> ## Content Index
> Fetch the complete content index at: https://www.foodconsumer.org/llms.txt
> Use this file to discover other available public pages before exploring further.

# Vitamin D may prevent some but not all sorts of influenza illness
- URL: https://www.foodconsumer.org/vitamin_d_influenza_0117150434/
- Published: 2015-01-17T17:32:00.000Z
- Updated: 2026-09-22T16:10:37.000Z
- Description: In a Japanese trial, high school students taking 2,000 IU of vitamin D3 daily had about the same overall influenza A rate as those on placebo, 13.5 against 12.1 percent, during the 2009 H1N1 pandemic. The vitamin D group had fewer cases in month one but more in month two.
- Author: Food Consumer
- Tags: Vitamins, Nutrition, #vivvo-import

Saturday Jan 17, 2015 (foodconsumer.org) -- Vitamin D has been touted by many as a wonder treatment or preventative for more than 100 medical conditions. Indeed, vitamin D has been associated with many diseases. And laboratory studies have even proved that vitamin D is needed to produce certain antibacterial peptides, which are important for innate immunity against microbial and viral infections such as influenza or flu.

But in terms of its anti-flu efficacy, vitamin D may not be omnipotent against all sorts of influenza viruses. A Japanese study published in 2014 in Food Function shows evidence suggesting that supplementation with 2000 IU of vitamin D3 per day could not prevent influenza A during the 2009 pandemic of the H1N1 subtype of influenza A. 

M. Urashima at Jikei University School of Medicine in Tokyo Japan and colleagues compared students of a Japanese high school who received vitamin D3 supplements in a dose of 2000 IU per day with those who were assigned to receive placebo for a period of 2 months to see if the vitamin D supplementation would make any difference in incidence of influenza A. A rapid diagnostic test for influenza was performed by medical doctors.

Incidence of influenza A in the vitamin D supplemented group was the same as that in the placebo group, 13.5% versus 12.1%. However, in the first month of the 2-month trial, the incidence of influenza A was found significantly lower in the vitamin D3 group, compared with that in the control group, 1.4% versus 8.1%. But in the second month, the vitamin D3 group experienced actually more influenza A infections, compared with the control group.

The researchers concluded that "Vitamin D3 supplementation did not lower the overall incidence of influenza A during the 2009 H1N1 pandemic."

It is unknown how in the first month vitamin D3 seemed to be beneficial and in the second month, the supplement seemed to increase the odds of influenza A infections.

Some studies found evidence to suggest that vitamin D is protective against seasonal flu. One study led also by Dr. Mitsuyoshi Urashima and colleagues and published in in the March 10, 2010 issue of American Journal of Clinical Nutrition showed that school children receiving 1200 IU per day of vitamin D3 were 42% less likely to get infected with seasonal flu than those receiving placebo.

The researchers found the antiflu effect more significant among children who had not been taking other vitamin D supplements and who started nursery school after age 3\. The reduction in the incidence of seasonal flu was 64 percent for both groups. Also they found that among children with previously diagnosed asthma, vitamin D supplementation cut the risk of asthma attacks by 83%.

The trial was conducted between Dec 2008 and March 2009.

These two trials together indicate that vitamin D supplementation may protect against some types of influenza viruses but not all. (David Liu,PH.D)

*Urashima M, Mezawa H, Noya M, Camargo CA Jr. Effects of vitamin D supplements on influenza A illness during the 2009 H1N1 pandemic: a randomized controlled trial. Food Funct. 2014 Sep;5(9):2365-70.*

More reads

  
[Could vitamin D work better than influenza vaccine?](https://www.foodconsumer.org/vitamin%5Fd%5Fwork%5Fbetter%5Fthan%5Finfluenza%5Fvaccine%5F2210100543/)  
[Vitamin D3 as effective as influenza vaccine - study](https://www.foodconsumer.org/vitamin%5Fd3%5Fas%5Feffective%5Fas%5Finfluenza%5F0118130201/)  
[Vitamin D supplementation lowers infection risk](https://www.foodconsumer.org/vitamin%5Fd%5Finfection%5F1228131042/)  
[Can we enlist vitamin D to fight flu pandemic?](https://www.foodconsumer.org/can%5Fwe%5Fenlist%5Fvitamin%5Fd%5Fto%5Ffight%5Fflu%5Fpandemic%5F2504100355/)