People with lung infections are being encouraged to keep eating vegetables such as Brussels sprouts and cabbage in a bid to ease their illness.

Scientists said that cruciferous vegetables, which include broccoli, Brussels sprouts, cabbage, cauliflower, horseradish and turnips, contain a molecule which helps to maintain a healthy “barrier” in the lung which may in turn ease lung infections.

Researchers from the Francis Crick Institute examined a protein called the aryl hydrocarbon receptor (AHR), which can be activated by natural molecules in this type of vegetable.

The effect AHR has on immune cells is well understood but now scientists have found that it also plays a role in endothelial cells lining blood vessels in the lung.

The lung has a barrier made up of two layers, one of endothelial cells and one of epithelial cells, which allow oxygen to enter. But the barrier has to be kept strong to ward off pollution, viruses and bacteria.

The research team from the Crick conducted a series of experiments on mice which found that AHR plays an important role in helping maintain a strong barrier.

Mice with flu were found to have blood in air spaces between their lungs because it had leaked across a damaged barrier.

But AHR appeared to stop the barrier from leaking as much. They found that when AHR was “overactivated” there was less blood in lung spaces.

The scientists also found that mice with enhanced AHR activity did not lose as much weight when infected with flu, and were able to better fight off a bacterial infection on top of the original virus.

When AHR was prevented from being expressed in lung endothelial cells of mice, there was greater damage to the barrier, according to the study published in the journal Nature.

Meanwhile, infected mice did not eat as much food when ill so their intake of foods which activated AHR was reduced, which appeared to lead to more lung damage.

Mice on a diet rich with cruciferous vegetables were found to have healthier lung barriers and suffered less lung damage when infected with flu.

Andreas Wack, group leader of the Immunoregulation Laboratory at the Crick, said: “Until recently, we’ve mainly looked at barrier protection through the lens of immune cells.

“Now we’ve shown that AHR is important for maintaining a strong barrier in the lungs through the endothelial cell layer, which is disrupted during infection.

“People may be less likely to maintain a good diet when they’re ill, so aren’t taking in the molecules from vegetables which make this system work. It’s a good idea to eat lots of cruciferous vegetables anyway, but this shows it’s even more important to continue eating them when you’re ill.”

Commenting on the study, Dr John Tregoning, reader in respiratory infections at Imperial College London, said: “This study is important because it shows how the cells that line the lungs protect against damage following viral infection and that protection from infectious disease is not the sole reserve of the immune system.

“The study shows that a compound derived from broccoli (and other cruciferous vegetables) can improve protection against viral lung damage.

“The study is well performed and the conclusions in the mouse model are well backed up.

“How this study translates into people during lung infection needs further work.”