PURPOSE:Breast cancer (BC) incidence is increasing worldwide. Higher insulin resistance may potentially lead to an increased risk of BC. Sugar-sweetened beverages (SSB) are an acknowledged dietary factor that increases insulin resistance. However, the association between SSB and BC has not been widely explored. We evaluated the association between baseline consumption of SSB and the incidence of BC among relatively young women in a cohort of Spanish university graduates. METHODS:We evaluated 10,713 middle-aged, Spanish female university graduates (median age 33) from the Seguimiento Universidad de Navarra (SUN) cohort, initially free of BC. SSB consumption was collected at baseline using a validated 136-item semi-quantitative food-frequency questionnaire. Incidence of BC was confirmed by a trained oncologist using medical records. We fitted Cox regression models to assess the relationship between baseline categories of SSB consumption and the incidence of BC during follow-up. We stratified the analyses by menopausal status. RESULTS:During 106,189 person-years follow-up, 100 incident cases of BC were confirmed. Among postmenopausal women, regular consumption of SSB was associated with a significantly higher incidence of BC (HR 2.12; 95% CI 1.02, 4.41) in the fully adjusted model, compared to women who never or seldom consumed SSB. No association was found among premenopausal women (HR 1.16; 95% CI 0.66, 2.07). CONCLUSIONS:Even though the number of cases was small, in this Mediterranean cohort, we observed a direct association between SSB consumption and BC risk among postmenopausal women. Nonetheless further larger longitudinal studies are needed to support this association.