Weight, wait, don’t tell us (what we don’t want to hear)

Grace Lu-Yao and colleagues have posted an interesting “Beyond the Abstract” commentary on the UroToday web site in relation to recent data about the associations between obesity and prostate cancer in America.

Data have suggested that obesity may both lower the risk for the initial development of prostate cancer and increase the risk of prostate cancer progression and death. On face value, this makes little sense, and Dr. Lu-Yao and her colleagues set out to see if they could help to clarify the apparent paradox.

In a recently published study, Parekh et al. were able to show that obese men actually have lower prostate biopsy rates than lean men. To do this, they studied testoterone data from the men participating in the Third National Health and Nutrition Examination Survey (NHANES III; n = 845); PSA data from men participating in NHANES 2001-2004 (n = 2458); and prostate biopsy rates in the National Health Interview Survey (NHIS 2000; n = 4789). They were able to show that:

  • Testosterone concentrations were inversely associated with obesity in NHANES III.
  • Among the participants in NHANES 2001-2004, obese men (with a body mass index [BMI] >35) were less likely than lean (BMI < 25) to have PSA concentrations that reached 4 ng/ml or higher.
  • Among NHIS participants
    • All BMI groups had similar rates of PSA testing.
    • 11 percent of men with BMI >30 had PSA levels of ≥ 4 ng/ml.
    • 16 percent of men with BMI < 25 had PSA levels of ≥ 4 ng/ml.
    • The biopsy rate among men with BMI >30 was 4.6 percent.
    • The biopsy rate among men with BMI < 25 was 5.8 percent.

In other words, obese men are less likely than non-obese men to have a PSA that meets historic levels suggesting the need for a biopsy; as a consequence obese men are less like to actually have a biopsy than men of standard BMI. Of course if one doesn’t have a biopsy, one isn’t going to get diagnosed with prostate cancer.

Yu-Lao and her colleagues suggest that — among obese men — we should not conclude that a historically lower rate of detection of prostate cancer equates to a lower risk for prostate cancer.

In their “Beyond the Abstract” commentary, Yu-Lao and her colleagues place considerable emphasis on the public health and clinical implications of this finding, and recommend that it might help to include BMI data in evolving tools for prediction of risk for a positive biopsy, such as the Prostate Cancer Risk Calculator. They note that more than 75 percent of American men aged 40+ years are now classified as obese (BMI > 35) or at least overweight (BMI ≥ 25). They also point out that, on the basis of the data above, the impact of obesity on prostate cancer screening and biopsy can potentially influence the stage of prostate cancer diagnosis and thus the incidence and mortality rate associated with this disease.

Of course the other possible take-away from this study is that if obesity is in fact reducing the likelihood of diagnosis of prostate cancer, then that’s just one more reason for dealing with one’s obesity — which has now been associated with increased risk for a multitude of acute and chronic illnesses. From a public health point of view, if we do not find a way to deal with obesity in America, we are soon going to be seeing US male life expectancy drop for the first time since data have been available. On the upside, a decline in US male life expectancy between now and 2080 would potentially correlate to a overall decline in the incidence of prostate cancer compared to what is currently predicted.

2 Responses

  1. I seem to recall a study that demonstrated that obese men tended to have lower PSA results because of the greater quantity of blood circulating in their systems which “watered down” the proportion of PSA?

    Or is my memory failing me – AGAIN?

  2. That was indeed an hypothesis postulated on the basis of at least one study.

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