Drink black tea and red wine to limit flu symptoms, researchers say

A compound found in foods such as black tea, red wine and blueberries can prevent severe flu infections in mice, according to new research published in the journal Science.

The research, by the Washington University School of Medicine, also indicates that consuming the plant flavonoids before flu develops will limit its impact. The work could explain the wide variation in human responses to influenza infection.

Previous research suggested that the gut microbiome may be important in protecting against severe influenza infections. In this study, the researchers aimed to identify which gut microbes might provide that protection.

The researchers screened human gut microbes looking for one that metabolised flavonoids. They identified one such microbe that they suspect might protect against flu damage. The microbe – clostridium orbiscindens – degrades flavonoids to produce a metabolite that enhances interferon signalling.

The study’s first author, Ashley Steed, said: ‘For years, flavonoids have been thought to have protective properties that help regulate the immune system to fight infections. 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.’

The study’s senior author, Thaddeus Stappenbeck, said: ‘The metabolite is called desaminotyrosine, otherwise known as DAT. 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.’

‘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. We were able to identify at least one type of bacteria that uses these dietary compounds to boost interferon, a signaling molecule that aids the immune response. 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.’

Although the lungs of DAT-treated mice didn’t have as much flu damage, their levels of viral infection were identical. ‘The infections were basically the same. 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,’ Stappenbeck said.

The researchers say they will now try to identify other gut microbes that also may use flavonoids to influence the immune system, as well as exploring ways to boost the levels of those bacteria in people whose intestines aren’t adequately colonised with those microbes.