Association of vitamin D with respiratory outcomes in Canadian children

and A SenthilselvanBACKGROUND/OBJECTIVES: Vitamin D modifies airway inflammation and appears to be important in building immunity againstrespiratory infections, and so is potentially beneficial in asthma. However, to date results from studies investigating the relationshipof vitamin D with respiratory outcomes are inconsistent. The objective of this study was to determine the association of vitamin Dwith current wheeze, ever asthma and lung function.SUBJECTS/METHODS: Data on 1213 children aged 6–12 years, from the Canadian Health Measures Survey, were considered forthe study. Serum 25-hydroxy vitamin D (25(OH)D) levels were categorized into three categories: ⩽49nmol/l (low); 50–74nmol/l(moderate); and ⩾75nmol/l (high).RESULTS: Children in the low and high 25(OH)D categories were more likely to report current wheeze in comparison to those in themoderate category (odds ratio (OR): 3.26, 95% confidence interval (CI): 1.16–9.17 and OR: 2.14, 95% CI: 1.07–4.28, respectively). Theresults for the association between 25(OH)D levels and ever asthma were similar to those observed for current wheeze, except thata significant association was observed only in the lower category. The rate of increase in forced expiratory volume in one secondand forced vital capacity with age was greater in the moderate category.CONCLUSIONS: Children in both low and high 25(OH)D categories had increased risk of current wheeze and reduced rate ofchange in lung function with age in comparison to the moderate category, raising the possibility of a U-shaped associationbetween vitamin D levels and respiratory health. Clearer guidelines for optimal vitamin D levels are required to improve respiratoryhealth in children.European Journal of Clinical Nutrition advance online publication, 2 July 2014; doi:10.1038/ejcn.2014.121INTRODUCTIONAsthma is the most common chronic condition affecting childrenin developed countries.