In 65-70% of North American children over one year, vitamin D levels are dangerously low (<75 nmol/L). Low vitamin D has been linked to an increased risk of viral upper respiratory tract infections (URTI), asthma-related hospitalizations, and the usage of anti-inflammatory medications. Wintertime vitamin D supplementation has not been proven to lessen the risk of URTI and asthma exacerbations, two of the most prevalent and costly illnesses in young children. For this study, scientists focused on comparing the effects of ‘high dose’ (2000 IU/day) vitamin D supplementation vs.’standard dose’ (400 IU/day) vitamin D supplementation in reducing laboratory-confirmed URTI and asthma exacerbations in preschool-aged Canadian children during the winter, and assess the effect of ‘high dose’ vitamin D supplementation on vitamin D serum levels and specific viruses that cause URTI. 

The research was a randomized controlled experiment with a pragmatic approach. Researchers enrolled 750 healthy children aged 1 to 5 years old throughout four winters. TARGet Kids! was a primary healthcare research network that included participating clinicians. For a minimum of four months, children were randomized to receive either “normal dosage” or “high dose” oral supplemental vitamin D (200 children per group). With each URTI, parents collected a nose swab from their child, reported the frequency of asthma exacerbations, and filled out symptom checklists. They documented unscheduled doctor visits for URTIs and asthma flare-ups. A blood sample was obtained by the end of May to test vitamin D serum levels. The primary analysis was done to be a Poisson regression model comparison of URTI rates between study groups. They compared Vitamin D blood levels, asthma exacerbations, and the frequency of certain viral agents between groups in secondary analyses. 

Identifying whether vitamin D supplementation of preschoolers helped to minimize wintertime viral URTIs and asthma exacerbations, as well as the best dose. It helped to reduce population morbidity and associated healthcare and societal expenditures. The data helped to come out as an aid in the development of vitamin D supplementation recommendations for healthy Canadian preschoolers, as well as health policy suggestions.