Background: Previous studies have demonstrated that vitamin D affects T-cell function and maturation via the vitamin D receptor. However, no studies in children have been performed on this topic. Because most of the T-cell memory is formed in the first 5 years of life, we aimed to determine the association between serum 25-hydroxyvitamin D (25(OH)D) levels and numbers of circulatory naive, central memory (Tcm), and effector memory (Tem) T lymphocytes in a large population of healthy children. Methods: Among 3189 children participating in a population-based prospective cohort, we measured 25(OH)D levels and performed detailed immunophenotyping of naive and memory T lymphocytes at a median age of 6.0 years (95% range 5.7-7.9). Detailed lymphocyte subsets were available in 986 children. Multivariable linear regression analyses were performed to determine the association between 25(OH)D and the maturation of T lymphocytes in children adjusted for cord blood 25(OH)D levels, herpes seropositivity, sociodemographic and lifestyle confounders. Furthermore, multivariable logistic regression analyses were performed to determine associations between 25(OH)D and childhood infections. Results: Higher 25(OH)D levels were associated with higher numbers of Tem lymphocytes. Every 10 nmol/L higher 25(OH)D was associated with 2.20% (95% CI 0.54-3.89; P=.009) higher CD4TemRA, 1.50% (95% CI 0.38-2.62; P=.008) higher CD4TemRO, and 1.82% (95% CI 0.11-3.56; P=.037) higher CD8TemRA cell numbers. Generally, stronger associations were observed among boys. 25(OH)D levels were not significantly associated with naive, Tcm cell numbers, herpes seropositivity, or URTIs. Conclusions: Our results suggest that vitamin D enhances cellular immunity in young children.

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Keywords Adaptive immune system, Calcitriol, Child, T lymphocytes, Vitamin D
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Journal Pediatric Allergy and Immunology
Looman, K.I. (Kirsten I.M.), Jansen, M.A.E, Voortman, R.G, Van Den Heuvel, D, Jaddoe, V.W.V, Franco, O.H. (Oscar H.), … Moll, H.A. (2017). The role of vitamin D on circulating memory T cells in children: The Generation R study. Pediatric Allergy and Immunology. doi:10.1111/pai.12754