The relationship between obesity and prostate cancer is complex - but the risk is clearly higher in African-Americans, the study finds.
The analysis, published in JAMA Oncology, covers 3,398 African-American and 22,673 non-Hispanic white men who had taken part in the SELECT trial.
They formed a prospective study cohort who had originally been recruited to test whether selenium and vitamin E had a preventive role against prostate cancer - but they gave obesity-related data in the process. Any men who had not yielded data on body mass index (BMI) and other relevant variables were left out of this analysis.
Prostate cancer incidence was the outcome tracked and has been analyzed for its relationship to obesity and race by Wendy Barrington, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, WA.
Dr. Barrington - assistant professor in psychosocial and community health at the University of Washington School of Nursing - accessed data on total numbers of prostate cancer diagnoses, and which of these were low-grade or high-grade.
Grading had been performed in the pathology lab on biopsy samples - to reach a Gleason score, which below 7 means low-grade prostate cancer, or high-grade at 7 and greater.
Key among her findings was that the risk of developing prostate cancer in the African-American men who were obese approached four times the risk of African-American men who had normal weight. Using BMI, the analysis found a:
- 28% risk of getting prostate cancer for the African-American men who had a BMI below 25
- 103% risk for those with a BMI of 35 or more, representing obesity.
By contrast, "obesity was not associated with risk of total prostate cancer" among the non-Hispanic white men in the study, the authors conclude.
Dr. Barrington confirmed the main message of the findings. As corresponding and primary author, she told Medical News Today:
"The main take-home point for practicing physicians is to recognize that obesity has a different relationship to prostate cancer risk in African-American compared to non-Hispanic white men."
Cancer risk from obesity across all men, but especially African-Americans
"Obesity substantially increases the risks of both low- and high-grade prostate cancer among African-American men," Dr. Barrington continued, "but modestly decreases the risk of low-grade, and increases the risk of high-grade, cancer among non-Hispanic white men."
An article linked to the study also picks up on the obesity risk for high-grade prostate cancer. Dr. Charles Thomas Jr, one of the journal's editors and professor in radiation medicine at the Oregon Health & Science University in Portland, writes:
"The risk of developing high-grade disease was associated with higher BMI in all patients, although this risk was higher in African-American men compared with non-Hispanic white men (hazard ratio, 1.81)."
It has not been possible from this study alone to define a clear mechanism behind the association between BMI and risk, the editor's note continues, but the findings "do provide a further rationale for weight reduction and a target BMI for clinicians to aim for in care of African-American men."
Dr. Barrington did cite potential explanations for the particular association between obesity and prostate cancer in African-American men. She told MNT there were "differences in screening, age, education, family history of prostate cancer, history of diabetes, and smoking between African-American and non-Hispanic white men."
As to the practical meaning of the study's findings, Dr. Barrington added:
"Physicians should explain to their African-American patients that obesity is uniquely harmful for them in terms of prostate cancer and recommend appropriate prevention strategies."