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

Longitudinal epidemiological data are scarce on the relation between dietary intake of vitamin A and respiratory outcomes in childhood. We investigated whether a higher intake of preformed vitamin A or provitamin β-carotene in mid-childhood is associated with higher lung function and with asthma risk in adolescence. 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 (FEV₁), forced vital capacity (FVC), and forced expiratory flow at 25–75% of FVC (FEF₂₅–₇₅) 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. 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 (95% confidence intervals) for FEV₁ and FEF₂₅–75 were, respectively, 0.21 (0.05-0.38; P-trend 0.008) and 0.18 (0.03-0.32; P-trend 0.02); odds ratios (95% confidence intervals) for FEV₁/FVC ratio below the lower limit of normal and incident asthma were, respectively, 0.49 (0.27-0.90, P-trend 0.04) and 0.68 (0.47, 0.99; P-trend 0.07). 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 CC16 gene polymorphisms. 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.