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DO IT Trial: Vitamin D Outcomes and Interventions in Toddlers
Dr. Jonathon Maguire, St. Michael’s Hospital

What was the study about?

There is consistent evidence that many North American children older than 1 year have vitamin D serum levels lower than the recommendations. Data from the 2001-2004 National Health and Nutrition Examination Survey (NHANES) indicated that 65-70% of children had vitamin D levels <75 nmol/L.

However, it is not known what health benefits would be realized if children reached these levels. Observational data has demonstrated an association between low wintertime vitamin D levels and increased risk of viral upper respiratory tract infection (URTI), asthma-related hospitalizations and use of anti-inflammatory medication. However, it is not currently known whether vitamin D supplementation mediates UTRI risk and risk of asthma exacerbations in preschoolers.


A randomized controlled trial is urgently needed to determine whether wintertime vitamin D supplementation could result in reductions in viral URTI and asthma, two of the most common and costly illness of early childhood.


What was the study's goal?

This study will determine whether wintertime ‘high dose’ vitamin D supplementation (2000 IU/day) vs. the ‘standard dose’ (400 IU/day) can prevent laboratory confirmed URTIs and asthma exacerbations during the winter in preschool aged children. We also aim to assess the effect of ‘high dose’ wintertime vitamin D supplementation on vitamin D serum levels as well as RSV, adenovirus and influenza viruses as causes of URTI.


Children will be randomized to the ‘standard dose’ or ‘high dose’ oral supplemental vitamin D for a minimum of 4 months (200 children per group). Parents will obtain a nasal swab from their child with each URTI, report the number of asthma exacerbations and complete symptom checklists. Unscheduled physician visits for URTIs and asthma exacerbations will be recorded. By May, a blood sample will be drawn to determine vitamin D serum levels.


Why was the study important?

Identifying whether vitamin D supplementation of preschoolers can reduce wintertime viral URTIs and

asthma exacerbations and what dose is optimal may reduce population wide morbidity and associated health care and societal costs. This information will assist in determining practice and health policy recommendations related to vitamin D supplementation in healthy Canadian preschoolers.

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