InfluenzaExposure to sunlight

The best evidence that solar UVB irradiance, through vitamin D production, reduces the risk of influenza is its seasonality.

The best evidence that solar UVB irradiance, through vitamin D production, reduces the risk of influenza is its seasonality1.  Even the recent A/H1N1 “swine flu” epidemic, which started in Mexico in April, had peak incidence rates in winter2.  

However, variations in absolute humidity levels also contribute to the seasonality since the influenza virus lives longer outside a human or animal body at low humidity levels34.  Absolute humidity levels are lowest in winter due to low temperatures.  While the annual variation of solar radiation doses has two effects on risk of influenza, it is much easier to control serum 25(OH)D levels. 

Page last edited: 06 May 2011

References

  1. Cannell, J. J. Vieth, R. Umhau, J. C. Holick, M. F. Grant, W. B. Madronich, S. Garland, C. F. Giovannucci, E. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec; 134 (6): 1129-40.
  2. Ross, T. et al Seroprevalence Following the Second Wave of Pandemic 2009 H1N1 Influenza. PLoS Curr Influenza. 2010, Feb; 24
  3. Shaman, J. Kohn, M. Absolute humidity modulates influenza survival, transmission, and seasonality. Proc Natl Acad Sci U S A. 2009 Mar 3; 106 (9): 3243-8.
  4. Shaman, J. Pitzer, V. Viboud, C. Lipsitch, M. Grenfell, B. Absolute humidity and the seasonal onset of influenza in the continental US. PLoS Curr Influenza. 2009 Dec; 18RRN1138.