Vitamin D for flu protection

Posted on Tue, 11 Aug 09

As early as the 1940s it was found that when mice received low levels of vitamin D they were more susceptible to experimental swine flu infection than mice receiving adequate vitamin D [1].  Fast track to 2009 and scientists from the Public Health Agency of Canada are racing to discover whether vitamin D may be a way to fight the influenza epidemic, and with good reason [2].  There is mounting evidence to show that vitamin D may be a simple and safe solution to reducing influenza risk.

Flu pandemic or wide-spread D-ficiency?  

Vitamin D, which is manufactured by skin in response to sunlight, may explain why influenza is typically worse in the darker months of winter, and perhaps why flu pandemic death rates are higher during winter months [3].  Vitamin D deficiency is at its peak during winter however deficiency is also common in summer, in fact vitamin D deficiency is very common in countries with high levels of sunlight such as Australia, Turkey and India [4].  

It has been estimated that regardless whether you are a child or adult, living in Australia, America, Asia or Europe you are at a high risk for vitamin D deficiency,  an alarming 1 out of every 2 people have low vitamin D levels [5].  Vitamin D deficiency is a pandemic health problem.

Vitamin D protects against infection

The ability of your immune system to fight infection is strongly dependant on vitamin D, with low levels of vitamin D resulting in a poor immune response [6]. Specifically vitamin D protects against respiratory infection by dramatically stimulating the disease fighting potential of white blood cells such as the neutrophils and macrophages that line your lungs as a defensive barrier [7].

Increase your D-fence against flu

Studies have shown that vitamin D deficiency predisposes to respiratory viral infections and that increasing vitamin D level reduces risk [7]. One study reported that women taking 2000IU per day of vitamin D for one year virtually eliminated symptoms of colds and flu [8].

It is difficult to obtain adequate vitamin D from dietary sources and health recommendations to reduce sun exposure have resulted in wide-spread vitamin D deficiency even in countries with adequate sunlight.

Currently experts recommend that children and adults take 800-1000 IU of vitamin D a day [5]. It is advisable to start vitamin D supplements before winter sets in as it may take a number of months to raise levels close to an optimum. Considering the prevalence of vitamin D deficiency it is also advisable to have your blood levels assessed as you may need higher levels of vitamin D to correct the problem.

Image: A close-up of a virus

References

1. YOUNG GA Jr, UNDERDAHL NR, CARPENTER LE. Vitamin D intake and susceptibility of mice to experimental swine influenza virus infection. Proc Soc Exp Biol Med. 1949 Dec;72(3):695-7

2. Martin Mittelstaedt. Health agency to test link between flu, vitamin D. The Globe and Mail. Tuesday, Jul. 28, 2009.

3. Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, Madronich S, Garland CF, Giovannucci E. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec;134(6):1129-40.

4. Holick MF. Vitamin D deficiency. N Engl J Med. 2007 Jul 19;357(3):266-81.

5. Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr. 2008 Apr;87(4):1080S-6S

6. Liu, P. et al.  Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science. 2006  311:1770-1773.

7. Canell J et al. Epidemic influenza and vitamin D. Epidemiol. Infect. (2006), 134, 1129–1140.

8. Aloia JF, Li-Ng M. Re: epidemic influenza and vitamin D. Epidemiol Infect. 2007 Oct;135(7):1095-6; author reply 1097-8.