Long-term wholegrain intake in line with the Nordic Nutrition Recommendations 2023 and risk of breast cancer in a population-based cohort of women

PURPOSE: Current findings on the relationship between wholegrain intake and breast cancer are inconsistent. We aimed to estimate the association between long-term wholegrain intake and breast cancer risk, specifically investigating: (i) adherence to the updated Nordic Nutrition Recommendations (NNR2023) guidelines on wholegrain intake, and (ii) consumption of specific wholegrain products. METHODS: Data from food frequency questionnaires were used to assess adherence to NNR2023 guidelines on wholegrain intake and consumption of wholegrain products among 36,479 women (48-83 years) in the Swedish Mammography Cohort at two timepoints. Time-updated Cox proportional hazards regression models were used to estimate multivariable-adjusted hazard ratios (HR) and 95% confidence intervals (CI) for incident total breast cancer and hormone receptor-positive and -negative subtypes. RESULTS: During a mean follow-up of 16.5 years, 1,979 breast cancer cases were identified. Compared to long-term low adherence (< 50%, corresponding to < 45 g/day wholegrain intake), the HRs (95% CIs) for women with full adherence (≥ 90 g/day intake) were 0.78 (0.66, 0.94), 0.82 (0.67, 1.03), and 1.08 (0.65, 1.80), for total breast cancer, hormone receptor-positive, and hormone receptor-negative breast cancer, respectively. There was no clear association between long-term consumption of any specific wholegrain products and total breast cancer risk, although HRs for high oatmeal and for high breakfast cereal consumption were < 1, whilst HRs for high crispbread consumption were > 1. CONCLUSION: Wholegrain intake in line with NNR2023 was associated with a lower risk of total breast cancer. However, different wholegrain products may be differently associated with breast cancer risk, indicating the need for further investigation.