Epidemiological and observational studies have linked vitamin D deficiency with increased asthma/allergy incidence . Vitamin D insufficiency (<75nmol/L) has been associated with increased incidence of severe childhood asthma. Further, high 25(OH)D levels were associated with reduced risk of recent hospitalization, lower use of anti-asthmatic medication and lower airway hyper-responsiveness in childhood asthmatics. The association between vitamin D and allergy and asthma appears to be stronger in children than adults, with some even suggesting that childhood asthma may may be caused by VDD.

Asthmatic children will be recruited in winter. After baseline testing, children will be randomized to take 2,000iu vitamin D or placebo daily for 15 weeks. After the 15 weeks, testing will be repeated. Tests involve blood draws, questionnaires and breathing tests.

Inclusion Criteria:

• Previous clinical diagnosis of asthma
• Ability to perform pulmonary function tests
• Established on anti-asthmatic pharmacotherapy with no expected change

Exclusion Criteria:

• Use of medications that influence vitamin D metabolism or absorption
• Chronic, non-asthma medical issues e.g. endocrine, hepatic, renal, or bone-disease