According to the findings from a randomized, controlled clinical trial, obesity is associated with an 80 percent increase in the risk of high-grade, aggressive prostate cancer.

The researchers also found that "apple-shaped" men, who stored fat in the abdominal area, and who had a first-degree relative with prostate cancer, had the greatest risk of both low- and high-grade prostate cancer.

The study also found an increased risk of low-grade prostate cancer among the tallest men in the study, a finding that confirms previous research. "The correlation between height and prostate cancer probably has to do with the role of steroid hormones such as testosterone and estrogen that regulate both prostate development and height," study author Alan Kristal said.

Interestingly, the study also found that obesity is linked to an 18 percent reduced risk of low-grade, non-aggressive prostate cancer, which accounts for about 80 percent of all cases. "This difference in the effect of obesity on low- and high-grade cancer answers a perplexing enigma about prostate cancer," Kristal said. "It helps explain why obese men are more likely to die of prostate cancer, as they are much more likely to get the form of prostate cancer that is difficult to treat and is often fatal."

The mechanisms behind the link between obesity and the most aggressive, fatal form of prostate cancer are believed to involve both steroid hormones and systemic inflammation. "Obesity is a massive inflammatory condition," Kristal said. "It also increases levels of circulating estrogens and growth factors that promote cell growth."

While previous studies have examined the link between obesity and prostate cancer risk, the results have been inconsistent. This is the largest and most comprehensive analysis to date regarding the impact of obesity on prostate cancer risk. The study involved more than 10,000 participants, approximately one-fifth of whom developed prostate cancer.

Strengths of the study include the fact that all of the men were screened for prostate cancer based on PSA level, digital-rectal exam and biopsy. In addition, all of the tissue analysis was done by a central pathology laboratory, ensuring consistent interpretation of cancer grade. Measurements such as height and weight also were collected by trained staff as opposed to relying on participants' self-report.
References:
1. Alan Kristal, et al. Fred Hutchinson Cancer Research Center.