Although the reason why isn’t clear, studies have shown that among men of European ancestry, those with diabetes have a lower risk of developing prostate cancer than those without the condition. That got California researchers wondering whether that inverse relationship existed across other racial and ethnic groups.
To find out, they analyzed 5,941 cases of prostate cancer identified over 12 years in 86,303 European American, African American, Latino, Japanese American, and Native Hawaiian men in the Multiethnic Cohort Study, a prospective cohort study under way in Hawaii and Los Angeles. Participants completed an initial questionnaire about lifestyle factors, such as diet and physical activity, any medical conditions, and family history of common cancers. A short follow-up questionnaire sent in 2001 also asked about history of prostate-specific antigen (PSA) screening.
Researchers discovered that men with diabetes had a significantly lower risk of prostate cancer than nondiabetics across all populations, though the risk varied somewhat among the groups. They also found that average PSA levels were significantly lower in diabetics than in nondiabetics.
These conclusions suggest a biological link between the two conditions. Similarly, a Harvard study of 51,529 men published in March found that, for a man with diabetes, the risk of prostate cancer decreased over time. Men in that study were followed from 1986 to 2004. But a Swedish study that followed 10,564 men for 11 years on average concluded that there was no significant association between diabetes and prostate cancer risk. However, researchers noted that the relatively small number of diabetics in the study may have skewed the results.
SOURCES: Kasper JS, Liu Y, Giovannucci E. Diabetes Mellitus and Risk of Prostate Cancer in the Health Professionals Follow-Up Study. International Journal of Cancer 2009;124:1398–403. PMID: 19058180.
Wallström P, Bjartell A, Gullberg B, et al. A Prospective Swedish Study on Body Size, Body Composition, Diabetes, and Prostate Cancer Risk. British Journal of Cancer 2009;100:1799–805. PMID: 19436298.
Waters KM, Henderson BE, Stram DO, et al. Association of Diabetes with Prostate Cancer Risk in the Multiethnic Cohort. American Journal of Epidemiology 2009;169:937–45. PMID: 19240222.
Originally published September 2009; last reviewed February 24, 2011.