Dietary Fiber Intake in Young Adults and Breast Cancer Risk

<jats:sec> <jats:title>OBJECTIVE:</jats:title> <jats:p>We evaluated fiber intake during adolescence and early adulthood in relation to breast cancer (BC) risk in the Nurses’ Health Study II.</jats:p> </jats:sec> <jats:sec> <jats:title>METHODS:</jats:title> <jats:p>Among 90 534 premenopausal women who completed a dietary questionnaire in 1991, we documented 2833 invasive BC cases during 20 years of follow-up. In 1998, 44 263 of these women also completed a questionnaire about their diet during high school; among these women, we documented 1118 cases of BC by end of follow-up. Multivariable-adjusted Cox proportional hazards regression was used to model relative risks (RRs) and 95% confidence intervals (CIs) for BC across categories of dietary fiber.</jats:p> </jats:sec> <jats:sec> <jats:title>RESULTS:</jats:title> <jats:p>Among all women, early adulthood total dietary fiber intake was associated with significantly lower BC risk (RR for highest versus lowest quintile 0.81; 95% CI 0.72–0.91; Ptrend = .002). Higher intakes of soluble fiber (RR for highest versus lowest quintile 0.86; 95% CI 0.77–0.97; Ptrend = .02) and insoluble fiber (RR for highest versus lowest quintile 0.80; 95% CI 0.71–0.90; Ptrend &lt; .001) were each associated with lower BC risk. Total dietary fiber intake in adolescence was also associated with lower BC risk (RR for highest versus lowest quintile 0.84; 95% CI 0.70–1.01; Ptrend = .04). For the average of fiber intake during adolescence and early adult life, the RR comparing highest with lowest quintiles was 0.75 (95% CI 0.62–0.91, Ptrend = .004).</jats:p> </jats:sec> <jats:sec> <jats:title>CONCLUSIONS:</jats:title> <jats:p>Our findings support the hypothesis that higher fiber intakes reduce BC risk and suggest that intake during adolescence and early adulthood may be particularly important.</jats:p> </jats:sec>