We find that sunlight strongly protects against getting influenza: A 10% increase in relative sunlight decreases the influenza index in September or October by 1.1 points on a 10-point scale

Sunlight and Protection Against Influenza. David J.G. Slusky, Richard J. Zeckhauser. Economics & Human Biology, November 14 2020, 100942. https://doi.org/10.1016/j.ehb.2020.100942

Rolf Degen's take: https://twitter.com/DegenRolf/status/1327622311172837376

Highlights

• Medical literature suggests vitamin D protects against respiratory infections.

• Humans exposed to sunlight produce vitamin D directly.

• A 10% increase in relative sunlight decreases fall influenza by 1.1 out of 10.

• This relationship is driven by almost entirely by the H1N1 epidemic in fall 2009.

Abstract: Recent medical literature suggests that vitamin D supplementation protects against acute respiratory tract infection. Humans exposed to sunlight produce vitamin D directly. This paper investigates how differences in sunlight, as measured over several years across states and during the same calendar week, affect influenza incidence. We find that sunlight strongly protects against getting influenza. This relationship is driven almost entirely by the severe H1N1 epidemic in fall 2009. A 10% increase in relative sunlight decreases the influenza index in September or October by 1.1 points on a 10-point scale. A second, complementary study employs a separate data set to study flu incidence in counties in New York State. The results are strongly in accord.

JEL codes: I10I12I18Q5N32

Keywords: Seasonal InfluenzaSunlightVitamin DNatural ExperimentH1N1