Influenza, solar radiation and vitamin D

Abstract

The annual death numbers of influenza and pneumonia in Norway were studied for the time period 1980 - 2000. No direct relationships were found with the variations of the annual UVB fluences, probably due to the fact that these variations did not exceed 30 %. However, there was a very pronounced seasonal variation of both influenza deaths and pneumonia deaths, the vast majority occurring during the winter. Vitamin D levels were also estimated from several publications. The data support the hypothesis that a high vitamin D level, as that found in the summer, acts in a protective manner with respect to influenza as well as pneumonia. The findings are discussed and compared with data from tropical and subtropical areas.

Acknowledgements

We want to thank Øystein Kravdal from the Institute of Economy (Oslo University, Norway) for calculating the number of deaths of influenza and pneumonia. Direct overpass TOMS data were provided by NASA/GSFC.

Figures and Tables

Figure 1 Seasonal variations of serum levels of vitamin D (▼) in the Nordic countries, given as averages from three reports in ref. 9. Photosynthesis of vitamin D for Southern Norway (■) is calculated by use of the action spectrum in ref. 7, UV measurements in Oslo and radiative transfer calculations using a cylinder model as described in the text. The results are presented in relative units (rel. u.). Influenza deaths in two periods (●, ◯) in Norway are also given.

Figure 2 Upper: The UVB levels in Norway in the period 1980–2000.29 In this case the UVB fluences were determined for a horizontal plane with the CIE erythema spectrum, which is UVB weighted and very close to the vitamin D spectrum used in the rest of this work. Lower: The average number of influenza and pneumonia deaths per year in Norway in the same period.