Dietary intake of vitamin A, lung function and incident asthma in childhood

BACKGROUND: Longitudinal epidemiological data are scarce on the relationship between dietary intake of vitamin A and respiratory outcomes in childhood. We investigated whether a higher intake of preformed vitamin A or pro-vitamin β-carotene in mid-childhood is associated with higher lung function and with asthma risk in adolescence. METHODS: In the Avon Longitudinal Study of Parents and Children, dietary intakes of preformed vitamin A and β-carotene equivalents were estimated by food frequency questionnaire at 7 years of age. Post-bronchodilator forced expiratory volume in 1 s (FEV(1)), forced vital capacity (FVC) and forced expiratory flow at 25–75% of FVC (FEF(25–75%)) were measured at 15.5 years and transformed to z-scores. Incident asthma was defined by new cases of doctor-diagnosed asthma at age 11 or 14 years. RESULTS: In multivariable adjusted models, a higher intake of preformed vitamin A was associated with higher lung function and a lower risk of incident asthma: comparing top versus bottom quartiles of intake, regression coefficients for FEV(1) and FEF(25–75%) were 0.21 (95% CI 0.05–0.38; p(trend)=0.008) and 0.18 (95% CI 0.03–0.32; p(trend)=0.02), respectively; odds ratios for FEV(1)/FVC below the lower limit of normal and incident asthma were 0.49 (95% CI 0.27–0.90; p(trend)=0.04) and 0.68 (95% CI 0.47–0.99; p(trend)=0.07), respectively. In contrast, there was no evidence for association with β-carotene. We also found some evidence for modification of the associations between preformed vitamin A intake and lung function by BCMO1, NCOR2 and SCGB1A1 gene polymorphisms. CONCLUSION: A higher intake of preformed vitamin A, but not β-carotene, in mid-childhood is associated with higher subsequent lung function and lower risk of fixed airflow limitation and incident asthma.