Excess weight, adult weight gain may increase prostate cancer death

Obesity may increase the risk of death from prostate cancer, even though it does not increase the overall risk that a man will be diagnosed with the disease, suggests a study to be published in Cancer.

The study revealed that higher body mass index and weight gain in adulthood correlated strongly with increased risk of death from prostate cancer. However, no such association was found between body mass index or weight gain and the development of the cancer.

Led by Margaret E. Wright, PhD, of the National Cancer Institute in Bethesda, MD, researchers followed 287,760 men, ages 50 to 71 years, as part of the NIH-AARP Diet and Health Study to examine the individual impact of body mass index and adult weight change on the incidence, severity, and outcome of prostate cancer.

They found that higher BMI and weight gain since the age of 18 were associated with significantly higher risk of death from prostate cancer. As BMI increased, so did the relative risk of death. Men who were overweight had a 25% higher risk, mildly obese men had a 46% higher risk, and severely obese men had a 100% risk. Similarly, men who gained weight since the age of 18 were also at increased risk of a fatal outcome. Neither being overweight nor being obese, however, was associated with developing prostate cancer.

A separate study of nearly 70,000 men found that men who lose weight may reduce their risk of prostate cancer (Cancer Epidemiol Biomarkers Prev 2007;16:63-9). The study also found that obesity selectively increases the risk of more aggressive prostate cancer while decreasing either the occurrence or the likelihood of diagnosis of less-aggressive tumors.

Carmen Rodriguez, MD, and colleagues from the American Cancer Society and the Duke Prostate Center, Durham, NC, used data from the Cancer Prevention Study II Nutrition Cohort to examine the association between adult BMI and prostate cancer incidence by stage and grade at diagnosis, as well as the association between weight change and prostate cancer incidence. Men reported their weight in 1982 and again in 1992.

They were followed for 10 years, until June 2003, during which time more than 5,000 cases of prostate cancer occurred among the group.

After adjusting for variables such as age, ethnicity, smoking, diet, PSA screening, and other factors, researchers found that BMI in 1992 was not associated with the overall risk of prostate cancer in the next 10 years. But when they stratified the results by tumor grade, they found the risk of non-metastatic low-grade prostate cancer decreased significantly with increasing BMI. In contrast, the risk of non-metastatic high-grade prostate cancer increased modestly with increasing BMI, and the risk of metastatic cancer increased steadily with increasing BMI.

"Obesity is one of the most prevalent modifiable cancer risk factors," Dr. Rodriguez said. "Although our study suggests that weight loss may lower the risk of aggressive prostate cancer, given the difficulty of losing weight, emphasis should be put on the importance of avoiding weight gain to reduce the risk of prostate cancer."