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NEWS & VIEWS |
Being overweight or obese substantially increases the risk of dying from cancer, according to researchers from the ACS.
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In a new study published in the New England Journal of Medicine (2003;348:1625–1638), Eugenia Calle, PhD, and colleagues determined that overweight and obesity may account for 20% of all cancer deaths in US women and 14% in US men. That means 90,000 cancer deaths could be prevented each year if Americans could only maintain a healthy body weight.
"As a society, we have not really acknowledged the contribution of obesity to chronic disease in general and cancer in particular," said Calle, Director of Analytic Epidemiology at the ACS. "We are not taking it seriously enough to turn it around."
The researchers followed more than 900,000 men and women in the society’s Cancer Prevention Study II cohort for 16 years to determine the role of body mass index, or BMI (weight in kilograms divided by the square of height in meters) in cancer deaths. People with a BMI between 25 and 29.9 are considered overweight; those with a BMI of 30 or more are considered obese. People with a BMI between 18.5 and 24.9 are considered of normal weight. In the year 2000, about 65% of US adults were overweight or obese, according to the Centers for Disease Control and Prevention, and about 31% were obese.
Calle and her colleagues found that the heaviest men in the study had death rates from all cancers combined that were 52% higher than the rates among normal-weight men. The heaviest women had cancer death rates 62% higher than normal-weight women. Their work substantiated previous studies that linked excess weight and obesity to cancers of the uterus, kidney, esophagus, gallbladder, colon and rectum, and breast (in postmenopausal women).
The effects on breast cancer are compounded, Calle said, because obesity increases a woman’s risk of developing the disease in the first place and her risk of dying from it once she has it. This study also found that many types of cancer not previously linked to obesity were, in fact, affected by excess body weight. Those included cancers of the liver, pancreas, prostate, cervix, ovary, and stomach (in men), as well as non-Hodgkin lymphoma and multiple myeloma.
"Overweight and obesity has a very broad impact on cancer across most cancer sites," Calle said. "That’s not something that’s really in the consciousness of the American people." In fact, in an ACS survey conducted in 2002, just 1% of Americans identified maintaining a healthy weight as a way to reduce cancer risk.
Obesity is thought to influence cancer risk by raising levels of steroid hormones like estrogen and peptide hormones like insulin and insulin-related growth factors. Losing weight has been shown to improve insulin sensitivity and to decrease the level of sex hormones in the blood, Calle said, so "it is reasonable to assume" that losing weight will also decrease cancer risk. However, she noted, too few people have been able to maintain a significant weight loss for that theory to be studied directly.
In addition to these endocrine mechanisms, obesity can cause acid reflux, an important risk factor for esophageal adenocarcinoma. Excess weight is also associated with gallstone formation, which increases the risk of gallbladder cancer.
But Calle acknowledges that losing weight and keeping it off are increasingly difficult challenges. "We live in a society where people have to work very hard to eat right and get physical activity," she said. "People work long hours that leave little time for exercise or cooking healthy meals; Americans must rely heavily on cars to get around; sedentary activities like watching television or using the computer have become more common."
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