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Cancer Risk and the Obesity Epidemic

January 30th, 2008

Overweight and obesity were associated with increased risk for many types of cancer.

The prevalence of obesity is increasing in developed countries. Almost one quarter of women in England are reported to be obese (BMI >30), and about one third are overweight (BMI, 25.0–29.9), whereas in the U.S., one third are obese and almost two thirds are overweight or obese. In the Million Women Study, English and Scottish women (age range, 50–64) self-reported demographic characteristics (BMI, age, geographic region, socioeconomic status, age at first delivery, parity, smoking, alcohol intake, physical activity, menopausal status, and use of hormone therapy) from 1996 through 2001. Investigators analyzed these data in relation to cancer incidence and mortality as reported in the National Health Service central registers.

Increasing BMI was associated with a significant positive trend in relative risk for adenocarcinoma of the esophagus (RR, 2.38); however, risk for squamous carcinoma of the esophagus decreased (RR, 0.26). Melanoma and stomach, colorectal, cervical, bladder, and brain cancers showed no variation in overall risk in relation to BMI. Premenopausal women (but not postmenopausal women who never used HT) had increased risk for colorectal cancer (RR, 1.61) or melanoma (RR, 1.62) with increasing BMI. However, increasing BMI was associated with a decreased risk for breast cancer in premenopausal women (RR, 0.86) and an increased risk in postmenopausal women (RR, 1.36). Endometrial cancer risk increased with BMI in both premenopausal (RR, 1.77) and postmenopausal (RR, 3.98) women. Other cancers for which risk increased with BMI were kidney cancer, leukemia, multiple myeloma, pancreatic cancer, non-Hodgkin lymphoma, and ovarian cancer. Lung cancer incidence decreased with increasing BMI (RR, 0.74); excluding smokers did not substantially alter the results. Overall, for 10 out of 17 specific cancer types examined, increasing BMI was associated with increased incidence and mortality.

Comment: The results of this large prospective study substantiate another potential health risk associated with being overweight or obese: cancer. According to these data, almost half of endometrial cancer and esophageal adenocarcinoma cases can be attributed to being overweight or obese. Menopausal status affects the relation between BMI and cancer risk, not only for hormonally related breast and endometrial cancers but also for colorectal cancer and melanoma. Women at risk for particular cancers because of personal or family history might be especially motivated by these findings to attain or maintain a BMI below 24.9.

Reeves GK et al. Cancer incidence and mortality in relation to body mass index in the Million Women Study: Cohort study. BMJ 2007 Dec 1; 335:1134.

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