Introduction: Overweight and obesity are independent risk factors for colorectal cancer among men and women. Associations of body mass index (BMI) with colorectal cancer risk are stronger among men than women. Evidence on the association of anthropometric factors with colorectal adenoma is more equivocal, especially among women. It has been suggested that the association of BMI with adenomas is weaker among postmenopausal women as compared to premenopausal women but data on this finding is limited. A recent study among participants in the PLCO trial failed to show an association of BMI with either colorectal adenoma or colorectal cancer risk among men and women. However, it is possible that BMI might not be the most relevant marker of obesity-associated colorectal neoplasia risk among women. A large cohort study of European Caucasian women showed a higher risk of colorectal cancer with waist circumference but not BMI. There are relatively few studies that have investigated multiple measures of obesity as risk factors for colorectal adenoma and cancer among women and none have been adequately powered for these analyses among African American women. We investigated the association of BMI and waist circumference as risk factors for colorectal adenoma among postmenopausal African American women in the Black Women's Health Study.

Methods: We conducted a nested case-control study among participants in the Black Women's Health Study - a cohort study of 59,000 women followed biennially since 1995. Cases were defined as women diagnosed with incident colorectal adenoma between 1997 and 2011. Only those adenoma cases verified by medical record review were included. Controls were participants who also underwent lower gastrointestinal endoscopy and in whom no adenoma or other polyp was found. 3 controls were matched to each case based on age and follow-up period. Weight, height, and abdominal circumference were self-reported by participants at baseline. Weight and waist circumference were updated based on self-report every two years. BMI was categorized into 3 categories: 18-24.9 kg/m2 (normal BMI), 25-29.9 kg/ m2 (overweight), and ≥30 kg/ m2 (obese). Waist circumference was categorized in quintiles based on the distribution among controls. Using logistic regression models, we obtained odds ratios (OR) for colorectal adenoma in relation to BMI and waist circumference, adjusting for age, education, physical activity, fruit and vegetable intake, family history of colorectal cancer, smoking, alcohol intake, energy intake, aspirin use, menopausal status, and post-menopausal hormone therapy.

Results: There were 915 adenoma cases and 2,745 controls. After adjusting for multiple covariates, neither overweight (OR: 1.10, 95% CI: 0.88-1.38) nor obese (OR: 1.09, 95% CI: 0.85-1.41) African-American women were at increased risk of colorectal adenomas than women with normal BMI. Although women in the fifth quintile of waist circumference were at higher risk of colorectal adenomas than those in the first quintile in age-adjusted models, the OR was no longer significant after multivariate adjustment (OR: 1.25, 95% CI: 0.94, 1.67) .

Conclusions: We did not find an association of either BMI or waist circumference with colorectal adenomas among African-American women. Our results support the findings from other studies in primarily White women that showed no association of BMI with colorectal adenoma in women. Although the association of waist circumference with adenoma risk was stronger compared to BMI among African-American women in our study, it was not statistically significant. Further research is needed to confirm these findings, and explore the association of BMI and waist circumference with colorectal adenoma in African-American men.

Citation Format: Chiranjeev Dash, Julie R. Palmer, Lynn Rosenberg, Jeffrey Yu, Lucile L. Adams-Campbell. Body mass index, waist circumference, and the risk of colorectal adenomas: Black Women's Health Study. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr A46.