There could be a link between coronavirus death rates and eating certain vegetables, according to a preliminary study in Europe.
It suggested that increasing the average consumption of cabbage or cucumber by 1 gram a day could reduce a country’s mortality rate by 13.6 per cent or 15.7 per cent, respectively.
But lettuce could potentially have the opposite effect, while other vegetables did not show any expected disease-fighting benefits, according to the researchers led by Jean Bousquet, a professor of pulmonary medicine at Montpellier University in France.
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The study, which has not been peer-reviewed, was limited to Europe, and the researchers cautioned that the results could have been affected by uncertainties such as deaths being counted differently in some countries, but it was the “first attempt to link death rates with food consumption”.
“Nutrition should not be overlooked” as a factor behind Covid-19 deaths, said Bousquet, former chairman of the WHO Global Alliance against Chronic Respiratory Diseases, and colleagues in the paper posted on preprint server medRxiv.org on Saturday.
They noted that Belgium, Britain, Spain, Italy, Sweden and France have recorded the highest Covid-19 death rates in the world. More than 800 have died per million people in Belgium, for instance, a rate twice that of the United States, the country worst-hit by the pandemic.
In these countries, the factors that could affect mortality such as the enforcement of lockdown measures and climate varied, but they had one thing in common: cabbage and cucumber are not a big part of the diet.
In France, the average person was found to consume about 1 gram (0.04oz) of cabbage a day, while in the other five countries, the average was less than 5 grams (0.18oz) a day.
In contrast, nearly 30 grams (1.1oz) of cabbage was consumed per day on average in Latvia, where the death rate from Covid-19 is among the world’s lowest, at 16 per million people.
The researchers found a similar pattern in cucumber consumption. Cypriots did not eat much cabbage, but more than 30 grams of cucumber was consumed on average per day – and the death rate in Cyprus was on par with Latvia’s.
This could be to do with a protein in humans called Nrf2. Sars-Cov-2, the virus that causes the Covid-19 disease, can cause serious inflammation in severely ill patients, including generating damaging oxygen particles. Nrf2 can bind with these particles to reduce their harm – and that is where cabbage and cucumber come in.
Previous studies have suggested the vegetables have natural compounds – curcumin, sulforaphane and vitamin D – that can boost the production of Nrf2.
According to the European researchers, that may mean people with more cucumber and cabbage in their diets could be better prepared to fight the virus.
But the theory did not extend to other vegetables known to increase production of Nrf2. Broccoli and cauliflower, for instance, were not found to have any benefits.
The researchers said one possible explanation was the relatively low daily intake of these vegetables. The average consumption for both broccoli and cauliflower is under 6 grams (0.21oz) a day across Europe, which could be “too low to provide any protection”, they said.
Lettuce was another puzzle, and one the researchers had no explanation for yet. They found countries where more lettuce was eaten like Spain and Italy had considerably higher Covid-19 death rates than those where it was eaten less, such as Germany. The difference was not statistically significant for some countries, but the pattern was clear even after adjusting for factors such as GDP, population density, obesity prevalence and age distribution.
Ren Guofeng, an associate professor of medical nutrition at Central South University in Changsha, said there was strong evidence that vegetable consumption could affect the outcomes of many chronic diseases.
But he noted that much was still unknown about the new coronavirus, and there could be unexpected factors at play. “It would help the battle against the pandemic if we could find a secret key in the diet, but so far the evidence is not strong enough to support this theory,” he said.
An epidemiologist with the Pasteur Institute in Shanghai who requested anonymity said the study had limitations and noted it had yet to be peer-reviewed. She said the results should be treated with caution, and people should “use scientific common sense to make a judgment”.
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