Prospective association of 25-hydroxyvitamin d3 and d2 with childhood lung function, asthma, wheezing, and flexural dermatitis.

Higher serum total 25-hydroxyvitamin D (25(OH)D) concentrations have been associated with better lung function and lower risk of allergic disease. 25(OH)D3 constitutes the majority of total 25(OH)D and has been suggested to be more potent than 25(OH)D2. We studied the prospective associations of 25(OH)D2 and 25(OH)D3 with asthma, wheezing, flexural dermatitis, and lung function in children who participated in the Avon Longitudinal Study of Parents and Children-a population-based contemporary birth cohort of children born in 1991-1992 from South West England. Serum 25(OH)D2 and 25(OH)D3 concentrations, measured at a mean age of 9.8 years, were related to incident cases of wheezing (study sample: n = 3,323, 141 cases; 4%), asthma (n = 3,323, 464 cases; 14%), and flexural dermatitis (n = 3,748, 300 cases; 8%), as well as lung function (forced expiratory volume in 1 second [FEV1], forced vital capacity [FVC], and mid-forced expiratory flow assessed at a mean age of 15.5 years: n = 2,259). 25(OH)D2 was inversely associated with flexural dermatitis (adjusted odds ratio per doubling of exposure = 0.83 [95% confidence interval = 0.72-0.94]) and wheezing (0.83 [0.68-1.00]), and 25(OH)D3 was positively associated with flexural dermatitis (1.09 [1.00-1.18]) and wheezing (1.14 [1.03-1.28]). 25(OH)D2 was weakly positively associated with FEV1, and FVC. 25(OH)D3 was not associated with lung function. These results suggest that higher 25(OH)D3 concentrations are associated with increased risk of wheezing and flexural dermatitis. Despite being one of the few prospective studies and being able to adjust for confounders, these findings need replication. Our results do not provide strong evidence that lower concentrations of vitamin D are detrimental to respiratory and allergic health in children.