Dietary-Based Diabetes Risk Score and breast cancer: a prospective evaluation in the SUN project

An association between type 2 diabetes (T2D) and breast cancer risk has been reported. This association can be potentially explained by alteration of the insulin/IGF system. Therefore, we aimed to prospectively investigate whether a previously reported Dietary-Based Diabetes Risk Score (DDS) inversely associated with T2D was also associated with breast cancer risk in the SUN ("Seguimiento Universidad de Navarra") cohort. We followed up 10,810 women (mean age = 35 years, SD = 11 years) for an average of 12.5 years during which 147 new cases of invasive breast cancer were diagnosed. A validated 136-item FFQ was administered at baseline and after 10 years of follow-up. The DDS (range: 11 to 55 points) positively weighted vegetables, fruit, whole cereals, nuts, coffee, low-fat dairy, fiber, PUFA; while it negatively weighted red meat, processed meats, and sugar-sweetened beverages. The DDS was categorized into tertiles. Self-reported medically diagnosed breast cancer cases were confirmed through medical records. We found a significant inverse association between the intermediate tertile of the DDS score and overall breast cancer risk (Hazard ratio, HR_{T2 vs. T1}= 0.55; 95% CI: 0.36-0.82) and premenopausal breast cancer risk (HR_T2= 0.26; 95% CI: 0.13-0.53), but not for the highest tertile. This association was stronger among women with a BMI < 25 kg/m² (p_interaction: 0.029). In conclusion, moderate adherence to the DDS score was associated with a lower risk of breast cancer, especially among premenopausal women and women with a lower BMI. These findings underscore the importance of antidiabetic diet in reducing the risk of breast cancer.