By Andrew M. Seaman
(Reuters Health) - Obesity may be partly responsible for higher rates of prostate cancer observed among African American men, suggests a new U.S. study.
The links between obesity and prostate cancer among different races is complex, researchers say, but if emphasis is put on keeping people at a healthy weight, the excess burden of this cancer among African Americans might be reduced.
“Targeting obesity prevention among African American men may contribute to reducing prostate cancer disparities,” said Wendy Barrington, the study lead researcher from the University of Washington School of Nursing and the Fred Hutchinson Cancer Research Center in Seattle.
Barrington and her colleagues write in JAMA Oncology that African American men are known to have the highest rate of new prostate cancer cases in the U.S. They also have the highest proportion of aggressive prostate cancers.
Overall, there were an estimated 233,000 new cases of prostate cancer diagnosed in the U.S. during 2014, according to the National Cancer Institute. There were also an estimated 29,480 deaths from prostate cancer that year.
There is no evidence that prostate cancer risk factors like age, smoking status or family medical history affect white and African American men differently. But obesity is also considered a risk factor, and it’s unknown whether that varies between races, the researchers write.
For the new study, they used data from a previous trial that followed the health of 3,398 African American and 22,673 non-Hispanic white men from 2001 to 2011. All were 55 years or older.
After about six years, the researchers found 270 prostate cancer cases among the African American men and 1,453 among white men. Overall, the study team calculates, the African American men had a 58 percent increased risk for prostate cancer compared to white men.
When the researchers considered the participants’ body mass index (BMI), a measure of weight relative to height, obesity was tied to additional prostate cancer risk among African Americans, but not among white men.
African American men of normal weight had 28 percent higher risk of developing prostate cancer compared to white men. But for obese African American men, that risk was 103 percent higher.
The relationship between obesity, prostate cancer and race also differs depending on the aggressiveness of the disease, researchers found.
For example, obesity is tied to an increased risk of aggressive prostate cancer in both African American and white men. But for less-aggressive cancers, obesity is linked to higher risk only for African American men.
The researchers can’t explain why African American men’s risk may be influenced more by obesity than it is for white men. The next step is to look to see if biological differences between the two groups play a role, Barrington said.
“We really don’t know,” she said, adding that the study results also cannot prove that losing weight changes a person’s risk of prostate cancer.
Even with those limitations and the inability of the study to find a reason for the increased risk among African Americans, Dr. Charles Thomas Jr. wrote in an accompanying editorial that the findings “provide a further rationale for weight reduction and a target BMI for clinicians to aim for in care of African American men.”
Thomas, who is a deputy editor of the journal, is a cancer specialist at Oregon Health and Science University in Portland.
“It’s a nice message for the public, because obesity is at the root of so many health problems,” said Dr. Stacy Loeb, a urologist at NYU Langone Medical Center in New York City. “There have been several studies suggesting obesity is a risk factor for prostate cancer particularly for African American men.”
“This could be one of the factors that are involved,” said Loeb, who wasn’t involved with the new study. “I don’t think it definitely answers the questions but it provides another piece of the puzzle.”