Background  Total dietary antioxidant capacity has been associated with a lower risk of breast cancer​, but the supporting evidence is limited. We investigated the association between dietary Non-Enzymatic Antioxidant Capacity (NEAC), measuring the total antioxidant potential of the diet, and the risk of breast cancer.

Methods  We followed 24,950 women recruited into the Swedish National March Cohort through record linkages to Swedish health registries from 1997 until 2016. Total NEAC was computed based on the baseline 96-item food frequency questionnaire. Three measures of dietary NEAC were assessed: total NEAC, NEAC from fruits and vegetables and NEAC from grains. We fitted multivariable Cox proportional hazards regression models to compute hazard ratios (HRs) and 95% confidence intervals (CIs) to quantify the association between dietary NEAC and risk of overall, as well as pre- and post-menopausal breast cancer.

Results  During a median follow-up of 19.2 years, 1142/24,950 women were diagnosed with breast cancer (136/10,826 pre- and 975/21,152 post-menopausal). Findings indicated a trend in the association between total NEAC and the hazard of overall breast cancer (highest vs. lowest quartile: adjusted HR = 0.85, 95% CI 0.69-1.04; p-value for Wald test = 0.138, p-value for trend = 0.048). The association was more evident for post-menopausal breast cancer (HR = 0.76, 95% CI 0.60-0.96; p-value for trend = 0.010). However, when missing data were imputed, the magnitude of the association was found to be weaker in terms of hazard reduction and no statistically significant associations were observed but the direction of the associations remained consistent (overall: HR = 0.89 (0.74-1.08), p-value for trend = 0.091; post-menopausal: HR = 0.84 (0.69-1.03), p-value for trend = 0.057). When distinguishing NEAC based on food sources, breast cancer hazard was inversely associated with NEAC from fruits and vegetables (HR = 0.79, 95% CI 0.64-0.97; p-value for trend = 0.019), but not with NEAC from grains (HR = 1.05, 95% CI 0.86-1.29; p-value for trend = 0.630).

Conclusion  These results suggest an inverse association between dietary total antioxidant capacity and the risk of breast cancer, particularly in post-menopausal women, which seems to be driven by the consumption of fruits and vegetables. However, sensitivity analysis on imputed covariates did not fully confirm our findings, indicating the need for future confirmatory research.