WASHINGTON, DC — For the first time, a report from an ongoing systematic review of global research finds that being overweight or obese increases men’s risk for the deadliest forms of prostate cancer.
The report also downgrades the strength of the evidence linking lycopene and selenium to reduced risk for prostate cancer. Another previous judgment, that diets high in calcium were linked to increased prostate cancer risk, has been downgraded to “limited, but suggestive.”
Today, in partnership with the American Institute for Cancer Research (AICR), World Cancer Research Fund (WCRF) International’s Continuous Update Project (CUP) released the report Diet, Nutrition, Physical Activity and Prostate Cancer. The report collectively analyzed 104 studies involving over 9.8 million men and more than 191,000 cases of prostate cancer. It is the most in-depth review to date of global research linking diet, physical activity, and weight to the risk of developing prostate cancer.
Obesity Now A Risk Factor
The independent expert panel that authored today’s report concluded that excess body fat increases the risk for advanced prostate cancers, including aggressive prostate cancers, which are often fatal. In fact, AICR now estimates that 11 percent of all advanced prostate cancer cases in the U.S. could be prevented by being a healthy weight.
“This is the first time our rigorous process has uncovered a clear and consistent link between body fat and prostate cancer,” said CUP Panel lead Edward Giovannucci, M.D., Sc.D. of the Harvard School of Public Health. “Today we have something new to tell men worried about this disease: you can take steps to help protect yourself from its most aggressive and deadliest forms.”
Body fat is metabolically active tissue which secretes compounds into the bloodstream that alter the body’s hormonal environment in ways that are thought to increase risk for many cancers. Prostate cancer today becomes the ninth cancer officially linked to obesity by the experts: previous reports from AICR and WCRF International have also found that excess body fat increases risk for ovarian cancer, post-menopausal breast cancer, colorectal cancer, endometrial cancer, esophageal cancer, kidney cancer, gallbladder cancer and pancreatic cancer.
Giovannucci noted that in the seven years since AICR and WCRF International released their Second Expert Report on cancer prevention, the nature of prostate cancer research has changed. “We now know that not all prostate cancers are the same, and research is only beginning to account for that,” Giovannucci said.
“Widespread PSA screening has led to the diagnosis of many thousands of prostate cancers that will never become life-threatening, for example. Today’s studies are separating out the aggressive, advanced, and fatal forms of the disease. As they do, it’s become clear that obesity is linked to those aggressive, often deadly forms, and not to the latent or indolent forms that rarely become life-threatening.”
Lycopene, Selenium, Calcium: Links Now “Harder to See”
But while knowing more about prostate cancer has made the nature of its link to obesity more clear, it has simultaneously rendered judgments about other dietary links more difficult to make.
In 2007, the AICR/WCRF report concluded that strong evidence linked foods containing lycopene (such as tomatoes and watermelon) to lower risk of prostate cancer. Today’s report downgrades that judgment to a category that states the evidence is too limited to make a conclusion. Similarly, the report also downgraded a judgment on selenium. The previous report found that foods containing selenium (and selenium supplements) were linked to lower risk; the report now finds the evidence is limited, although consistent.
Another previous judgment, that diets high in calcium are linked to increased risk for prostate cancer, also sank into a category of “limited” evidence, meaning it is not strong enough to be incorporated into AICR’s official Recommendations for Cancer Prevention, which will be reviewed in 2017.
“The data on these factors have grown noisy over the past seven years,” said Giovannucci, “too noisy to judge them conclusively. We are not saying that any of these links now don’t exist – it’s just that, if they do, they’ve become much harder to see.”
Every year in the U.S. approximately 233,000 new cases of prostate cancer are diagnosed; of this number more than 16,000 are advanced prostate cancer. It is the 2nd leading cause of cancer death in U.S. men.
Approximately 71 percent of U.S. men are overweight or obese, placing them at increased risk for developing advanced prostate cancer. If you don’t know whether you fall in the range classified as “healthy weight” by researchers you can check your BMI status on the AICR website.
“These latest findings from the Continuous Update Project offer another reminder that our weight plays an important role in cancer risk,” said AICR Associate Director of Nutrition Programs Alice Bender, M.S., R.D.N. “That’s an empowering message. It means that doing what you can to get to and stay at a healthy weight, like adding physical activity to your day and focusing on healthy plant foods on your plate, can offer real, measurable protection against this deadly disease, and a host of other chronic conditions as well.”
In 2007, AICR and WCRF published an Expert Report that weighed the evidence linking various lifestyle factors to 17 different cancers, and released 10 Recommendations for Cancer Prevention.
Since that time, the CUP has continued to monitor and analyze global research and draw conclusions about how diet, weight and physical activity affect the chances of developing various cancers. To date, new CUP Reports have reviewed the updated evidence on the prevention of breast, colorectal, pancreatic, endometrial and ovarian cancers. More reports will be published over the next three years; in 2017, AICR is scheduled to release new, updated Recommendations for Cancer Prevention.