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Diabetes protects against prostate cancer

ATLANTA, GEORGIA. The possible protective effect of diabetes against prostate cancer has been investigated once more, this time in a prospective study. Earlier studies have shown a reduction in risk of 10 to 40 per cent, and some suggest that diabetes is protective only several years after diagnosis. Researchers from the American Cancer Society used data on a group of 72,670 men from the Cancer Prevention Study II Nutrition Cohort. Information on diabetes and prostate cancer was gathered in 1982, 1992, 1997, 1999 and 2001. Prostate cancer was diagnosed in 5,318 men (7.3 per cent), who tended to be older and with a higher BMI.

The researchers found that overall; diabetes reduced the risk of prostate cancer by 33 per cent once age, race, education and prostate-specific antigen testing were taken into account. However, risk was significantly increased (by 23 per cent) in the first three years after diabetes diagnosis, compared with non- diabetic men, and only began to be protective after four years. The protective effect remained consistent when stage or grade of prostate cancer at diagnosis was examined. These results are consistent with the hypothesis that diabetes is associated with reduced risk of prostate cancer but only several years after diagnosis of diabetes, say the authors. The protective effect may be due to the reduced insulin levels found in men who have been diabetic for some time, as prostate cancer has been linked to high circulating levels of insulin.

The findings in the present study are consistent with results from a Health Professionals Follow-up Study, which also found an increased risk following diagnosis of diabetes and a protective effect after several years. In this study, prostate cancer risk was lowest 10 years after diabetes diagnosis, a reduction of 46 per cent. On the other hand, a recent case-control study within the US Physicians’ Health Study found a reduction in risk of 36 per cent, but with no link to the time since diabetes diagnosis.
Rodriguez, C et al. Diabetes and Risk of Prostate Cancer in a Prospective Cohort of US Men. American Journal of Epidemiology, Vol. 161, January 2005, pp. 147-152

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