Introduction Vitamin D deficiency (25-hydroxyvitamin D [25(OH)D]<50 nmol/l) is epidemic in many regions. Recent evidence indicates a possible association between low vitamin D levels and early life allergic disease.
Methods We examined the relationship between cord blood 25(OH)D and atopic dermatitis (AD) in the first 2 years of life in our birth cohort of children born to a predominantly African American population (67.7%) of mothers. Pregnant women living in Detroit, Michigan, USA, and its suburbs were enrolled and their children underwent a standardised physician exam at age 2 years. AD was evaluated by trained physicians.
Results Among children of African American mothers, 87/329 (26.4%) ever had AD while 19/157 (12%) children of White mothers ever had AD. Overall, cord blood 25(OH)D levels were lower in children who ever had AD (geometric means=GM 30.6 vs 35.6 nmol/l, Wilcoxon Rank Sum=WRS p=0.02); but the difference was driven by White children (GM 39.7 vs 50.9 nmol/l, WRS p=0.036) and not African American children (GM 29.4 vs 29.6 nmol/l, WRS p=0.81). The association was also modified by season of birth. Lower 25(OH)D levels were found in children with AD born during summer (GM 35.8 vs 45.2, WRS p=0.02), fall (GM 28.1 vs 33.8, WRS p=0.036) and winter (GM 30.0 vs 33.7, WRS p=0.15), but not spring (GM 30.8 vs 31.4, WRS p=0.90).
Conclusion Cord blood vitamin D is associated with AD at 2 years of age in White but not African American children. The association is also influenced by season of birth.