Should children supplement vitamin D during the winter? Original paper

In this 24-week randomized controlled trial in 189 children (aged 6 to 8) in Denmark, supplemental vitamin D reduced the number of days with acute respiratory tract infections by 17% and the number of days with fever by 43%.

This Study Summary was published on June 4, 2025.

The study

The participants received vitamin D (1,000 IU, or 25 micrograms, per day) or a placebo beginning in August, September, or October. None of the children had a vitamin D deficiency at baseline (defined as less than 12 ng/mL).

The participants also consumed dairy products with varying protein contents during the study, and the effects of protein intake on growth and health outcomes were published separately. This secondary analysis instead focused on the effects of vitamin D on acute respiratory tract infections.

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The results

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This Study Summary was published on June 4, 2025.