Abstract 4822: Prospective cohort studies of bowel movement frequency and laxative use and colorectal cancer incidence in US women and men.

Background: It has been estimated that approximately 15-20% of US adults suffer from constipation and a similar proportion of individuals use laxatives. Infrequent bowel movements may increase colorectal cancer risk by increasing concentration and contact time of potential carcinogens in the large bowel. Given that colorectal cancer remains the third most common cancer in US adults, any association between this cancer and bowel movement frequency or laxative use has public health implications. However, the associations between bowel movement frequency, laxative use and colorectal cancer incidence remain uncertain. The case-control studies that assessed information on bowel movement and laxative use after cancer developed may subject to potential bias since disease status may have influenced bowel movement frequency or use of laxatives. Prior limited cohort studies have generally focused on the assessments of bowel movement frequency or laxative use relatively shortly before the colorectal cancer diagnosis. To date, no previous studies have accounted for the potential important latency between bowel movement frequency and laxative use and colorectal cancer onset. Method: We prospectively examined these associations among 88,173 women in the Nurses’ Health Study (1982-2010) and 23,722 men in the Health Professionals Follow-up Study (2000-2010). Cox proportional hazards regression models were used to estimate multivariable hazard ratios (HRs, 95%CIs). We conducted time lagged analyses to evaluate the potential latency. We adjusted for age, smoking, history of colorectal cancer and endoscopy, aspirin use, body mass index, physical activity, postmenopausal hormone use (women only), alcohol consumption, intakes of red meat and processed meat, calcium, folate, fiber, and vitamin D. Results: We documented 2,012 incident colorectal cancer cases during up to 28 years of follow-up. In both men and women, age-adjusted results were essentially the same as multivariable-adjusted results. The multivariable HRs (95%CIs) for infrequent bowel movement (every 3 days or less) relative to daily were 0.86 (95%CI: 0.71-1.04) in women and 0.81 (95%CI: 0.48-1.37) in men. The HRs for weekly to daily relative to never laxative use were 0.98 (95%CI: 0.81-1.20) in women and 1.41 (95%CI: 0.96-2.06) in men. In women, the HRs for every 3 days or less bowel movement relative to daily were 0.87 (95%CI: 0.59-1.27) for colorectal cancers that developed within 10 years of assessment, 1.03 (95%CI: 0.85-1.26) for 11-18 years after assessment, and 0.73 (95%CI: 0.54-1.01) for 19-28 years after assessment. The corresponding HRs for weekly to daily relative to never laxative use were 0.93 (95%CI: 0.63-1.37), 1.03 (95%CI: 0.74-1.44), and 0.98 (95%CI: 0.71-1.35), respectively. Conclusion: Bowel movement frequency and laxative use were not associated with colorectal cancer risk in this study. Citation Format: Xuehong Zhang, Kana Wu, Eunyoung Cho, Jing Ma, Andrew T. Chan, Xiang Gao, Walter C. Willett, Charles S. Fuchs, Edward L. Giovannucci. Prospective cohort studies of bowel movement frequency and laxative use and colorectal cancer incidence in US women and men. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4822. doi:10.1158/1538-7445.AM2013-4822