The results of a double-blind randomized and controlled clinical trial evaluating the effect of vitamin D supplementation on acute respiratory tract infections (ARTI) in children living in Northern latitudes were recently published in the European Journal of Nutrition. This was a secondary analysis of a controlled trial investigating vitamin D supplementation as well as varying levels of protein intake on children’s health and growth. Two-hundred healthy white children living in Denmark were included in this analysis, who received either 20 ug/day (800 IU/day) of vitamin D3 or a placebo for 24 weeks.
Baseline 25-OH vitamin D levels were just under 80 nmol/L (~29 ng/mL), a level often considered sufficient and surprising for a Northern latitude, suggesting vitamin D supplementation may have occurred prior to the study’s onset. Levels increased by 9.4 nmol/L among children receiving vitamin D, and decreased by 32.7 nmol/L with placebo. Notably, the study began in late summer/fall, when 25-OH vitamin D levels would be expected to peak before a drop during the winter. Using monthly self-reports from parents, vitamin D supplementation was associated with 17% fewer sick days due to ARTI, and 43% fewer days with ARTI with fever (when compared to placebo).
This falls on the heels of a meta-analysis recently published in The Lancet: Diabetes & Endocrinology, which found that a protective effect of vitamin D did not reach statistical significance. However, a stratified analysis of the studies included in the meta-analysis did find a significant protective effect when considering age, dose, and frequency of supplementation. For example, in trials in which participants were aged 1-15, or given daily vs. weekly/monthly supplements, or given doses between 400-800 IU (not less than 400 IU), a protective effect was observed.