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.