Obesity and lack of exercise contribute to up to a third of cancers of the colon, breast, kidney, and digestive tract, says a new report from the World Health Organization. The study was prompted by concerns that obesity and its attendant health risks constitute a growing global epidemic.
The Centers for Disease Control and Prevention (CDC) estimate that obesity causes 300000 deaths in the United States annually, a number exceeded only by deaths related to tobacco. Half of European adults and 61% of Americans are overweight. Moreover, the proliferation of Western diets and sedentary lifestyles in developing countries poses a threat to people who were previously at low risk of obesity.
Obesity consumes 8% of the US healthcare budget and an estimated $100bn (£71.4bn) in direct and indirect costs. It is well known that obesity increases the risk of cardiovascular diseases, but its role in oncogenesis is less understood. Several studies have shown that obesity increases the risk for cancers of the colon, breast, endometrium, kidney, and oesophagus (adenocarcinoma).
The mechanism of increased cancer risk in obese populations is unclear, but nutritional and dietary factors may have a role. Changes in metabolism and hormonal activity may also be implicated, particularly in hormone responsive cancers such as breast, prostate, and endometrial carcinomas. Oestrogens serve as growth factors for both breast and endometrial cancers and fat cells serve as a source for androstenedione, which is converted into estrogens.
Evidence exists that weight gain increases cancer risk, but the converse proposition—that weight loss would reduce risk of the disease—has not been confirmed. The WHO panel said that despite the lack of direct evidence, hormonal changes produced by weight loss seem likely to reduce risks of some cancers, especially breast and uterine cancer.
The researchers urged a multipronged approach to combat the obesity epidemic, involving federal and local governments, educational systems, families, and individuals. Governments and schools should be encouraged to fund programs to promote physical activity, and urban planning should be designed to be conducive to a healthy lifestyle. “‘Obesity cannot be prevented or managed, nor physical activity promoted, solely at the level of the individual governments, the food industry, international agencies, the media, communities, and individuals all need to work together to modify the environment so that it is less conducive to weight gain,” the WHO panel concluded.
The WHO report is at www.iarc.fr/pageroot/UNITS/Chemoprevention2.html
Figure.
DAVID BLATTEL/THE STOCK MARKET
Inactivity and Western diets can cause many common cancers