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Lead study author and research fellow with the Cancer Epidemiology division of the NCI, Margaret E. Wright, pointed out that the study did not find a link between excess weight and actually contracting prostate cancer.
The NCI researchers began their study in 1995, analyzing health questionnaires filled out by nearly 288,000 men who were between the ages of 50 and 71 at the time. The questionnaire was used to establish the frequency with which participants were tested for prostate cancer though the prostate-specific antigen test and digital rectal exams from 1992 to 1994, and to record weight, height, and body mass index (BMI); a weight classification ratio calculated from both height and weight. At the beginning of the study, 29 percent of the men were considered normal weight, 50 percent were considered overweight, and 21 percent were classified as obese.
All participants were also part of a larger diet and health study conducted by the AARP. None of the men who fell into the smaller BMI sample had ever been diagnosed with any cancer except non-melanoma skin cancer.
Between 1995 and the end of 2000, almost 10,000 participants had contracted prostate cancer, and 173 men had succumbed to the disease, the study authors said. The risk of death, they noted, appeared to be linked to BMI. Overweight men had a 25 percent greater risk of death from prostate cancer than men at normal weight, and mildly obese men -- defined as a BMI between 30 and 34.9 -- were at a 46 percent higher risk. Men who had a BMI of 35 or more were considered severely obese and were at double the normal risk of fatality from prostate cancer.
The study also found that the risk of death from prostate cancer increased in relation to the amount of weight a male gained after turning 18.
"This is a large study, and this finding really solidifies prior indications suggesting this association is real," Wright said. "So while we still need to do more research to find out exactly how this works, I'm not surprised with the connection."
"This adds to observations in a number of different studies that indicate that patients who are in better condition -- thinner, more active, or with a lower BMI -- may have a less aggressive form of cancer and do better than patients who have a sedentary lifestyle," said Dr. Philip Arlen, director of the Clinical Research Group in the Laboratory of Tumor Immunology and Biology with the Center for Cancer Research at the National Cancer Institute. "There are a lot of factors that may come into play, and BMI may not be predictive in terms of developing prostate cancer, but it does seem that among patients already diagnosed, those who are physically active and not obese may face a better outcome," said Arlen, who was not involved in the study.
One in six American men contract prostate cancer, according to the Prostate Cancer foundation, and the disease is the most common form of cancer outside of skin cancers. Age is a common risk factor, and men older than 65 account for more than 65 percent of all prostate cancer cases. Other risk factors include diet and exercise levels, and genetics, although the NCI study found that age, race, frequency of preventative screening, and family history of prostate cancer seemed to have no affect on the link between weight and prostate cancer mortality.
Wright and colleagues noted in their study -- published in the Feb. 15 issue of Cancer -- that almost 66 percent of Americans were fell into the obese or overweight categories as of 2000. In previous studies, excess weight and obesity have been linked to Type 2 diabetes, cardiovascular disease, chronic illness and many cancers besides prostate cancer.
"We have to continue to address the growing prevalence of obesity in this country and others, because obesity is linked to many, many diseases," Wright said. "So we would, of course, definitely recommend that people maintain a healthy weight through diet and exercise."