A study that was published in Allergy, Asthma & Immunology Research (2013 Sept; 5(5): 283-8) looked at the relationship between vitamin D levels and asthma severity. Researchers analyzed 25-hydroxyvitamin D levels in serum collected from 121 asthmatic adults from Costa Rica to investigate the association between vitamin D levels and the severity of their disease. Vitamin D levels below 30 ng/mL, we defined as insufficient. Asthma severity was determined by forced expiratory volume in 1 second (FEV1), and forced vital capacity (FVC). When the population was stratified by vitamin D status, 91% of asthmatic patients with vitamin D levels below 20 ng/mL (n=36) and 74% of patients with vitamin D levels between 20 and 30 ng/mL (n=73) had severe asthma versus 50% of those with vitamin D sufficiency (n=12; P=0.02). Vitamin D insufficiency was associated with a higher risk of severe asthma. High vitamin D levels were associated with a lower risk of hospitalization or emergency department visit during the last year.

A cross-sectional, case-control study was published in the Journal of Pediatrics (Volume 156, Issue 6, June 2010) looked at 113 African American children (between six and 20 years of age) and compared vitamin D levels in those with asthma and those without asthma. Vitamin D deficiency was found in 86% of the asthmatic subjects as compared to 19% in the control group.

Other research, published in the Journal of Pediatrics (published online Sept 25, 2010) and involving Italian children produced similar results. Only 9.4% of the 75 children with asthma had adequate vitamin D levels. Furthermore, low vitamin D levels correlated with poorer breathing capacity (forced vital capacity percent and the Childhood Asthma Control Test).

The Journal of Allergy and Clinical Immunology (Volume 126, Issue 1 , Pages 52-58.e5, July 2010) looked at vitamin D levels in 1,024 children with mild to moderate asthma. Vitamin D (25(OH)D) levels were below 30 ng/ml in 35% of the subjects. Also, poor vitamin D status was associated with an increased risk of hospitalization or needing to go to the emergency room.