Now there is another good reason to urge your teenagers to eat up their fruit, vegetables and oily fish. Doing so could, according to researchers from the Harvard School of Public Health, make them less prone to asthma, coughing, wheezing and generally “underperforming” lungs.

But it’s not only youngsters who can benefit. Other work, published recently in the journal Thorax, also revealed that eating a Mediterranean-style diet (which is naturally rich in these foods) has a protective effect on the lung health of men – which suggests that we should all be trying to double our current woeful average of 2.5 servings of fruit and veg a day.

Scientists have yet to discover the exact mechanisms to explain why fruit, vegetables and oily fish manage to have lung-protecting effects, but they have a few ideas about what may well be going on.

Take asthma. This is often triggered when we breathe in irritants in air pollution and tobacco smoke. In an asthma attack the bronchioles (tiny airways in the lungs) constrict, triggering the release of histamine and other chemicals that, in turn, cause inflammation, swelling and the production of extra mucus, making it hard to breathe.

Vitamin C, found in large amounts in many fruits and in vegetables such as peppers, broccoli, peas and even potatoes, is a major antioxidant that should be present in good amounts in the lining of our respiratory tracts. It should spring into action immediately when we breathe in oxidants in smoke and car fumes, helping to disarm them and make an attack less likely. If this vitamin C is lacking in our diets, there may be too little of it in our airways to tackle asthma-causing pollutants.

But the protective effects of fruits and vegetables are unlikely to be down to vitamin C alone. Fruit such as apples, raspberries, bananas and apricots, as well as onions and tomatoes, are good for quercetin. Like vitamin C, quercetin has strong antioxidant properties – but it is also believed to prevent the release of histamine, thus potentially helping to stop inflammation and swelling of airways and the production of excess mucus.

Onions have another potential winning property when it comes to easy breathing. They give us sulphur-based compounds, also found in garlic, shallots, chives and spring onions, which seem to have a mild antibiotic action, helping our bronchioles to relax.

In the Harvard study on teenagers, the researchers also linked lower intakes of vitamin E – found particularly in dark green leafy vegetables – with a greater likelihood of asthma.

Given that “greens” are one of the least popular vegetables for children and teenagers, it is good to know that sweet potatoes are also packed with this vitamin, while blackberries, almonds and sunflower oil also provide it.

As for oily fish, think salmon, mackerel, anchovies, sardines and eel. Their potential lung-protecting properties can be traced to the antiinflammatory effects of their omega3 oils.

If you find oily fish hard to stomach, try putting salmon in fishcakes or putting anchovies on pizzas.

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