To the Editor Ms Aglipay and colleagues1 found that daily high-dose (2000 U) oral vitamin D was not superior to maintenance (400 U) doses for preventing winter season viral upper respiratory tract infections in healthy young children. They could not ethically use a placebo control. Although the mean baseline vitamin D level was approximately 36 ng/mL for both treatment groups, almost a third had baseline levels less than 30 ng/mL (to convert serum 25-hydroxyvitamin D from ng/mL to nmol/L, multiply by 2.4960). In another study that randomized children whose baseline levels were all lower than 26 ng/mL, children with the very lowest baseline levels (3-11 ng/mL) in the high-dose supplement group had significantly reduced moderate-severe asthma attacks during the first 3 months but no difference during the overall prolonged study period.2 Supplementation, high-dose or maintenance, likely exerts its effect on steady state within 8 weeks.3,4 After that, maintenance and high-dose treatment groups may not differ in clinical event rates.
Davidson BL, Alansari K. Vitamin D Supplementation and Upper Respiratory Tract Infections in Children. JAMA. 2017;318(21):2138–2139. doi:10.1001/jama.2017.15150
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