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Greater BMI in women linked to higher risk for several cancers, large investigation shows

Tuesday, January 08 2008 | Comments

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What's This? Results from the Million Women Study demonstrate that the risks of several types of cancers significantly increase as body mass index rises.

For this analysis, researchers evaluated the incidence of cancer and related mortality in approximately 1.2 million women aged 50 to 64 years at the start of the Million Women Study. Participants provided information about height and weight and did not have cancer at baseline (except possibly nonmelanoma skin cancer). Researchers evaluated the overall incidence of cancer in the cohort as well as the incidence of 17 specific types of cancer and cancer-related mortality rates.

Overall, 45,037 incident cancers and 17,203 cancer deaths occurred during 5.4 years and 7.0 years of follow-up, respectively.

In adjusted analyses, each 10-unit increase in BMI was associated with a 12% increase in the risk of any cancer (95% CI, 1.09-1.14).

A 10-unit increase in BMI was also associated with a significantly increased risk of endometrial cancer (RR, 2.89), esophageal adenocarcinoma (RR, 2.38), kidney cancer (RR, 1.53), leukemia (RR, 1.50), pancreatic cancer (RR, 1.24), non-Hodgkin's lymphoma (RR, 1.17), ovarian cancer (RR, 1.14), and multiple myeloma (RR, 1.31).

However, the same increase in BMI was associated with a decreased risk of squamous cell carcinoma (RR, 0.26; 95% CI, 0.18-0.38) and a reduced risk of lung cancer (RR, 0.74; 95% CI, 0.67-0.82).

Patterns of cancer mortality with increasing BMI were generally similar to the patterns observed for cancer incidence, the authors noted.

They added that the risk of breast cancer, endometrial cancer, colorectal cancer, and malignant melanoma varied significantly by menopausal status.

Among women who had never used hormone replacement therapy, the risks of colorectal cancer and malignant melanoma increased with BMI in premenopausal women (RR, 1.61 and 1.62, respectively, per 10-unit increase in BMI), but not in postmenopausal women. In contrast, the risk of breast cancer increased with increasing BMI in postmenopausal women (RR, 1.40), but a higher BMI was actually  associated with a reduced risk of breast cancer in premenopausal women (RR, 0.86). The risk of endometrial cancer increased with increasing BMI in both subgroups, but the risk increased much more dramatically in postmenopausal women (RR, 3.98 vs 1.77).

The researchers estimated that 5% of all cancers in postmenopausal women could be attributed to overweight or obesity, including approximately half of the cases of endometrial cancer and adenocarcinoma of the esophagus.

"Thus, in total, we found a significant increase in risk with increasing BMI in 10 out of the 17 specific types of cancer considered, including 8 sites in which a positive association existed in all women and 2 sites in which it was confined to either premenopausal women (colorectal cancer) or postmenopausal women (breast cancer)," the study authors summarized. (Reeves GK, et al. BMJ 2007; 335:1134-1144.)

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