Obesity may affect PSA levels, delay cancer diagnosis

Nancy Ferrari

Senior editor, Harvard Health

Obesity has been linked to death from a variety of cancers, including colon and breast cancers. The biological impact of obesity shoulders some of the blame, but excess body fat can also interfere with imaging tests and hinder physical examination. Multiple studies have also found that obese men have lower PSA concentrations than those with healthier weights. Why? One theory is that obese men simply have less hormonal activity. Recently, a team of researchers tested another hypothesis: obese men have a higher volume of plasma in their circulation, essentially diluting the concentration of PSA.

The researchers tested the idea in nearly 14,000 men, drawn from three different patient databases, all of whom had had a radical prostatectomy. They found that obese men not only had lower PSA values on average, but also a greater volume of plasma. The PSA mass — the actual amount of PSA in the blood — was similar to that in non-obese men. Given the greater volume of fluid in the blood, PSA concentration dropped, yielding lower PSA values during screening.

With seemingly low PSAs, fewer obese men have prostate biopsies, leaving their cancers undetected until they are larger, and thus more difficult to treat. However, the degree to which that contributes to worsened outcomes, the researchers say, remains to be determined.

SOURCE: Banez LL, Hamilton RJ, Partin AW, et al. Obesity-Related Plasma Hemodilution and PSA Concentration Among Men with Prostate Cancer. Journal of the American Medical Association 2007;298:2275–2280. PMID: 18029831.

Originally published April 2009, last reviewed March 2, 2011.

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