Atishoo – that’s D’ one!

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Vitamin D Vs Influenza A

Lets face it, right now we are still recovering from the various revelations about the novel variant H1N1 or swine flu non event (in terms of pandemic effects) to be looking to see if we can manage the more common seasonal influenza. Plus spring is in the air and we all know that colds and the flu viruses seem to be less vigorous during the time of the year we actually see the sun!

However a rather neat randomised trial to see if Vitamin D supplementation had any prevention effect in school children adds further weight to the evolving understanding of its innate immune activation potential.[1]

What did they do?

The researchers followed 167 children in the Vitamin D supplementation group who took 1200iu per day as well as carefully following 167 children in the placebo group. Over a 4 month period from Dec 08 until March 09 this multi centre, randomised, double blind placebo controlled trial ran in Japan via 12 hospitals and 8 doctors.

Aged between 6-15 and carefully selected to exclude history of vitamin D supplementation, or medical conditions such as urinary tract stones, allergy to ingredients or bone metabolism problems, immunosuppressive history or just considered unsuitable by the clinician in charge.

How did they confirm flu?

The primary outcome was influenza A, diagnosed by medical doctors using a rapid influenza diagnostic test (RIDT) with a nasopharyngeal swab specimen, on an outpatient basis, following the manufacturer’s protocol. Other exclusionary assessments were used to limit false positives.

Drop outs

These were remarkably few, approx 50 in each original group number, and the most common reason was the three times a day supplementation requirement.

Simple 1 a day dosing and avoidance of pills will possibly facilitate better compliance.


Influenza A occurred in 18 of 167 (10.8%) children receiving vitamin D3 compared with 31 of 167 (18.6%) children receiving placebo (RR: 0.58; 95% CI; 0.34, 0.99; P = 0.04).

The incidences of influenza B and RIDT-negative influenza-like illness were not significantly different between the vitamin D3 and placebo groups. Asthma attacks occurred in 2 children receiving vitamin D3 compared with 12 children receiving placebo (RR: 0.17; 95% CI: 0.04, 0.73; P = 0.006) in children with a previous diagnosis of asthma. There were no significant differences in any other secondary outcomes between groups. There were no reports of adverse events in this study.

Other natural immune enhancing agents

A 10-d course of postexposure prophylaxis with zanamivir or oseltamivir resulted in only an 8% decrease in the incidence of symptomatic influenza in children.[2] In contrast, daily dietary probiotic supplementation was a safe effective way to reduce fever and other symptoms in small children.[3] Moreover, a significant preventive effect of a product containing echinacea, propolis, and vitamin C on the incidence of respiratory tract infections was observed in children.[4]

In conclusion, our study suggests that vitamin D3 supplementation  during the winter season may reduce the incidence of influenza A. This effect was prominent in specific subgroups of schoolchildren. Moreover, asthma attacks were also prevented by vitamin D3 supplementation.

How did it do this?

As discussed in this extensive review post, Vitamin D has antimicrobial and cytokine modulating effects as well as appearing to prevent viral adhesion and replication.


Mostly related to size of study group and lack of serum Vit D levels to try and define levels required for best defence. The compliance issues already noted might be well managed with a larger single dose of 2000iu in liquid form, this dose has already been shown to be safe taken for 12 months at a time in school children.[5]


Simple, cheap and safe – not an easy claim to make in pharmaceutical literature but one that can be made here. Vitamin D has demonstrated its versatility and the need for supplementation during the winter months or when sun exposure is limited to maintain the best chance of avoiding Influenza A as a school aged child. A greater than 70% gain in avoidance was achieved, mostly attained after 60 days supplementation. So start the supplementation strategy at least 30 days prior to the influenza season to provide best outcomes.


[1] Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, & Ida H (2010). Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. The American journal of clinical nutrition, 91 (5), 1255-60 PMID: 20219962

[2] Shun-Shin, M, Thompson, M, Heneghan, C, Perera, R, Harnden, A & Mant, D. Neuraminidase inhibitors for treatment and prophylaxis of influenza in children: systematic review and meta-analysis of randomised controlled trials. BMJ 2009;339:b3620. View Full Paper

[3] Leyer, GJ, Li, S, Mubasher, ME, Reifer, C & Ouwehand, AC. Probiotic effects on cold and influenza-like symptom incidence and duration in children. Pediatrics 2009;124:e172–9. View Full Paper

[4] Cohen, HA, Varsano, I, Kahan, E, Sarrell, EM & Uziel, Y. Effectiveness of an herbal preparation containing echinacea, propolis, and vitamin C in preventing respiratory tract infections in children: a randomized, double-blind, placebo-controlled, multicenter study. Arch Pediatr Adolesc Med 2004;158:217–21 View Full Paper

[5] Maalouf, J, Nabulsi, M, Vieth, R, et al.. Short- and long-term safety of weekly high-dose vitamin D3 supplementation in school children. J Clin Endocrinol Metab 2008;93:2693–701 View Full Paper

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