May 4, 2009 — Vitamin D insufficiency is linked to asthma severity, according to the results of a cross-sectional study reported in the May 1 issue of the American Journal of Respiratory and Critical Care Medicine.
"Maternal vitamin D intake during pregnancy has been inversely associated with asthma symptoms in early childhood," write Erick Forno, from Brigham and Women's Hospital in Boston, Massachusetts, and colleagues. "However, no study has examined the relationship between measured vitamin D levels and markers of asthma severity in childhood."
The goal of this study was to evaluate the association between measured levels of 25-hydroxyvitamin D ([25(OH)D]; the predominant circulating form of vitamin D) and markers of asthma severity and allergy in 616 Costa Rican children aged 6 to 14 years. Univariate and multivariate analyses were performed with use of linear, logistic, and negative binomial regressions. Increased airway responsiveness was defined as a 8.58-µmol or less provocative dose of methacholine producing a 20% decrease in baseline forced expiratory volume in 1 second.
Levels of vitamin D were insufficient (< 30 ng/mL) in 175 (28%) of 616 children with asthma. Vitamin D levels were significantly and inversely associated with total immunoglobulin E (IgE) and eosinophil count, based on multivariate linear regression models. A log10-unit increase in vitamin D levels was associated with lower odds of any hospitalization in the previous year (odds ratio [OR], 0.05; 95% confidence interval [CI], 0.004 - 0.71; P = .03), any use of anti-inflammatory medications in the previous year (OR, 0.18; 95% CI, 0.05 - 0.67; P = .01), and increased airway responsiveness (OR, 0.15; 95% CI, 0.024 - 0.97; P = .05), according to multivariate logistic regression models.
"Our results suggest that vitamin D insufficiency is relatively frequent in an equatorial population of children with asthma," the study authors write. "In these children, lower vitamin D levels are associated with increased markers of allergy and asthma severity."
Limitations of this study include debate regarding what constitutes a normal circulating vitamin D level, lack of a control group, cross-sectional design, and possible residual confounding by socioeconomic status.
"Our data suggest that additional work needs to be done to determine the potential beneficial role that vitamin D might play, if any, in established human allergy and asthma," the study authors conclude. "These studies should include in vitro and animal studies to further elucidate the mechanisms for the role of vitamin D, and eventual clinical trials of vitamin D supplementation to prevent exacerbations. In addition, common polymorphisms in the vitamin D receptor and other genes in the vitamin D pathway should be further characterized, especially as they relate to circulating vitamin D levels and asthma severity."
In an accompanying editorial, Graham Devereux, MD, from the University of Aberdeen in Aberdeen, United Kingdom, and colleagues discuss the difficult scientific, ethical, and regulatory issues involved in intervention studies of vitamin D in the primary prevention and treatment of asthma.
"Studies that supplement with the currently recommended doses of vitamin D, while unlikely to raise ethical or regulatory concerns, would fail to address the scientific evidence that larger vitamin D intakes (e.g., 2,000 IU/d) may be required for beneficial nonskeletal effects," the editorialists write. "While these concerns may be satisfactorily addressed, it remains to be seen whether pregnant women, parents, or patients will be similarly convinced and participate in such studies. Ultimately, it is only by investigating the effects of vitamin D in doses at, and above those currently recommended, that decisions can be made on the optimal intake of vitamin D for health and the possible prevention and treatment of asthma."
The National Institutes of Health supported this study. One of the study authors has been a consultant to DiaSorin Corporation. Another study author has disclosed various financial and/or other relationships with AstraZeneca, Boehringer Ingelheim, Genentech, Glaxo-Wellcome, Roche Pharmaceuticals, Pfizer, Schering Plough, Variagenics, Genome Therapeutics, and Merck Frost. The editorialists have disclosed no relevant financial relationships.
Am J Respir Crit Care Med. 2009;179:739-742, 765-771.
Medscape Medical News © 2009 Medscape, LLC
Send press releases and comments to news@medscape.net.
Cite this: Vitamin D Insufficiency Linked to Asthma Severity - Medscape - May 01, 2009.
Comments