Associations between serum folate and vitamin D levels and incident mouse sensitization in adults

Background: Although both folic acid intake and vitamin D levels are hypothesized to be contributors to the increased incidence of allergic diseases, prospective studies of these relationships have not been done in adults. Objectives: We sought to determine whether serum folate or vitamin D levels are associated with incident mouse sensitization among new workers at a mouse facility. Methods: Subjects started employment at the Jackson Laboratory between June 2004 and July 2007. Skin testing to mouse and other allergens and collection of questionnaire data were performed at baseline and every 6 months. Serum folate and vitamin D levels were assessed on baseline samples stored at -80 degrees C. Folate was categorized into tertiles (2.5-10.5, 10.5-16.2, and 16.2-78.4 ng/mL, respectively). Vitamin D was categorized as less than 20 ng/mL, 20 to 29 ng/mL, or 30 ng/mL or greater. This was a nested case-control study in which 5 control subjects were matched to each case on baseline atopy and type of employment. Multivariate analyses controlled for age, sex, education, smoking, season, personal mouse exposure, and serum folate and vitamin D levels. Results: Thirty-five cases and 47 control subjects were included. The odds of incident mouse sensitization were higher in the intermediate and highest tertiles of serum folate compared with the lowest tertile of serum folate (odds ratio of 10.5 [95% CI, 1.8-61.5; P=.009] and odds ratio of 5.6 [95% CI, 1.8-31.3; P=.049], respectively, in the multivariate model). Serum vitamin D levels were not associated with incident mouse sensitization. Conclusions: These findings support a role for higher serum folate levels in increased risk of incident allergic disease, even during adulthood.