New evidence published today by the World Health Organization's International Agency for Cancer on Research (IARC) provides even more of a reason to maintain a healthy weight as we age. The international team of researchers has identified eight additional types of cancer linked to excess weight and obesity: stomach, liver, gallbladder, pancreas, ovary, meningioma (a type of brain tumor), thyroid cancer, and the blood cancer multiple myeloma.
In 2002 the same group produced substantial evidence that linked five other cancers to being overweight or obese: adenocarcinoma of the esophagus, kidney cancer, colorectal cancer, breast cancer in postmenopausal women, and uterine cancer. This new study reinforces the notion that limiting weight gain over the decades could help to reduce the risk of all 13 cancer types.
The findings from this study were published today in The New England Journal of Medicine in an article entitled “Body Fatness and Cancer—Viewpoint of the IARC Working Group” and are based on a review of more than 1000 studies of excess weight and cancer risk.
“The burden of cancer due to being overweight or obese is more extensive than what has been assumed,” explained Graham Colditz, M.D., Dr.P.H., a cancer prevention expert at Washington University School of Medicine in St. Louis, who chaired the IARC Working Group. “Many of the newly identified cancers linked to excess weight haven't been on people's radar screens as having a weight component.”
The IARC team believes that their new findings could have a significant bearing on the global population. Worldwide, an estimated 640 million adults and 110 million children are obese, including one-third of adults and children in the United States.
“Lifestyle factors such as eating a healthy diet, maintaining a healthy weight, and exercising, in addition to not smoking, can have a significant impact on reducing cancer risk,” Dr. Colditz noted. “Public health efforts to combat cancer should focus on these things that people have some control over.”
However, Dr. Colditz added that “losing weight is hard for many people. Rather than getting discouraged and giving up, those struggling to take off weight could instead focus on avoiding more weight gain.”
Interestingly, the investigators found that for most of the cancers on the newly expanded list, a positive dose–response relationship exists, i.e., the higher the body mass index, or BMI, the greater the cancer risk. Moreover, the cancer risks associated with excess weight were similar for men and women and, when data were available, were consistent across geographic regions—North America, Europe, Asia, and the Middle East.
In addition to providing data linking the excess weight to the additional cancer types, the researchers also looked to provide mechanisms as to why being overweight or obese can increase an individual’s cancer risk. While there are numerous possible explanations, the scientists specifically noted that excess fat leads to an overproduction of estrogen, testosterone, and insulin and also promotes inflammation, all of which can drive cancer growth.
“Significant numbers of the U.S. and the world's population are overweight,” Dr. Colditz concluded. “This is another wake-up call. It's time to take our health and our diets seriously.”