Body mass index and risk of colorectal cancer in women (United States).

OBJECTIVE

Epidemiologic data relating obesity to risk of colorectal cancer in women have been inconclusive. Two recent studies have suggested that the association may be modified by estrogen status; BMI was positively associated with colorectal cancer risk among women with high estrogen exposures [premenopausal women, and postmenopausal women who currently received postmenopausal hormone therapy (PMH)]. We prospectively investigated the role of BMI in colorectal cancer risk along with the modifying effects of estrogen in a large cohort from the Women's Health Study.

METHODS

Among 39,876 apparently healthy women aged > or = 45 years at baseline (54% of them were postmenopausal), 37,671 were eligible for the present study. During an average of 8.7 years of follow-up, 202 women had a confirmed diagnosis of colorectal cancer. Baseline BMI was calculated by dividing self-reported weight in kilograms by height in meters squared.

RESULTS

The multivariate relative risks (RRs) and 95% confidence interval (CI) of colorectal cancer were 1.72 (1.12-2.66) for 27-29.9 kg/m2, and 1.67 (1.08-2.59) for > or = 30 kg/m2, as compared with BMI < 23 kg/m2 ( p for trend = 0.02). This positive association was seen primarily in the proximal colon ( p for trend = 0.004). When the association was further examined according to PMH use among postmenopausal women, we found that both current and never users with higher BMI were at a greater risk of colorectal cancer ( p for interaction between BMI and PMH use = 0.33). As compared with BMI < 23 kg/m2, the multivariate RRs and 95% CI for 27-29.9 and > or = 30 kg/m2 were 1.98 (0.98-3.99) and 1.41 (0.65-3.06) among current users, and 1.05 (0.42-2.65) and 2.91 (1.40-6.06) among never users.

CONCLUSIONS

These data suggest that higher BMI was associated with an elevated risk of colorectal cancer, and the positive relationship was not altered by estrogen exposure among postmenopausal women.