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Open label trial discovers 1,200 IU/day more effective than 400 IU/day in managing influenza in infants

Posted on: January 22, 2018   by  Riley Peterson & John Cannell, MD.


This flu season has been one of the worst in years. According to the CDC, 45 states have reported high rates of flu incidence, which is approximately four times higher than reports from last year. Additionally, though rare, the flu can be life threatening, especially in high risk individuals such as infants, the elderly and immunocompromised individuals.

Infants are at an increased risk for contracting influenza due to the development of their early immune system. As the immune system is first developing in young infants and children, immune cells must encounter many harmful pathogens in order to ‘recognize’ them for later defense. Additionally, because immunity is slowly but gradually strengthening, the influenza vaccine is not approved for infants under six months of age.

So, if the flu vaccine is not an option, or not protective enough for an immunocompromised individual, what can be done to prevent or manage this virus in infants? The CDC is currently recommending frequent handwashing and avoiding contact with infected individuals. Although less well known, vitamin D may offer a possible prevention and management tactic as well. Past research suggests that vitamin D reduces the risk of the cold and flu. Therefore, a recent RCT evaluated the effect of vitamin D supplementation on management of influenza among infants.

The researchers included a total of 400 infants between 3 and 12 months of age who did not have influenza, nor did they develop influenza within one month of the study. Additionally, the participants did not show any evidence of heart, liver or kidney dysfunction.

The infants were randomly assigned to one of two groups: 200 infants received 400 IU vitamin D drops daily for four months, while the other 200 received 1,200 IU vitamin D drops daily for four months. At baseline and every two months, serum vitamin D and calcium levels were measured in all participants. Infants who were diagnosed with influenza were treated accordingly.

This is what the researchers found:

  • Of 121 cases in total, 78 and 43 cases of influenza A infection occurred in the 400 IU/day and 1200 IU/day vitamin D groups, respectively (p = 0.0001)
  • In the cases of influenza, fever duration was shorter in the higher dose vitamin D group than in the low dose vitamin D group (p = 0.0161).
  • Coughing duration of those with influenza was shorter in the higher dose group compared to the low dose group (p < 0.0001).
  • Wheezing duration was shorter in the higher dose vitamin D group compared to the low dose group (p = 0.0018).
  • Four infants showed signs of potential toxicity, but after analysis, this was due to gastrointestinal infection, not vitamin D supplementation.

The researchers concluded:

“Notably, the viral loads of influenza A in infants in the high-dose vitamin D group decreased more rapidly compared to those of infants in the low-dose vitamin D.”

They continued,

“These results suggested that high-dose vitamin D treatment exerted an antiviral effect to promote recovery.”

Now, with the current flu season affecting so many individuals, it seems necessary to take precautionary measures to protect those most vulnerable around us. The Vitamin D Council recommends supplementing infants with 1,000 IU/day (25 mcg) with an upper limit of 2,000 IU (50 mcg). According to this study, 1,200 IU/day (30 mcg) was safe and effective in helping mediate influenza symptoms in 3-12 month old infants, which is consistent with our recommended ranges.

Additionally, as mentioned before, a meta-analysis in the British Medical Journal has shown vitamin D reduced risk of the cold and flu. For adult individuals, the Vitamin D Council recommends supplementing with at least 5,000 IU (125 mcg) and up to 10,000 IU (250 mcg) per day. Though this relationship is not yet set in stone, we do know vitamin D has an active role in the immune system, therefore, action is warranted in order to potentially protect oneself from this nasty flu season. Stay well everyone!


Peterson, R. & Cannell, JJ. RCT discovers 1,200 IU more effective than 400 IU in managing influenza in infants. The Vitamin D Council Blog & Newsletter, 1/2018.


Zhou, J. et al. Preventive Effects of Vitamin D on Seasonal Influenza A in Infants: A Multicenter, Randomized, Open, Controlled Clinical Trial. Pediatric Infectious Disease Journal, 2018.

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