He proposed that the cause of influenza epidemics during winter may be connected to seasonal fluctuations of vitamin D, which is produced in the skin under the influence of solar (or artificial) UV radiation.
Han foreslog at influenzaepidemier i vintermånederne kunne hænge sammen med årstidsændringen af D-vitamin-niveauet, som dannes i huden via UV-lys fra solstråler.