Prenatal and child vitamin D levels and allergy and asthma in childhood.

Background: Early-life vitamin D deficiency may impair immune system development contributing to allergy and asthma onset. Findings from prospective studies are inconsistent.

Objective: To examine whether maternal and child vitamin D levels are associated with allergic and asthma-related symptoms throughout childhood in a Spanish birth cohort.

Methods: 25-Hydroxyvitamin D (25(OH)D) levels were measured in the serum of pregnant women (N = 2525) and children (N = 803). Information on allergic and asthma-related symptoms was obtained from repeated questionnaires from 1 to 9 years.

Results: A total of 19% of mothers and 24% of children had deficient 25(OH)D levels (<20 ng/ml). Higher child 25(OH)D levels at 4 years were associated with lower odds of atopic eczema from 4 to 9 years (adjusted odds ratio = 0.90; 95% CI = 0.84-0.97 per 5 ng/ml). Higher maternal and child 25(OH)D levels were associated with a lower prevalence of late-onset wheezing at the limit of statistical significance (adjusted relative risk ratio (RRR) = 0.86; 95% CI = 0.74-1.00 and RRR = 0.76; 95% CI = 0.58-1.02 per 5 ng/ml, respectively). All the remaining associations were null.

Conclusion: Child 25(OH)D levels at pre-school age are associated with a reduced odds of atopic eczema in later childhood and both maternal and child levels may reduce the prevalence of late-onset wheezing.

Impact: In this Spanish birth cohort, with a total of 19% of mothers and 24% of children with deficient levels of vitamin D, higher child vitamin D at 4 years of age was associated with reduced odds of atopic eczema up to 9 years. There was also some evidence that higher maternal and child vitamin D levels reduced the prevalence of late-onset wheezing. Although these findings need replication, they may imply optimal vitamin D levels at pre-school age to prevent atopic eczema.