April 23, 2015. African American men have the highest rates of prostate cancer incidence and mortality in the United States. For the past twenty years cancer researchers have worried about this and researched various causal factors. Now a large study suggests obesity may play an important role in what specialists in disparities in prostate cancer risk are calling the "African-American race effect.
The first first nationwide prospective study to examine the impact of "race effect" on prostate cancer risk was published April 16 in JAMA Oncology. Alan Kristal, DrPH at Fred Hutchinson Cancer Research Center and Wendy Barrington, Ph.D., M.P.H at the University of Washington approached the problem by looking at how race and obesity jointly affect this risk.
Obesity has a number of adverse health effects on people of all races. But when it comes to prostate cancer, Barrington and Kristal discovered, obesity affects African American men differently than the rest of the US male population.
The "Race Effect" on Prostrate Cancer
In particular, in black men it substantially increases risks of developing prostate cancer and risks of dying from the disease. The effect on prostate cancer risk in African-American is profoundly different as compared to non-Hispanic white men.
Obesity in white men moderately reduces the risk of low-grade cancer and only slightly increases the risk of high-grade cancer. But in black men, obesity substantially increases the risk of both low- and high-grade prostate cancer.
Black men who are obese--a body-mass index of 35 or higher--had a 122 percent increased risk of low-grade and an 81 percent increased risk of high-grade prostate cancer compared to those who were of normal weight (a BMI of 25 or lower).
In contrast, among non-Hispanic white men, those who are just as obese had a 20 percent reduced risk of low-grade and only a 33 percent increased risk of high-grade prostate cancer compared to those of normal weight.
“For unknown reasons, African-American men have a much higher risk of prostate cancer than non-Hispanic white men," Kristal said. "Different effects of obesity might explain at least some of the difference in risk and, more importantly, preventing obesity in African-American men could substantially lower their prostate cancer risk.”
According to the National Cancer Institute, black men have the highest prostate cancer rates of any racial or ethnic group in the U.S.. They tend to get more aggressive forms of this cancer and are more than twice as likely to die of the disease as compared to non-Hispanic white men.
These elevated risks for African-American men are due to both social disadvantage, such as access to resources, as well as biologic factors, Barrington said.
This study suggests obesity, which is influenced by both social and biologic factors, may play an important role behind what Kristal and Barrington call the “African-American race effect” on disparities in prostate cancer risk.
What drives the disparity? “There is some evidence that the biological responses to obesity, such as inflammation and glucose tolerance, are more pronounced in African-American men; both inflammation and insulin may promote cancer development,” Kristal said.
Obesity May Impact Genes
Obesity might also have an impact on genes that control prostate cancer growth, “but frankly this is just speculation,” he said. “This is the next question for researchers to ask, because the answer will likely tell something very important about prostate cancer development and prevention.”
More than a third of the U.S. population is classified as obese, and the prevalence of obesity among African-American men is slightly higher – 37 percent – compared to 32 percent in non-Hispanic white men, Barrington said.
“Given that obesity is more common among African-Americans, [the prostate cancer-obesity connection] is an important question to study, as it may shed light on how to reduce black/white disparities in prostate cancer incidence,” she said.
While the study’s findings concerning obesity and prostate cancer risk in black men are novel and need to be replicated, they underline the ongoing public health toll of the obesity epidemic.
“Obesity prevention and treatment should be a priority for all Americans, but in particular for African-American men,” Barrington said. “Prostate cancer kills 45 out of 100,000 African-Americans and only 19 out of 100,000 white men, and obesity is contributing to this important health disparity. Health care providers need to consider obesity prevention for their African-American male patients as a targeted strategy to reduce prostate cancer disparities.
Wendy Barrington, Ph.D., M.P.H., is an affiliate public health investigator at Fred Hutchinson Cancer Research Center and an assistant professor at the University of Washington School of Nursing.
Alan Kristal, Dr.P.H., is a member of the Public Health Sciences Division at Fred Hutchinson Cancer Research Center.
”Difference in Association of Obesity With Prostate Cancer Risk Between US African American and Non-Hispanic White Men in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) JAMA Oncol. April 16, 2015
Fred Hutchinson Cancer Research Center is an independent, nonprofit research institute based in Seattle, Fred Hutch houses the nation’s first and largest cancer prevention research program, as well as the clinical coordinating center of the Women’s Health Initiative and the international headquarters of the HIV Vaccine Trials Network. For more information visit www.fredhutch.org or follow Fred Hutch on Facebook, Twitter or YouTube.
The National Cancer Institute and the National Center for Complementary and Alternative Medicine, both of the National Institutes of Health, funded the research.