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Influenza A: 5X reduction in first month (only) with 2,000 IU of vitamin D– RCT July 2014

Effect of Vitamin D Supplement on Influenza A Illness during the 2009 H1N1 Pandemic: A Randomized Controlled Trial

Food Funct., 2014, DOI: 10.1039/C4FO00371C, First published online 14 Jul 2014
Mitsuyoshi Urashima, Hidetoshi Mezawa, Miki Noya and Carlos A. Camargo

In a prior randomized trial, we found that incidence of influenza A was less in vitamin D3 group than among those on placebo, but total incidence of either influenza A or B did not differ between groups.
In this trial, incidence of influenza A or B was less in vitamin D3 group than in placebo group only during the first half of the study.
To elucidate whether vitamin D3 had preventive actions against influenza A, we conducted another trial during the 2009 pandemic of the H1N1 subtype of influenza A.
Students (n=247) of a Japanese high school were randomly assigned to receive vitamin D3 supplements (n=148; 2000 IU/day) or placebo (n=99) in double-blind setting for 2 months.
The primary outcome was incidence of influenza A diagnosed with rapid influenza diagnostic test by medical doctors. Influenza A was equally likely in the vitamin D3 group (20/148: 13.5%) compared with placebo group (12/99: 12.1%).

By post hoc analysis, influenza A occurred significantly less in vitamin D3 group (2/148: 1.4%)
compared with placebo group (8/99: 8.1%) (risk ratio, 0.17; 95% confidence interval, 0.04 to 0.77; P=0.009) in the first month.
However, during the second month, vitamin D3 group experienced more events and effectively caught up with the placebo group. Vitamin D3 supplementation did not lower overall incidence of influenza A during the 2009 H1N1 pandemic. A post hoc analysis suggests that the initial benefit during the first month of treatment was lost during the second month.

Perhaps more benefit if:

  1. More daily vitamin D
  2. Loading dose initially

See also Vitamin D Life

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