Seriously? Still with the Vitamin D?

This time they’re trying to prevent upper respiratory infections in kids. I swear, I have no idea who thinks this stuff up. “Effect of High-Dose vs Standard-Dose Wintertime Vitamin D Supplementation on Viral Upper Respiratory Tract Infections in Young Healthy Children“:

Importance: Epidemiological studies support a link between low 25-hydroxyvitamin D levels and a higher risk of viral upper respiratory tract infections. However, whether winter supplementation of vitamin D reduces the risk among children is unknown.

Objective: To determine whether high-dose vs standard-dose vitamin D supplementation reduces the incidence of wintertime upper respiratory tract infections in young children.

Design, Setting, and Participants: A randomized clinical trial was conducted during the winter months between September 13, 2011, and June 30, 2015, among children aged 1 through 5 years enrolled in TARGet Kids!, a multisite primary care practice–based research network in Toronto, Ontario, Canada.

Interventions: Three hundred forty-nine participants were randomized to receive 2000 IU/d of vitamin D oral supplementation (high-dose group) vs 354 participants who were randomized to receive 400 IU/d (standard-dose group) for a minimum of 4 months between September and May.

Main Outcome Measures: The primary outcome was the number of laboratory-confirmed viral upper respiratory tract infections based on parent-collected nasal swabs over the winter months. Secondary outcomes included the number of influenza infections, noninfluenza infections, parent-reported upper respiratory tract illnesses, time to first upper respiratory tract infection, and serum 25-hydroxyvitamin D levels at study termination.

We start, of course, with the epidemiological data that low levels of Vitamin D are associated with higher risks of URIs. I can’t find the absolute risk in the paper, and I’m too tired to go look myself. I assume it’s statistically significant, although I reserve the right to snarkily assume it’s clinically insignificant and probably confounded.

Anyway, it doesn’t matter, because here is the RCT to test the association for causation. Researchers gathered kids age 1-5 years in the winters from 2011-2015 in Canada. They randomized them to get either 2000 IU/d or 400 IU/d of Vitamin D, because I suppose it would be criminal not to supplement everyone with at least some Vitamin D these days. The main outcome of interest was laboratory-confirmed viral URI. Secondary outcomes included individual infections and Vitamin D levels.

More than 700 kids took part in this study, and nearly all completed it (well done, researchers). In the high-dose group, kids got an average 1.05 infections, and in the standard-dose group they got 1.03 infections. Fewer with less Vitamin D, but not statistically significant. There was also no significant differences in the median time to the first laboratory-confirmed infection or the number of parent-reported URIs between groups.

When the study ended, the group getting high-dose Vitamin D had levels of 48.7 ng/mL while the standard-dose group had levels of 36.8 ng/mL, although I’m still unclear on why we should care. The IOM says that anything over 20 ng/mL is “Generally considered adequate for bone and overall health in healthy individuals” and when you get over 50 ng/mL  “Emerging evidence links potential adverse effects to such high levels”.

I do not understand why we keep looking for Vitamin D to be some sort of wonder drug. It’s seriously baffling to me.


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