SOURCES: Wendy E. Barrington, Ph.D., assistant professor, school of nursing, University of Washington, and affiliate investigator, Fred Hutchinson Cancer Research Center, Seattle, Wash.; Alexander Kutikov, M.D., associate professor, urologic oncology, Fox Chase Cancer Center, Philadelphia, Pa.; April 16, 2015, online, JAMA Oncology
THURSDAY, April 16, 2015 (HealthDay News) -- Blacks have a higher risk of developing prostate cancer than whites, and for obese black men, their risk can quadruple as their weight goes up, a new study indicates.
The findings from this large study should lead to a redoubling of efforts to encourage obesity prevention among black men, said study lead author Wendy Barrington, an assistant professor in the school of nursing at the University of Washington.
"The main 'take-home' point for practicing physicians is to recognize that obesity has a different relationship to prostate cancer risk in African-American [men] compared to non-Hispanic white men," said Barrington.
Why this might be so is "really just speculation at this point," Barrington noted.
"We did account for many differences that could affect prostate cancer risk, such as access to care, and lifestyle factors, such as diet and physical activity," she said.
"But it could also be that there's actually a biological difference between African-American and non-Hispanic white men . . . It's something for further research," Barrington added.
However, a cancer specialist pointed out the study only established an association between race, obesity and cancer, not a direct cause-and-effect relationship.
The study results appear in the April 16 online issue of JAMA Oncology.
About six in 10 prostate cancer cases occur in men older than 65, the American Cancer Society notes. For reasons that remain unclear, it has long been known that at any age, blacks face a greater overall risk for the disease than other men. The study team noted that blacks also face the highest risk for aggressive prostate cancer and death.
To explore a possible connection between obesity and prostate cancer, investigators analyzed data collected between 2001 and 2011 by the Selenium and Vitamin E Cancer Prevention Trial.
The trial included nearly 3,400 black men and almost 22,700 white men, all cancer-free and age 55 and up at the start.
Medical histories were gathered, including information on smoking, diabetes, family history of prostate cancer, ethnicity, and education. Body mass index (BMI) was also assessed. BMI is a calculation of body fat based on height and weight.
A BMI of 25 and under is considered normal. Obesity is considered to be a BMI of 30, while a BMI of 35 or above is classified as severe obesity.
Over a follow-up of roughly 5.5 years, the study found a 58 percent increased risk for prostate cancer among blacks compared with whites.
In terms of weight, researchers found obesity raised risk in blacks as weight increased. For black men with a BMI of 25 or less, their risk for any prostate cancer was up 28 percent, while that risk jumped to 103 percent for blacks with a BMI of 35 or more.
Obesity among black men was also linked to greater risk of both aggressive and non-aggressive prostate cancer risk.
Compared with healthy-weight black men, severely obese blacks more faced a 122 percent increased risk for low-grade (slow-moving) prostate cancer. Their risk for high-grade (fast-moving) disease was 81 percent higher, the study found.
Obese white men, meanwhile, were found to face a 33 percent higher risk for aggressive prostate cancer compared with normal-weight whites, and no greater risk for slow-growing cancer.
In fact, obese whites appeared to face a 20 percent lower risk for slow-moving prostate cancer, relative to their healthy-weight peers, the researchers reported.
Obesity prevention efforts should address obstacles to healthy eating -- such as disparities in accessing healthier foods -- "without blaming the victim," Barrington said.
Dr. Alexander Kutikov, an associate professor of urologic oncology at Fox Chase Cancer Center in Philadelphia, cautioned that "the study only demonstrates a correlation between obesity and prostate cancer, and does not prove that weight loss in men who are obese would actually reduce their prostate cancer risk."
However, given the ongoing debate about the value of routine prostate cancer screening, "this study identifies obese men, especially those of African ancestry, as a high-risk population who may particularly benefit from screening," Kutikov said.
There's more on prostate cancer risk at the American Cancer Society.