Obesity was associated with an increased risk for prostate cancer in African-American men and that risk grew by nearly four times as body-mass index (BMI) increased, according to a new study. 

African-American men have the highest incidence of prostate cancer of any racial or ethnic group in the United States, as well as the highest rates of aggressive disease and prostate cancer death. 

Wendy E. Barrington, Ph.D., of the University of Washington School of Nursing and the Fred Hutchinson Cancer Research Center, Seattle, and co-authors compared the associations of obesity with prostate cancer risk between African-American and non-Hispanic
European-American
 men. The authors used data from 3,398 African-American and 22,673 non-Hispanic
European-American
men who had participated in the Selenium and Vitamin E Cancer Prevention (SELECT) Trial (2001-2011). Outcomes for the present analysis were total, low-grade (Gleason score less than 7) and high-grade (Gleason score greater than or equal to 7) prostate cancer incidence.

During a median follow-up of 5.6 years, 1,723 men developed prostate cancer (270 total cases among African-American men and 1,453 total cases among non-Hispanic 
European-American
 men). Overall, the study found a 58 percent increased risk for prostate cancer among African-American men compared with non-Hispanic 
European-American
men.

Obesity was not associated with risk for prostate cancer overall among non-Hispanic
European-American
 men but there was a significant association between obesity and the risk for total (both low and high grade) prostate cancer in African-American men. For example, being African-American increased the risk for prostate cancer across BMI categories, jumping from 28 percent among African-American men with a BMI less than 25 to 103 percent among African American men with a BMI of at least 35, according to the results.

For low-grade cancer, obesity was inversely associated with prostate cancer risk among non-Hispanic
European-American
men; those with a BMI of at least 35 had a 20 percent reduced risk compared with those non-Hispanic
European-American
men with a BMI less than 25. However, obesity was positively associated with the risk of high-grade prostate cancer among non-Hispanic
European-American
men.

Among African-American men, obesity was positively associated with risks for both low- and high-grade prostate cancer, according to the study results.

The authors note the reasons underlying their findings are unknown but they speculate that one explanation may be that the biological effects of obesity differ in African-American and non-Hispanic European-American men.

Citation: JAMA Oncol. April 16, 2015. doi:10.1001/jamaoncol.2015.0513.