The WHO’s International Agency for Research on Cancer working group identified an additional eight types of cancer associated with excess body fatness, including multiple myeloma; meningioma; and cancers of the gastric cardia, liver, gallbladder, pancreas, ovary and thyroid.
These tumor sites are in addition to the cancers identified in 2002 by the same group to be associated with body fatness. The originally identified cancers included cancers of the colon, esophagus, kidney, breast and uterus.
“The burden of cancer due to being overweight or obese is more extensive than what has been assumed,” Graham Colditz, MD, DrPH, deputy director of the Institute for Public Health at Washington University in St. Louis and chair of the International Agency for Research on Cancer working group, said in a press release. “Many of the newly identified cancers linked to excess weight haven't been on people's radar screens as having a weight component.”
An estimated 640 million adults worldwide were obese — defined as a BMI of 30 or higher — in 2014, and an estimated 110 million children and adolescents were obese in 2013, representing an increase of a factor of 2 since 1980.
Further, an estimated 4.5 million deaths worldwide were caused by overweight and obesity in 2013. Obesity-related cancers represent up to 9% of cancers in North America, Europe and the Middle East.
“Significant numbers of the United States and the world's population are overweight,” Colditz said. “This is another wake-up call. It's time to take our health and our diets seriously.”
Colditz and colleagues of the International Agency for Research on Cancer working group reviewed more than 1,000 epidemiologic studies, most of which were observational studies on cancer risk and excess body fatness.
A review of the data from these studies reaffirmed that the absence of excess body fatness reduced the risk for cancers in the organ sites identified in 2002.
Researchers also identified eight additional cancers with sufficient evidence linking them to excess body fatness, with RRs calculated in comparison of the highest BMI category vs. normal BMI:
- gastric cardia cancer (RR = 1.8; 95% CI, 1.3-2.5);
- liver cancer (RR = 1.8; 95% CI, 1.6-2.1);
- gallbladder cancer (RR = 1.3; 95% CI, 1.2-1.4);
pancreatic cancer (RR = 1.5; 95% CI, 1.2-1.8);
- ovarian cancer (RR = 1.1; 95% CI, 1.1-1.2);
- meningioma (RR = 1.5; 95% CI, 1.3-1.8);
- thyroid cancer (RR per 5 BMI units = 1.1; 95% CI, 1-1.1); and
- multiple myeloma (RR = 1.5; 95% CI, 1.2-2).
The risk for these cancers associated with excess body fatness occurred in a dose–response relationship, where higher BMIs led to greater risk.
Eight additional cancer types — including cancers of the lung, esophagus, gastric noncardia, extrahepatic biliary tract, skin, testis, urinary bladder, and brain or spinal cord — had an inadequate association with excess body fatness due to limited data, inconsistent results or no data suggesting an association.
Data on BMI in children and adolescents revealed similar trends related to excess body fatness in all cancer types with the exception of postmenopausal breast cancer.
Researchers noted there was considerable variation in study design, setting and timing of body-fatness measurements in studies evaluating the association between weight and cancer recurrence and survival after diagnosis. Still, they identified a large volume of evidence to support the association between increased BMI near the time of cancer diagnosis and reduce breast cancer survival.
An evaluation of experimental animal studies and mechanistic data suggested a causal cancer-preventative effect of intentional weight loss; however, the researchers noted this association lacks data in humans.
“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,” Colditz said. “Public health efforts to combat cancer should focus on these things that people have some control over. But 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.” – by Alexandra Todak
Disclosure: One researcher reports grant support from the CDC and American Cancer Society outside the submitted work.