Body Mass Index and Risk of Colorectal Cancer in Women (United States)

Abstract

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 ≥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 ≥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 2, the multivariate RRs and 95% CI for 27–29.9 and ≥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.