Study links fermented vegetable consumption to low COVID-19 mortality

By Sally Robertson, B.Sc.Reviewed by Danielle Ellis, B.Sc.Jul 8 2020

An intriguing new study by researchers in Europe suggests that coronavirus disease 2019 (COVID-19) mortality rates are likely to be lower in countries where diets are rich in fermented vegetables.

Study: Association between consumption of fermented vegetables and COVID-19 mortality at a country level in Europe. Image Credit: Foxys Forest Manufacture / Shutterstock

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

Earlier this year, Jean Bousquet (Charité, Universitätsmedizin Berlin) and colleagues investigated whether diet may contribute to the significant variation in COVID-19 death rates that have been observed between countries. The study found that in some countries with low mortality rates, the consumption of traditional fermented foods was high.

Now referring to the current study, “the negative ecological association between COVID-19 mortality and consumption of fermented vegetables supports the hypothesis previously reported,” writes the team.

The researchers say that if their hypothesis is confirmed in future studies, COVID-19 will be the first infectious disease epidemic to involve biological mechanisms that are associated with a loss of “nature.”

Significant changes in the microbiome caused by modern life and less fermented food consumption may have increased the spread or severity of the disease, they say.

A pre-print version of the paper is available on the server medRxiv*, while the article undergoes peer review. However, this paper is a preliminary report and should not be regarded as conclusive or established information.

COVID-19 death rate and consumption of foods in European Union countries

Unexplained geographical variation in COVID-19 mortality

Since the COVID-19 outbreak began in Wuhan, China, late last year, it has exhibited significant and unexplained geographical variations in the number of people infected and mortality rates.

In Europe, the death rate in Italy, France, and the UK, for example, has been very high, compared with the Balkans and some Nordic countries. Similar disparities have also been observed across the globe.

Although aspects such as age structure, the timing of interventions, employment type, and housing conditions are likely to be the most relevant factors, other potentially relevant factors such as nutrition should not be overlooked, say Bousquet and colleagues.  

The potential role nutrition may play

Many foods have antioxidative properties, and nutrition has been proposed to play a mitigating role in COVID-19. The fermentation process increases the antioxidant activity of food products, including milk, fruit, vegetables, and meat.

Bousquet and team hypothesized that the consumption of fermented foods might explain some of the differences in COVID-19 mortality rates between countries in Europe.

To test the hypothesis, the team used information from the European Food Safety Authority (EFSA) Comprehensive European Food Consumption Database to assess the consumption of different fermented foods by country, including vegetables, milk, yogurt, sour milk, and pickled/marinated vegetables.

COVID-19 mortality rates were calculated using information from the Johns Hopkins Coronavirus Resource Center, and EuroStat was used to obtain data on confounders by country, including gross domestic product, population density, the proportion aged over 64 years, unemployment rate and obesity prevalence.

What did the study find?

The researchers report that of all the variables considered, only fermented vegetables had a significant impact on the mortality rate by country.

For each gram per day increase in the average national consumption of fermented vegetables, the risk for COVID-19 mortality fell by 35.4%.

“Although this study is only indicative of the role of diet in COVID-19, it is, however, another piece of the hypothesis proposing that traditional fermented foods may be involved in the prevention of severe COVID-19 at a country level,” writes the team.

What about regions outside of Europe?

The researchers point out that their study was restricted to European countries and that it would be useful to test the hypothesis in other regions where fermented food consumption is high, and COVID-19 mortality rates are low.

In Asia, for example, death rates are very low, and the pandemic appears to be under control, say Bousquet and team. “The same happened in Africa where the COVID-19 spread was predicted to be catastrophic, and death rates appear to be low,” they write.

The authors say it would be of great value to use food consumption data from such countries to perform definitive epidemiologic and mechanistic studies to confirm the current findings.

A “loss of nature” may be involved

“If the hypothesis is proved, COVID-19 will be the first infectious disease epidemic whose biological mechanisms are proved to be associated with a loss of nature,’” writes the team.

“When modern life led to eating reduced amounts of fermented foods, the microbiome drastically changed, and this may have facilitated SARS-CoV-2 to spread or to be more severe.”

The hypothesis requires testing in individual studies conducted in countries where there is widespread high consumption of fermented vegetables, concludes the team.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources