Winter birth in inner-city asthmatic children is associated with increased food allergen sensitization risk

摘要

Vitamin D was characterized as both a continuous variable and as a dichotomous variable using 20 ng/mL as a cutoff on the basis of the distribution of vitamin D within the population. The Pearson x~2 test was used for comparison of categorical data, and the Kruskal-Wallis test was used for testing between quantitative and categorical data: for example, food and environmental allergen sensitization. The relationship between food allergen sensitization and season of birth (winter—December, January, and February; spring—March, April, and May; summer—June, July, and August; fall—September, October, and November) was also examined. Season of birth was analyzed as a proxy for vitamin D levels in the first year of life.6 Because of known differences in vitamin D status and race,7 analyses were performed on the black portion of the population because the overwhelming majority of our population was black (n = 340; Table I). Statistical analyses were performed using R (http:// www.r-project.org/).