Autumn COVID-19 surge dates in Europe correlated to latitudes, not to temperature-humidity, pointing to vitamin D as contributing factor
Walrand,
Autumn COVID-19 surge dates in Europe correlated to latitudes, not to temperature-humidity, pointing to..,
, S., Nature, doi:10.1038/s41598-021-81419-w
Analysis of the increase in COVID-19 cases in European countries, showing no correlation with temperature, but a significant correlation with country latitude. Since UV radiation decreases earlier for higher latitudes, this supports the theory that low vitamin D levels increases COVID-19 risk.
Author recommends that vitamin D supplementation be considered to reduce pandemic severity during the winter, noting that UV levels in Europe and Northern USA will not return to a level above that of October until the end of March.
Walrand et al., 21 Jan 2021, peer-reviewed, 1 author.
Abstract: www.nature.com/scientificreports
OPEN
Autumn COVID‑19 surge dates
in Europe correlated to latitudes,
not to temperature‑humidity,
pointing to vitamin D
as contributing factor
Stephan Walrand
To determine the factor triggering the sudden surge of daily new COVID-19 cases arising in most
European countries during the autumn of 2020. The dates of the surge were determined using a fitting
of the two last months of reported daily new cases in 18 European countries with latitude ranging from
39° to 62°. The study proves no correlation between the country surge date and the 2 weeks preceding
temperature or humidity but shows an impressive linear correlation with latitude. The country surge
date corresponds to the time when its sun UV daily dose drops below ≈ 34% of that of 0° latitude.
Introducing reported seasonal blood 25-hydroxyvitamin D (25(OH)D) concentration variation into the
reported link between acute respiratory tract infection risk and 25(OH)D concentration quantitatively
explains the surge dynamics. Several studies have already substantiated a 25(OH)D concentration
impact on COVID-19 severity. However, by comparing different patient populations, discriminating
whether a low 25(OH)D concentration is a real factor underlying COVID-19 severity or only a marker
of another weakness that is the primary severity factor can be challenging. The date of the surge is
an intrapopulation observation and has the benefit of being triggered only by a parameter globally
affecting the population, i.e. decreases in the sun UV daily dose. The results indicate that a low 25(OH)
D concentration is a contributing factor to COVID-19 severity, which, combined with previous studies,
provides a convincing set of evidence.
Most European countries underwent an unexpected surge of daily new COVID-19 cases in autumn (Fig. 1),
imposing new confinement rules and emergency lockdowns.
A commonly reported explanation is the decreasing temperature. The aim of this study is to challenge this
assumption against a pure latitude impact.
Materials and methods
Data sources. The countries’ daily new COVID-19 cases, more exactly, the daily new SARS-CoV-2 seropositive cases, were obtained from the European Union agency European Centre for Disease Prevention and
Control
(https://www.ecdc.europa.eu/en/publications-data/download-todays-data-geographic-distributioncovid-19-cases-worldwide).
The country population weighted centre (PWC) latitudes were obtained from the Baylor University population resource (http://cs.ecs.baylor.edu/~hamerly/software/europe_population_weighted_centers.txt).
The averaged 2-week temperatures and humidity preceding the surge dates were computed from https://rp5.
ru, which collects the archives of all airport weather stations in the world. For each country, an airport close
to the PWC was chosen (see supplementary Excel file). The average temperature and humidity were computed
between 8h00 to 20h00, outside this period, the population is mostly indoors.
School opening dates of 15 out of the 18 countries studied were found at https://eacea.ec.europa.eu/natio
nal-policies/eurydice/sites/eurydice/files/school_calendar_2020_21_0.pdf.
The theoretical sun UVB daily dose for vitamin D production, as a function of latitude and of the day of the
year, was derived from the digitalization of Fig. 1B from reference1.
Cliniques Universitaires Saint-Luc, 1200 Brussels, Belgium. email: stephan.walrand@uclouvain.be
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