men were stratified by race, this effect was apparent only in white non-Hispanic men, with obese men in this group having a 46% lower likelihood of having an 'abnormal' PSA level (odds ratio 0.54, 95% confidence interval 0.31-0.91; P = 0.024) than those with a normal BMI. There was no observable trend in either African-American or Hispanic men. In addition, there was no observable trend with a serum total PSA threshold of 2.5 ng/mL, regardless of race. CONCLUSIONS Obese white non-Hispanic men are about half as likely as those with a normal BMI to have a PSA level of >= 4.0 ng/mL. These results might affect prostate-cancer screening with serum total PSA. Further studies are needed to better define the association of BMI and PSA in racial minority subgroups.