Vitamin D3 and Flu Prevention

There has been rising interest in the past few years about Vitamin D’s potential for preventing/controlling flu and other respiratory illnesses.
One notable advocate for Vitamin D as a preventative against flu is Dr. John Cannell, lead author of a 2008 review article in the journal Virology. Cannell and his co-authors build on a decades-old insight from a British researcher, Hope-Simpson, who speculated that influenza was seasonal because of a co-factor related to sun exposure. The co-factor, this article asserts, is Vitamin D and its positive effects on immunity.

The second paragraph quoted below (from the same 2008 article in Virology) reports rather dramatic evidence that African-Americans, who are especially prone to Vitamin D deficiency, might very substantially decrease their susceptibility to colds and flu by supplementing with 2000IU daily during winter months.

Vitamin D, innate immunity, and influenza

Hope-Simpson’s model theorized that an unidentified “seasonal stimulus,” inextricably bound to solar radiation, substantially controlled the seasonality of influenza. Recent evidence suggests the “seasonal stimulus” may be seasonal impairments of the antimicrobial peptide (AMPs) systems crucial to innate immunity, impairments caused by dramatic seasonal fluctuations in 25-hydroxy-vitamin D [25(OH)D] levels. The evidence that vitamin D has profound effects on innate immunity is rapidly growing.

In fact, Aloia and Li-Ng presented evidence of a dramatic vitamin D preventative effect from a randomized controlled trial (RCT). In a post-hoc analysis of the side effect questions of their original three-year RCT, they discovered 104 post-menopausal African American women given vitamin D were three times less likely to report cold and flu symptoms than 104 placebo controls. A low dose (800 IU/day) not only reduced reported incidence, it abolished the seasonality of reported colds and flu. A higher dose (2000 IU/day), given during the last year of their trial, virtually eradicated all reports of colds or flu. Recent discoveries about vitamin D’s mechanism of action in combating infections led Science News to suggest that vitamin D is the “antibiotic vitamin” due primarily to its robust effects on innate immunity.


Cannell, John J, Michael Zasloff, Cedric F Garland, Robert Scragg and Edward Giovannucci. On the epidemiology of influenza. Virology Journal 2008, 5:29. We accessed this 11/10/2009 at

Aloia J F, Li-Ng M: Epidemic influenza and vitamin D. Epidemiol Infect 2007; 135: 1095–1096.

See the NYBC entry Vitamin D3 2500IU for additional information. This format of D3 is a convenient way to supplement at approximately the levels discussed by Cannell and others. (NYBC also stocks D3 1000IU and D3 400IU formats.)