Introduction
A COVID-19 epidemic started in China and then disseminated to other
Asian countries before becoming a pandemic. There is a large variability
across countries in both incidence and mortality, and most of the
current debates on COVID-19 focus on the differences between countries.
German fatalities are strikingly low as compared to many European
countries. Among the several explanations proposed, an early and large
testing of the population was put forward 1 as well as
social distancing. However, little attention has been given to regional
within-country differences that may propose new hypotheses.
It would appear that the pandemic has so far resulted in proportionately
fewer deaths in some Central European countries, the Balkans, China, in
most Eastern Asian countries as well as in many Sub-Saharan African
countries. Several reasons can explain this picture. One of them may be
the type of diet in these low mortality countries. 2
Diet has been proposed to mitigate COVID-19. 3 Some
foods or supplements may have a benefit on the immune response to
respiratory viruses. However, to date, there are no specific data
available to confirm the putative benefits of diet supplementation,
probiotics, and nutraceuticals in the current COVID-19 pandemic.4 News and social media platforms have implicated
dietary supplements in the treatment and prevention of COVID-19 without
evidence. 5
In this paper, we discuss country and regional differences in COVID-19
deaths. We attempt to find potential links between foods and differences
at the national or regional levels in the aim to propose a common
mechanism focusing on oxidative stress that may be relevant in COVID-19
mitigation strategies. We used cabbage and fermented vegetable as a
proof-of-concept.
Biases to be considered
According to the Johns Hopkins coronavirus resource center
(https://coronavirus.jhu.edu ), one of the most important ways of
measuring the burden of COVID-19 is mortality. However, death rates are
assessed differently between countries and there are many biases that
are almost impossible to assess. Using the rates of COVID-19 confirmed
cases is subject to limitations that are similar to or even worse than
the differences in the use of COVID-19 testing.
Differences in the mortality rates depend on health care systems, the
reporting method and many unknown factors. Countries throughout the
world have reported very different case fatality ratios - the number of
deaths divided by the number of confirmed cases - but these numbers
cannot be compared easily due to biases. On the other hand, for many
countries, the methodology used to report death rates in the different
regions is standardized across the country.
We used mortality per number of inhabitants to assess death rates, as
proposed by the European Center for Disease Prevention and Control
(ecdc, https://www.ecdc.europa.eu/en), and to report trends with cutoffs
at 25, 50, 100 and 250 per million.
Our hypothesis is mostly based on ecological data that are
hypothesis-generating and that require confirmation by proper studies.