Dietary Iron Intake in Relation to Age at Menarche: A Prospective Cohort Study in Chilean Girls

Abstract

BackgroundEarly onset of menarche is considered an important risk factor for a number of diseases in adulthood. Iron intake may be related to pubertal timing because of its role in childhood growth and reproductive function. ObjectiveWe investigated the relation between dietary iron intake and age at menarche in a prospective cohort of Chilean girls. MethodsOverall, 602 Chilean girls were included in the Growth and Obesity Cohort Study, a longitudinal study that began in 2006 when the girls were 3–4 y old. Starting in 2013, diet was assessed every 6 mo through 24-h recall. The date of menarche was reported every 6 mo. Our analysis included 435 girls with prospective data on diet and age at menarche. We used a multivariable Cox proportional hazards regression model with restricted cubic splines to estimate HRs and 95% CIs for the association between cumulative mean iron intake and age at menarche. ResultsMost girls (99.5%) attained menarche with a mean (standard deviation) age at menarche of 12.2 (0.9) y. The mean dietary iron intake was 13.5 (range: 4.0–30.6) mg/d. Only 3.7% of girls consumed below 8 mg/d, the RDA. After multivariable adjustment, cumulative mean iron intake had a nonlinear association with menarche (P-for-nonlinearity: 0.02). Iron intakes above the RDA, between 8 and 15 mg/d, were associated with progressively lower probability of earlier menarche. Above 15 mg/d, the HRs were imprecise but tended to approach the null as iron intake increased. This association was attenuated after adjusting for girls’ BMI and height before menarche (P-for-nonlinearity: 0.11). ConclusionIn Chilean girls, iron intake during late childhood, independent of body weight, was not an important determinant of menarche timing.