Background: Basic science literature strongly supports a role of oxidative stress in colorectal cancer (CRC) etiology, but in epidemiologic studies, associations of most individual exposures with CRC have been weak or inconsistent. However, recent epidemiologic evidence suggests that the collective effects of these exposures on oxidative balance and CRC risk may be substantial.
Methods: Using food frequency and lifestyle questionnaire data from the prospective Iowa Women's Health Study (1986-2012), we investigated associations of 11-component dietary and 4-component lifestyle oxidative balance scores (OBS) with incident CRC using multivariable Cox proportional hazards regression.
Results: Of the 33,736 cancer-free women aged 55-69 years at baseline, 1,632 developed CRC during follow-up. Among participants in the highest relative to the lowest dietary and lifestyle OBS quintiles (higher anti-oxidant relative to pro-oxidant exposures), the adjusted hazard ratios (HRs) and their 95% confidence intervals (CI) were, respectively, 0.77 (0.63, 0.94) (Ptrend=0.02) and 0.61 (0.52, 0.71) (Ptrend<0.0001). Among those in the highest relative to the lowest joint lifestyle/dietary OBS quintile, the HR was 0.45 (95% CI 0.26, 0.77).
Conclusions: Our findings suggest that a predominance of antioxidant over pro-oxidant dietary and lifestyle exposures-separately and especially jointly-may be inversely associated with CRC risk among older women.