Repeated measurements of serum carotenoid, retinol and tocopherol levels in relation to colorectal cancer risk in the Women's Health Initiative

Background/Objective: Previous cohort studies examining the association of serum antioxidant levels and risk of colorectal cancer have used a single (baseline) measurement only. In the present study, we assessed the association of serum levels of eight antioxidant nutrients in relation to risk of colorectal cancer, using repeated measurements. Subjects/Methods: Data on a subsample of women in the Women's Health Initiative with repeated measurements of serum retinol, alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein + zeaxanthin, lycopene, alpha-tocopherol and gamma-tocopherol during follow-up were included in the analysis. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CIs). Results: Among 5477 women with baseline serum antioxidant values, 88 incident cases of colorectal cancer were identified over a median follow-up time of 12 years. Serum antioxidants measured at baseline generally showed no association with risk of colorectal cancer, although serum beta-carotene at baseline showed a non-significant inverse association with colon cancer alone. Furthermore, using the repeated measurements of beta-carotene, the average of all measurements was inversely associated with risk of both colorectal and colon cancer: HRs for highest vs lowest tertile 0.54, 95% CI 0.31-0.96, and 0.47, 95% CI 0.25-0.88, respectively. No associations were seen with other antioxidant nutrients in the repeated measure analyses. Conclusions: In this study, baseline levels of antioxidant nutrients were not associated with risk of colorectal or colon cancer; however, using repeated measures, a relatively high serum level of beta-carotene (average of all measurements) was inversely associated with risk of colon and colorectal cancer in postmenopausal women. European Journal of Clinical Nutrition (2012) 66, 549-554; doi:10.1038/ejcn.2011.207; published online 14 December 2011