Vitamin D deficiency in childhood and asthma susceptibility: is infancy a crucial period?

Published Online: October 7, 2016

Asthma development in genetically susceptible children is a multifactorial process driven by environmental factors, particularly respiratory infections and airborne allergens. Airway inflammatory responses to these environmental agents during the first years of life can act both independently and synergistically to trigger initial asthma onset, and to subsequently consolidate the disease over the preschool years. A potential co-factor implicated in this process is deficiency in vitamin D, the active form of which regulates immune function and lung development. However, as the majority of studies in this field have measured vitamin D at a single age, precise data on the relative impact of vitamin D deficiency at different ages and disease stages is lacking.

In a recent issue of in The Journal of Allergy & Clinical Immunology (JACI), Hollams and colleagues report for the first time a study tracking vitamin D levels in a birth cohort of high-risk children followed prospectively to age 10 years, including rigorous monitoring of respiratory infections and atopy-associated phenotypes.  Vitamin D deficiency was relatively common during winter and spring up to age 4, and for each subject the total number of recorded instances of deficiency was positively associated with their risk for asthma at age 10. Moreover within the first 3 years allergic sensitization was inversely related to vitamin D concentration, and regression analyses suggested that this may be a major pathway via which vitamin D influences asthma risk. In addition, children who were vitamin D deficient at 6 months showed increased nasopharyngeal colonization with Streptococcus and earlier onset of severe lower respiratory infections.

This study identifies the first 1-2 years as a vulnerable period during which inadequate vitamin D may set susceptible children on a course for asthma, by increasing risk for allergic sensitisation and severe lower respiratory infection. This question of whether direct supplementation (or perhaps controlled healthy sun exposure) during this early postnatal window could mitigate risk for any or all of these inter-related clinical phenotypes can only be answered by prospective trials, which based on these findings should encompass the infant period.

The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.
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