Natural compounds found in berries, tea and red wine are known to have protective properties that help regulate the immune system to fight infections.
Now, a new study shows that the flavonoids in these products works with a particular gut microbe to prevent severe flu infections.
In their tests on mice, scientists explained that this did not stop the highly contagious infection being contracted.
But the mechanism boosted the immune system and prevented the flu from harming the lung tissue.
The researchers said the findings could help explain why people have varied reactions to the infection.
Most people will feel better from influenza within a week but it can be dangerous for the elderly or people with certain illnesses.
Around the world, the World Health Organization estimates it causes 250,000 to 500,000 deaths annually.
‘For years, flavonoids have been thought to have protective properties that help regulate the immune system to fight infections,’ said first author Dr Ashley Steed, a pediatrician from St Louis Children’s Hospital in Missouri.
‘Flavonoids are common in our diets, so an important implication of our study is that it’s possible flavonoids work with gut microbes to protect us from flu and other viral infections. Obviously, we need to learn more, but our results are intriguing.’
Previous evidence suggests that the gut microbiome may be important in protecting against severe influenza infections.
The new research, carried out at Washington University School of Medicine in St Louis, aimed to identify the exact gut microbes that might provide that protection.
Additionally, nutritionists have long explored the potential health benefits of flavonoids.
They discovered that the microbe clostridium orbiscindens was protective.
They believe it interacts with the dietary compounds to boost interferon, which are proteins produced by the body’s cells as a defensive response to viruses.
The metabolite that triggered the reaction is called desaminotyrosine, otherwise known as DAT.
‘It’s not only having a diet rich in flavonoids, our results show you also need the right microbes in the intestine to use those flavonoids to control the immune response,’ said another of the study’s authors, Dr Thaddeus Stappenbeck.
‘This prevented influenza-related lung damage in the mice. It is this kind of damage that often causes significant complications such as pneumonia in people.’
Dr Steed added: ‘When we gave DAT to mice and then infected them with influenza, the mice experienced far less lung damage than mice not treated with DAT.
Although the lungs of DAT-treated mice didn’t have as much flu damage, their levels of viral infection were identical to those in mice that didn’t get the treatment.
‘The infections were basically the same,’ Dr Stappenbeck said.
‘The microbes and DAT didn’t prevent the flu infection itself; the mice still had the virus. But the DAT kept the immune system from harming the lung tissue.’
The findings are important because annual flu vaccines are not always effective at preventing infections, say the researchers.
‘With DAT, it may be possible to keep people from getting quite as sick if they do become infected,’ said Dr Steed.
‘This strategy doesn’t target the virus. Instead, it targets the immune response to the virus.
‘That could be valuable because there are challenges with therapies and vaccines that target the virus due to changes in the influenza virus that occur over time.’
The study was published in the journal Science.