Vitamin D In the Prevention of Viral-induced Asthma in Preschoolers

Prior treatment

• Intake of oral anti-epileptic, diuretic or anti-fungal medications

Other illness

• Other chronic respiratory disease (e.g. Cystic fibrosis, Bronchopulmonary dysplasia) or chronic kidney, gastrointestinal, endocrinological or cardiac diseases, or sickle cell anemia
• History of bone disorder disease (e.g. rickets, osteomalacia)

Other

• Intake \> 400 IU/day of vitamin D3 supplements or fish oil in the past 3 months
• Intention to use \> 400 IU/day of vitamin D3 supplements or fish oil in the fall and winter
• Extreme prematurity (\< 28 week gestation)
• No vitamin D supplementation (if breast-fed in the last 6 months)
• Vitamin D restrictive diets, that is, minimal intake of vitamin D fortified milk (\<250 mL/day for 1-3 years or \<375 mL/day for 4-6 years AND no other (or \<200 IU/day) vitamin D supplement
• Recent immigrants from regions at high risk of rickets (in the past 12 months)
• Recent refugees (in the past 12 months)
• Undernourished children
• Anticipated difficulty with follow-up or with adherence to the intervention or the procedures

• Age 1-5 years
• Physician-diagnosed asthma (as per the 2015 Canadian Position Paper on the diagnosis of preschool asthma)
• ≥1 asthma exacerbation requiring rescue oral corticosteroids (OCS) in the past 6 months or ≥2 in the past 12 months; or from the pandemic (2020) onwards, ≥1 asthma exacerbation requiring rescue oral corticosteroids (OCS) in the past 12 months (as documented by pharmacy/medical records)
• ≥4 upper respiratory tract infections (URTIs) in the past 12 months (as per parental report); or from the pandemic (2020) onwards, ≥ 2 URTIs in past 12 months
• URTIs as the main asthma trigger (as per parental report)