Epidemic influenza and vitamin D

Abstract

In 1981, R. Edgar Hope-Simpson proposed that a 'seasonal stimulus' intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH)2D, a steroid hormone, has profound effects on human immunity. 1,25(OH)2D acts as an immune system modulator, preventing excessive expression of inflammatory cytokines and increasing the 'oxidative burst' potential of macrophages. Perhaps most importantly, it dramatically stimulates the expression of potent anti-microbial peptides, which exist in neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection. Volunteers inoculated with live attenuated influenza virus are more likely to develop fever and serological evidence of an immune response in the winter. Vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children. We conclude that vitamin D, or lack of it, may be Hope-Simpson's 'seasonal stimulus'.

Unexpected actions of vitamin D: new perspectives on the regulation of innate and adaptive immunity

“…71 In other studies, a role for 25OHD in counteracting infection in the upper respiratory tract has been proposed. 72,73 These observations were based in part on epidemiological data linking seasonal variations in vitamin D status with the seasonality of infections such as influenza, 72 as well as randomized clinical studies demonstrating protective effects of vitamin D supplementation against colds and influenza. 73 Unlike the model described for tuberculosis, a mechanism by which vitamin D can combat respiratory infection due to colds or influenza has yet to be proposed; however, in view of the fact that cathelicidin has been shown to exhibit antiviral properties, 74 it is exciting to speculate that vitamin D therapy may provide a novel strategy for preventing these prevalent clinical problems.…”

An estimate of the global reduction in mortality rates through doubling vitamin D levels

“…Cannell et al (2006) hypothesized that epidemic influenza is largely seasonal because of the annual cycle of solar UVB and vitamin D production. Two RCTs have supported this hypothesis (Urashima et al, 2010 and references therein).…”

“…Papers outlining the evidence for vitamin D in reducing the burden of diseases with the highest mortality rates for which vitamin D reduces incidence and mortality rates include those for CVD (Parker et al, 2010), cancer , bacterial and viral respiratory infections (Cannell et al, 2006;Liu et al, 2007), chronic obstructive pulmonary disease (COPD; Black and Scragg, 2005), tuberculosis (TB; Liu et al, 2007), diabetes (Parker et al, 2010;Pittas et al, 2010), musculoskeletal diseases leading to falls (Cauley et al, 2008;Pfeifer et al, 2009) and dementia (Grant, 2009a).…”

A longitudinal ecological study of seasonal influenza deaths in relation to climate conditions in the United States from 1999 through 2011

“…It was also suggested that solar radiation degrades influenza virus [1]. Finally, it was also described that solar radiation triggers robust seasonal vitamin D production in the skin, and because of vitamin D’s known anti-infective/immune modulating properties, the consequence of vitamin D deficiency in winter months may mediate increased seasonal influenza epidemics [17]. …”