TUESDAY, Sept. 1, 2009 (HealthDay News) -- Men who pack on excess pounds as young adults are at heightened risk of developing prostate cancer, although the risk varies by ethnic group, researchers from the University of Hawaii report.
Obesity is a risk factor for many common cancers, including colorectal cancer and breast cancer in postmenopausal women. However, whether obesity plays a role in prostate cancer risk has been unclear, researchers say.
The new study finds that "body mass in both younger and older adulthood, and weight gain between these periods of life, may influence prostate cancer risk," said study author Brenda Y. Hernandez, an assistant professor at the Cancer Research Center of Hawaii.
The report is published in the September online issue of Cancer Epidemiology, Biomarkers & Prevention.
For the study, Hernandez's team looked at the relationship between weight and prostate cancer in a multiethnic population including blacks, Japanese, Hispanics, Native Hawaiians and whites, all of whom who participated in a long-term study called the Multiethnic Cohort.
The researchers collected data on almost 84,000 men who participated in the study. In all, more than 5,500 men were diagnosed with prostate cancer. Men who were overweight or obese at 21 had a lower risk of localized and low-grade prostate cancer, the researchers found.
When men put on weight seemed to matter, as did race and ethnicity. For example, "higher weight in older adulthood was associated with increased risk of prostate cancer among white and Native Hawaiian men and a decreased risk of prostate cancer among Japanese men," Hernandez said.
And excessive weight gain in young adulthood increased the risk of advanced and high-grade prostate cancers (the more dangerous kind) for white men, the report found. For black men, excessive weight gain as a young adult upped risks for less hazardous, localized and low-grade forms of the disease.
Genes and lifestyle may account for these differences in risk, Hernandez speculated. "The relationship of certain characteristics, such as body size, with cancer risk may vary across ethnic groups due to the combined influence of both genes and lifestyle," she said. "This study underscores the importance of investigating cancer etiology in diverse populations."
Victoria Stevens, strategic director of laboratory services at the American Cancer Society, said the study shows there are differences in ethnic groups, but these differences are not straightfoward.
"Their findings aren't definitive," Stevens said. "They are just not clear-cut, you don't see a simple linear relationship."
"The paper is very suggestive, but it is not clear in prostate cancer whether weight gain is as important" as it is for other malignancies, she said. "Exactly what that risk is, we still don't know."
For more information on prostate cancer, visit the American Cancer Society.