Vitamin D is always in the news. Nearly one in three Brits is ­deficient in vitamin D mainly due to diet, our weather and the fact that as a nation we prefer to stay indoors rather than go out.

During the spring and summer the skin makes vitamin D when it’s exposed to the sun.

But in the autumn and winter most people have to rely on their diet to get enough. They can do that by eating liver, eggs, red meat and plenty of oily fish – but the millions who don’t eat enough of these foods should probably take supplements.

Vitamin D has many health giving benefits and here’s a new one – it protects against colds and flu.

Fortifying food with vitamin D would stop 3.25 million people a year suffering chronic colds and flu.

A new UK study claims taking vitamin D at least once a week slashes the risk by 50% of some people falling ill with a respiratory infection.

Chronic respiratory infections are responsible for a quarter of GP appointments in Britain. Every year, 70% of the UK population suffers with at least one bout of flu, coughs or colds, causing 300,000 hospital ­admissions and 35,000 deaths.

If every Brit ate vitamin-fortified food, illness levels would be slashed.

The researchers from Queen Mary University of London feel it is ­unrealistic to expect everyone to take supplements so they want vitamin D to be added to foods such as milk or bread as in the US, Canada, Sweden, Finland and Australia.

The British Medical Journal study analyses data from nearly 11,000 people who took part in 25 clinical trials conducted in 14 countries. Among people who are deficient in vitamin D, taking supplements reduces the risk of respiratory infection by 50%, and among others the risk drops by up to 20%.

Lead researcher Professor Adrian Martineau said: “This collaborative research effort has yielded the first definitive evidence that vitamin D really does protect against respiratory infections. Our data has provided a whole new reason to back up the advice on vitamin D supplementation.”

But he says it isn’t realistic to expect everyone to take pills.

“Either the whole adult population takes an over-the-counter supplement or moves are made to introduce food fortification”.

His team now plans to directly study the benefits of food fortification.

A Department of Health spokesman said the Government would remain open to considering the results of studies, adding: “Mandatory food ­fortification is a complex issue, but experts keep evidence under review.”