Obesity is a risk factor for more cancers than previously believed, according to the results of a new evaluation conducted by the IARC Handbooks of Cancer Prevention program under the World Health Organization.
The conclusions were based on the results of a systematic review of more than 1,000 studies by the Working Group for IARC Handbooks For Cancer Prevention Volume 16: Body Fatness, who also came to the conclusion that the absence of excess body fat is cancer-preventive.
Results were recently published in the New England Journal of Medicine under the title “Body Fatness and Cancer — Viewpoint of the IARC Working Group.”
The group of 21 international experts studied data on more than 20 cancer types and the impact of overweight bodies or obesity at different ages on cancer risk. They concentrated on interventional trials, cohort and case-control studies, experimental animal studies, and research studies that linked excess body fat to cancer.
Also reviewed was data on the impact on cancer risk after a change in weight during adulthood or during early life. Available data regarding the effect of obesity and of weight loss in cancer patients in terms of cancer recurrence or cancer-related survival, was also considered.
“This comprehensive evaluation reinforces the benefits of maintaining a healthy body weight in order to reduce the risk of several different types of cancer,” said Dr. Béatrice Lauby-Secretan, lead author of the study, in a press release.
The report shows that the absence of excess body fatness reduces the risk of cancers of the colon and rectum, pancreas, thyroid, gallbladder, oesophagus, gastric cardia, liver, kidney, ovary, endometrium of the uterus, breast in postmenopausal women, meningioma and multiple myeloma.
In addition, the absence of excess body fatness may reduce the risk of fatal cancer of the prostate, diffuse large B-cell lymphoma, and breast cancer in men.
The group also examined studies about body fatness in children and young people to evaluate if obesity is associated with development of cancer later as adults. For some sites such as the liver and colon, the group found comparable links to cancer found in adults.
Evidence from animals studies showed that overweightness is associated with an increase in the incidence of several types of cancer in animals while caloric or dietary restriction is associated with decreases in the risk of mammary gland, liver, colon, skin, pancreas and pituitary gland cancers.
Body fatness is usually measured by body mass index (BMI). Estimates from 2014 indicated that 640 million adults worldwide were obese, six times more than estimated in 1975. In 2013, an estimated 110 million children and young people were obese — twice as many from 1980. Globally, there are more people obese or overweight than there are people who are underweight.
Estimates show that in 2013, 4.5 million deaths worldwide were associated with obesity or overweight bodies. The recognition of new cancer sites related to obesity are expected to add to the number of deaths related to obesity.
“The new evidence emphasises how important it is to find effective ways, at both the individual and societal level, to implement World Health Organization recommendations on improving diets and physical activity patterns throughout life if the burden of cancer and other noncommunicable diseases is to be tackled,” said IARC Director, Dr. Christopher Wild.
Annie Anderson, professor of public health nutrition at the University of Dundee, concluded, “This report reaffirms the importance of trying to maintain an appropriate body weight to decrease the risk of a range of cancers.”