|Year : 2016 | Volume
| Issue : 2 | Page : 55-56
Vitamin D and asthma
SN Gaur, Gulvir Singh
Department of Pulmonary Medicine, VP Chest Institute, University of Delhi, New Delhi, India
|Date of Web Publication||5-Dec-2016|
S N Gaur
Department of Pulmonary Medicine, VP Chest Institute, University of Delhi, New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Gaur S N, Singh G. Vitamin D and asthma. Indian J Allergy Asthma Immunol 2016;30:55-6
Asthma is a common chronic inflammatory disease affecting an estimated number of 300 million individuals worldwide. It has a significant social and financial burden on public health.  In the developing countries, there has been a rising prevalence of asthma, which is associated with increased urbanization.  The increased prevalence of asthma, as a heterogeneous disease, is not only due to genetics but also may be influenced by a number of environmental factors such as urban lifestyles or dietary habits. Among the numerous proposed hypotheses related to diet, the decrease in serum concentration of Vitamin D supposed to be mainly due to increased time spent indoors and decreased exposure to sunlight; less exercise, obesity, and inadequate calcium intake are of particular interest. ,
Recent epidemiologic studies have shown an association between Vitamin D deficiency and asthma. ,,, Besides the central role of Vitamin D in calcium and bone physiology, the protective effects of Vitamin D in asthma could be attributed to its immunomodulator properties.  In addition, Vitamin D affects the functions of epithelial cell, T- and B-lymphocytes, and antigen-presenting cell functions. Moreover, by induction of regulatory T-cells (Treg) to produce interleukin-10, Vitamin D modulates inflammatory processes and thus could help control asthma severity. 
Evidence from population studies has shown a higher prevalence of Vitamin D deficiency in children with asthma compared with that in controls. Vitamin D insufficiency or deficiency (defined as a 25-hydroxyvitamin D [25(OH)D] level <30 ng/ml) was present in 175 (28%) of 616 children with asthma in Costa Rica,  and serum Vitamin D level was inversely associated with total IgE, eosinophil count, hospitalizations for asthma, use of anti-inflammatory medications, and airway hyperresponsiveness. 
The multiple risk factors for asthma exacerbation include a complex mix of environmental, immunological, and host genetic factors. Epidemiological studies have shown that low serum 25[OH]D3 levels are associated with a higher risk of upper and lower respiratory infections. Vitamin D status has a linear relationship with respiratory infections and lung function, and Vitamin D deficiency (a serum 25(OH)D3 <30 ng/ml) has been associated with severe asthma exacerbation. 
A retrospective analysis was conducted in 92 patients being treated for asthma at the University of New Mexico Adult Asthma Clinic, and serum 25[OH]D3 levels were analyzed in adults with mild to severe persistent asthma. Using multivariant modeling, the relationship was examined between serum Vitamin D levels and the odds of asthma exacerbations ranging in severity from moderate to severe over the span of 5 years. This study demonstrates that Vitamin D sufficiency was significantly associated with a decreased total number of asthma exacerbations, decreased total severe asthma exacerbations, and decreased emergency room visits. 
A question often asked by clinicians is whether patients with asthma should be screened for Vitamin D deficiency or insufficiency. There is no evidence to support such screening for the purpose of asthma management. However, it would be advisable to measure a serum Vitamin D level in children and adults who belong to groups at high risk for Vitamin D deficiency, namely, African Americans, Mexican Americans, and individuals who are obese or have limited sun exposure (e.g., those who are institutionalized).  Vitamin D supplementation is only recommended for patients who have a serum Vitamin D (25[OH]D) level <20 ng/ml because this could compromise their musculoskeletal health.
Future researches are expected to have valuable insights into the role of Vitamin D supplementation in preventing the development of childhood asthma and reducing asthma morbidity. Questions to be addressed in future researches should include (1) whether Vitamin D supplementation protects against viral-like illnesses as well as prevents childhood asthma when given in infancy (with or without supplementation during pregnancy), (2) whether Vitamin D reduces severe asthma exacerbations or improves asthma control (as adjuvant to inhaled corticosteroids) in children of school age, and (3) whether Vitamin D is more effective in members of ethnic minority groups at risk for Vitamin D deficiency.
Vitamin D levels have a definite association with occurrence of various allergic disorders such as asthma, allergic rhinitis, and atopic dermatitis. In the Indian subcontinent, an increase in the prevalence of allergic disorders has been seen due to rapid urbanization. A lack of definite long-term study on Vitamin D in the asthmatic population from India highlights the need for research in this field for further evaluation. However, at present, supplementation of Vitamin D for asthmatics cannot be made a general recommendation.
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