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Am Fam Physician. 2017;96(5):290-291

Author disclosure: No relevant financial affiliations.

Clinical Question

Does the use of vitamin D improve asthma symptoms and reduce asthma exacerbations requiring corticosteroid treatment?

Evidence-Based Answer

Despite the authors' caution that further data are needed to clarify the role of vitamin D in care, this Cochrane review found that its use reduces the average number of asthma exacerbations requiring corticosteroid treatment from 0.44 to 0.28 per person per year. It also decreases the risk of emergency department visits and hospitalizations due to asthma exacerbation from 6% per year to around 3% per year.1 (Strength of Recommendation: A, based on high-quality evidence.) Vitamin D has no effect on asthma symptom control as measured by the Asthma Control Test or on lung function as measured by predicted forced expiratory volume in one second (FEV1).1 (Strength of Recommendation: A, based on high-quality evidence.) Family physicians should await further studies and updated guidelines before recommending the use of vitamin D for this indication.

Practice Pointers

Asthma is a chronic inflammatory small airway disease characterized by recurrent episodes of dyspnea, wheezing, cough, and chest tightness (commonly known as asthma exacerbations). Asthma affects all age groups, with a prevalence of 8.4% in children and 7.6% in adults in the United States.2 Exacerbation is a major cause of morbidity and mortality in persons with asthma. An exacerbation is classified as severe when the treatment includes systemic corticosteroids, emergency department visits, or hospitalization.3 Vitamin D levels are often low in patients with asthma, and this has been linked to an increased risk of exacerbation.4,5 Vitamin D has been shown to induce antimicrobial activity 6 and anti-inflammatory activities.7 It also enhances responsiveness to inhaled corticosteroids in patients with asthma.8 The authors of this review sought to determine if use of vitamin D prevents asthma exacerbations and improves asthma symptoms.

This Cochrane review included nine double-blind, placebo-controlled trials that lasted at least 12 weeks.1 Seven studies involved 435 children and two studies involved 658 adults for a total of 1,093 participants. Most of the participants had mild or moderate persistent asthma, and a minority had severe asthma.

Oral administration of vitamin D3 (cholecalciferol) significantly decreased asthma exacerbations requiring systemic corticosteroid treatment. The average number of exacerbations per person per year decreased from 0.44 to 0.28 with vitamin D; in other words, a patient treated with vitamin D gained more than one year (from one event every 2.2 years to one event every 3.5 years) between exacerbations (relative risk = 0.63; 95% confidence interval [CI], 0.45 to 0.88). Vitamin D also significantly decreased emergency department visits and hospitalizations due to asthma exacerbation (absolute risk reduction = 3.8%; 95% CI, 1.3% to 5%; number needed to treat = 27 [95% CI, 20 to 76]).

Vitamin D had no effect on daily asthma symptom control, the use of inhaled beta agonists, predicted FEV1, peak expiratory flow rate, or the incidence of serious adverse events. Given that there were no fatalities in the trial, mortality data were not calculated.

Trials conducted in adults contributed disproportionately to this analysis. There was considerable heterogeneity in the vitamin D3 regimens used in the studies, with dosages ranging from 400 to 4,000 IU daily (median dosage = 900 IU daily) with or without an additional 100,000 IU bolus dose in several studies. Formulations of 1,000 IU taken weekly, 60,000 IU monthly, or 120,000 IU bimonthly were used in other studies. Further research is needed in children and to determine whether baseline and circulating 25-hydroxyvitamin D concentrations influence the effect of this therapy.

The Endocrine Society clinical guideline suggests that infants and children at risk of vitamin D deficiency may require a daily vitamin D supplement of at least 1,000 IU, and adults may need at least 1,500 to 2,000 IU.9 Currently, no published guidelines discuss the use of vitamin D in the management of asthma.

The practice recommendations in this activity are available at

These are summaries of reviews from the Cochrane Library.

This series is coordinated by Corey D. Fogleman, MD, assistant medical editor.

A collection of Cochrane for Clinicians published in AFP is available at

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