Dietary Fiber Intake in Young Adults and Breast Cancer Risk

Abstract

Objective: We evaluated fiber intake during adolescence and early adulthood in relation to breast cancer (BC) risk in the Nurses' Health Study II.

Methods: 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.

Results: 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 < .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).

Conclusions: 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.

FIGURE 1

Multivariable* RR of BC (and 95% CI) associated with average intake of fiber in adolescence and early adulthood among women in the NHSII. Categories are quintiles of intake. Multivariable model was stratified by age in months at start of follow-up and calendar year of the current questionnaire cycle and was simultaneously adjusted for race (white, nonwhite), family history of BC in mother or sisters (yes, no), history of BBD (yes, no), smoking (never, past, current 1–14/day, current 15–24/day, current ≥25/day), height (<62, 62 to <65, 65 to <68, ≥68 inches), BMI at age 18 years (<18.5, 18.5 to <20.0, 20.0 to <22.5, 22.5 to <25.0, 25.0 to <30.0, ≥30.0), weight change since age 18 (continuous), age at menarche (<12, 12, 13, ≥14 years), parity and age at first birth (nulliparous, parity ≤2 and age at first birth <25 years, parity ≤2 and age at first birth 25 to <30 years, parity ≤2 and age at first birth ≥30 years, parity 3 to 4 and age at first birth <25 years, parity 3 to 4 and age at first birth 25 to <30 years, parity 3 to 4 and age at first birth ≥30 years, parity ≥5 and age at first birth <25 years, parity ≥5 and age at first birth ≥25 years), oral contraceptive use (never, past, current), adolescent alcohol intake (nondrinker, <1.5, 1.5 to <5, 5 to <10, ≥10 g/day), adult alcohol intake (nondrinker, <5, 5 to <15, ≥15 g/day), and adolescent energy intake (quintile). In postmenopausal women, we additionally adjusted for hormone use (postmenopausal never users, postmenopausal past users, postmenopausal current users) and age at menopause (<45, 45–46, 47–48, 49–50, 51–52, ≥53 years). Among all women, we additionally adjusted for hormone use and menopausal status (premenopausal, postmenopausal never users, postmenopausal past users, postmenopausal current users, unknown menopausal status) and age at menopause (premenopausal, unknown menopause, <45, 45–46, 47–48, 49–50, 51–52, ≥53 years). Median of fiber intake for each quintile are 14.8, 17.3, 19.2, 21.4, and 25.3 g/day for all women and premenopausal women; 14.7, 17.2, 19.2, 21.4, and 25.3 g/day for postmenopausal women.