Obesity Significantly Increases Prostate Cancer Risk in African American Men
Obesity in black men substantially increased the risk of low- and high-grade prostate cancer, whereas obesity in white men moderately reduced the risk of low-grade cancer and only slightly increased the risk of high-grade cancer, according to the first large, prospective study to examine how race and obesity jointly affect prostate cancer risk. The findings, published by Barrington et al in JAMA Oncology, were based on a nationwide study led by researchers at Fred Hutchinson Cancer Research Center and the University of Washington.
The research team, led by senior author Alan Kristal, DrPH, member of the Fred Hutchinson Public Health Sciences Division, and first author Wendy Barrington, PhD, MPH, Affiliate Public Health Investigator at Fred Hutchinson and Assistant Professor at the University of Washington School of Nursing, found that black men who are obese (body mass index [BMI] ≥ 35) had a 122% increased risk of low-grade and an 81% increased risk of high-grade prostate cancer, compared with those who were of normal weight (BMI ≤ 25). In contrast, among non-Hispanic white men, those who were obese had a 20% reduced risk of low-grade and only a 33% increased risk of high-grade prostate cancer, compared with those of normal weight.
“For unknown reasons, African American men have a much higher risk of prostate cancer than non-Hispanic white men. 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,” Dr. Kristal said.
Prostate Cancer–Obesity Connection
According to the National Cancer Institute, black men have the highest prostate cancer rates of any racial or ethnic group in the United States. They tend to get more aggressive forms of this cancer and are more than twice as likely to die of the disease as 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, Dr. Barrington said.
This study suggests obesity, which is influenced by both social and biologic factors, may play an important role behind what Drs. Kristal and Barrington call the “African American race effect” on disparities in prostate cancer risk. More than one-third of the U.S. population is classified as obese, and the prevalence of obesity among African American men is slightly higher—37%—compared with 32% in non-Hispanic white men, Dr. 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.
SELECT Study
The study was based on data collected during the Selenium and Vitamin E Cancer Prevention Trial, known as the SELECT study, an international clinical trial that tested whether supplemental selenium and/or vitamin E could prevent prostate cancer. More than 35,000 men from across the United States, Canada, and Puerto Rico participated. Study participants, including nearly 3,400 African American men, were followed carefully for the development of cancer and other diseases, and a single study pathologist examined prostate tissue from the men diagnosed with prostate cancer to determine whether it was low- or high-grade disease. The trial ended early, because after an average of 5 years, there was no evidence that either of the supplements lowered prostate cancer risk. The study did, however, provide a trove of high-quality data on risk factors such as race, height, weight, and family history, as well as the use of prostate-cancer screening.
The obesity finding was “serendipitous” and “potentially of enormous importance,” Dr. Kristal said. “In an unrelated analysis, we wanted to statistically control for effects of obesity. We noticed that the associations of obesity with prostate cancer risk in African American men were very different than those for non-Hispanic white men.”
Further Research Required
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,” Dr. Kristal said. 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.”
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,” Dr. 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.”
Dr. Barrington is the corresponding author of the JAMA Oncology article.
This study was supported by the National Cancer Institute and the National Center for Complementary and Alternative Medicine, both of the National Institutes of Health.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
