NEW YORK (Reuters Health) - A high body mass index (BMI) does not increase the risk of developing prostate cancer, but once the disease occurs, a high BMI is associated with a greater risk of dying from the cancer, researchers report.

"This is a large study that shows a convincing dose-response association between obesity and adult weight gain and death from prostate cancer," lead investigator Dr. Margaret E. Wright told Reuters Health.

Wright, at the National Cancer Institute, Bethesda, Maryland, and colleagues studied data on 287,760 men taking part in a diet and health study. After 5 years of follow-up, there were 9986 new cases of prostate cancer, and after 6 years of follow-up, there were 173 deaths from prostate cancer, the researchers report in the medical journal Cancer.

A BMI up to 25 is considered normal weight, up to 30 is classified as overweight, and 30 and up indicates obesity.

In this study, a higher BMI at the outset was associated with significantly reduced likelihood of developing prostate cancer. Men with a BMI of 40 or more had a 33 percent lower risk of prostate cancer than men with a BMI of less than 25.

Conversely, the risk of dying of prostate cancer rose significantly with increasing BMI. This amounted to a 25 percent greater risk for men with a BMI between 25 and 29.9, a 46 percent increase for BMIs between 30 and 34.9, and more than double the risk if BMI was 35 or more.

There was also a significant association between weight gain in adulthood and prostate cancer mortality.

"The growing prevalence of obesity in Western countries is alarming," Wright said, "and reducing the risk of prostate cancer death is only one among many health reasons to maintain a healthy weight through diet and exercise."