High BMI linked to low PSA levels, could mask prostate cancer
MedWire News: Obesity is associated with low prostate-specific antigen (PSA) levels and a slow rate of change in prostate-specific antigen over time, threatening the timely detection of prostate cancer in obese men, say US researchers.
Their study showed that having a body mass index (BMI) of at least 30 kg/m2 was also associated with having a large prostate volume, increased plasma volume, and increased age-adjusted changes in plasma volume over time, indicating that hemodilution may be affecting PSA levels in these men.
"These findings suggest that men with higher BMIs may be less likely to be screened for prostate cancer, because of consistently lower PSA levels over time," say Lauren Wallner (University of Michigan, Ann Arbor) and colleagues.
"It is therefore possible that fewer cancers are then detected in obese men due to their larger prostate size or that the diagnoses are delayed, resulting in more aggressive disease at diagnosis," they add in the journal Cancer Epidemiology Biomarkers and Prevention.
The team measured the BMI, prostate volume, and PSA levels of 545 men aged 40-79 years during 8 rounds of biennial follow-up from 1990, resulting in approximately 15 years of accumulated data.
Overall, obese men (n=141) had lower mean baseline PSA levels than men who were not obese (BMI <30 kg/m2; n=404), at 1.1 versus 1.4 ng/ml.
Wallner and team report that baseline obesity was weakly but inversely associated with baseline PSA levels, and that men who were obese at baseline had a lower age-adjusted mean annual percent change in PSA than did men who were not obese, at 3.04% versus 3.79% per year.
Obesity at baseline was also positively associated with prostate volume: obese men had a higher mean annual percent change in volume compared with non-obese men, at 2.48 versus 2.20 ml per year. Obese individuals also had higher age-adjusted mean plasma volumes at baseline (3.69 vs 3.33 l) and smaller mean annual changes in plasma volumes (0.001 l/year versus 0.005 l/year), compared with their non-obese counterparts.
Finally, after accounting for predicted annual percent PSA changes and intercepts, prostate volume, and BMI, and the rates of change of volume and BMI, obesity at baseline was significantly inversely associated with the rate of change of PSA over time.
"Overall, the findings from our study, taken together with findings from previous studies, suggest that prostate cancer may be less likely to be detected in obese men partly due to the influence of BMI on rate of prostate volume growth and the hemodilution of PSA," conclude Wallner et al.
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By Sarah Guy