How Weight Affects Cancer

The connection between obesity and cancer was researched for 29 years in Sweden. The study that resulted from the research, published in the January 2001 issue of Cancer Causes and Control, evaluated the relationship between obesity and cancer risk. More than 28,000 Swedish patients who were diagnosed as obese were followed for up to 29 years. The researchers compared the incidence of cancer in these patients with the incidence in the general Swedish population.

They found 33 percent more cases of cancer among the obese people than in the general population (25 percent more among men and 37 percent more among women). The obese patients had an increased risk for Hodgkin’s disease (among men) and cancers of the endometrium, kidney, gallbladder, colon, pancreas, bladder, cervix, ovary, and brain. An association between obesity and liver cancer was also found, but that may be explained by the presence of diabetes and alcoholism in these patients. The researchers also found some associations between obesity and cancer that were not found by previous researchers, including non-Hodgkin’s lymphoma (among women) and cancers of the small intestine and larynx. They recommended further study of the association between obesity and these types of cancer.

In another study, published in the November 2, 2000, issue of The New England Journal of Medicine , researchers examined the health records of 363,992 Swedish men who had at least one physical exam between 1971 and 1992, and were followed until their death or the end of 1995. Compared with men in the lowest range for BMI, men in the middle range had a 30- to 60-percent greater risk of renal cell cancer (the most common type of kidney cancer), and men in the highest range had nearly double the risk. There was also a direct association between higher blood pressure and a higher risk of renal cell cancer. A reduction in blood pressure appeared to lower the risk of renal cell cancer.

Obesity may also play a role in a type of esophageal cancer called adenocarcinoma. A study sponsored by the National Cancer Institute concluded that excess abdominal fat may lead to reflux disease (a condition in which liquid from the stomach backs up into the esophagus) by increasing pressure on the stomach. Reflux disease can cause inflammation of tissues at the bottom of the esophagus and can lead to a precancerous condition called Barrett’s esophagus, which may develop into cancer of the esophagus. The researchers noted that, although obesity may contribute to reflux disease, it is unclear exactly how obesity increases the risk of esophageal cancer. The research team is also studying dietary factors, but analyses have not been completed.

Research needs

More research is needed to better understand the effect of obesity on the development of cancer. In particular, studies are needed to evaluate the combined effects of diet, body weight, and physical activity. For some types of cancer, such as colon and breast, it is not clear whether the increased cancer risk is due to extra weight, inadequate consumption of fruits and vegetables, or a high-fat, high-calorie diet. Lack of physical activity also contributes to obesity and appears to be associated with increased risk of cancers of the breast and colon. Physical inactivity may also be associated with other types of cancer, such as prostate cancer.

However, because physical activity level is difficult to measure, its impact on cancer may be underestimated due to misclassification. In the future, researchers may measure physical fitness, rather than level of physical activity. Physical fitness appears to predict heart disease better than measures of physical activity; the same may be true for cancer. The complex relationship between physical activity and obesity makes it important that researchers include both factors in future epidemiological investigations.

IARC recommendations

In February 2001, a panel of experts met at the International Agency for Research on Cancer (IARC) in Lyon, France, and concluded that overweight and a sedentary lifestyle are associated with several diseases, including cancer. The panel recommended that prevention of obesity begin early in life, based on healthy eating habits and regular physical activity. The panel advised people who are overweight or obese to avoid gaining additional weight, and to lose weight through dietary changes and exercise. The IARC, which is part of the World Health Organization, coordinates and conducts research on the causes of cancer and develops scientific strategies for cancer control.

Resources

The following U.S. Government agencies have information about controlling weight and preventing overweight and obesity:

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Weight-control Information Network (WIN)

Address: One Win Way, Bethesda, MD 20892–3665

Telephone: 202–828–1025 or 1–877–946–4627

Fax: 202–828–1028

Internet Web site:http://win.niddk.nih.gov/index.htm

WIN is a national public information service of the NIDDK. WIN assembles and distributes information and publications about weight control, obesity, and nutritional disorders.

National Heart, Lung, and Blood Institute (NHLBI)

Obesity Education Initiative

Address: Post Office Box 30105, Bethesda, MD 20824–0105

Telephone: 301–592–8573

Fax: 301–592–8563

Internet Web site: http://www.nhlbi.nih.gov

The NHLBI’s Obesity Education Initiative seeks to reduce the risk of heart disease and overall morbidity and mortality from heart disease by reducing the prevalence of overweight and physical inactivity. The NHLBI Web site has information for health professionals as well as patients and the general public.