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Background: The association between vitamin D status at birth and childhood allergic outcomes is uncertain. The desert climate of Tucson offers a unique setting for studying the health effects of higher exposure to vitamin D.

Objective: To assess the relationship between cord blood 25-hydroxyvitamin D (25[OH]D) levels and allergic outcomes through age 5 years.

Methods: Cord blood 25(OH)D levels were measured in 219 participants in the Tucson Infant Immune Study, a population-based birth cohort. Plasma total IgE and specific IgE levels to 6 aeroallergens were measured at 1, 2, 3, and 5 years. Skin prick test (SPT) positivity (wheal diameter >= 3 mm) and physician-diagnosed active allergic rhinitis and asthma were assessed at age 5 years. Longitudinal models were used to assess the relationship between 25(OH)D and IgE levels. Logistic regression models were used to assess the relationship of 25(OH)D level with SPT positivity, allergic rhinitis, and asthma.

Results: The median cord blood 25(OH)D level was 64 nmol/L (interquartile range, 49-81 nmol/L). Relative to the reference group (50-74.9 nmol/L), both low (<50 nmol/L) and high (>= 100 nmol/L) levels were associated with increased total IgE (coefficient = 0.27, P = .006 and coefficient = 0.27, P = .04, respectively) and detectable inhalant allergen-specific IgE (odds ratio = 2.4, P = .03 and odds ratio = 4.0, P = .01, respectively) through age 5 years. High 25(OH)D levels were also associated with increased SPT positivity (odds ratio = 4.0, P = .02). By contrast, the 25(OH)D level was not significantly associated with allergic rhinitis or asthma.

Conclusion: Both low and high levels of cord blood 25(OH)D were associated with increased aeroallergen sensitization. The association between vitamin D status and actual allergic diseases merits further study. (J Allergy Clin Immunol 2011;128:1093-9.)