Vitamin D supplements could spare more than three million people from colds or flu in the UK each year, researchers claim. The sunshine vitamin is vital for healthy bones, but also has a role in the immune system. The analysis, published in the British Medical Journal, argues food should be fortified with the vitamin. The immune system uses vitamin D to make antimicrobial weapons that puncture holes in bacteria and viruses. But as vitamin D is made in the skin while out in the sun, many people have low levels during winter. The researchers pooled data on 11,321 people from 25 separate trials to try to get a definitive answer. The team at Queen Mary University of London (QMUL) looked at respiratory tract infections - which covers a wide range of illnesses from a sniffle to flu to pneumonia. Overall, the study said one person would be spared infection for every 33 taking vitamin D supplements. That is more effective than flu vaccination, which needs to treat 40 to prevent one case. There were greater benefits for those taking pills daily or weekly - rather than in monthly super-doses - and in people who were deficient in the first place. One of the researchers, Prof Adrian Martineau, said: "Assuming a UK population of 65 million, and that 70% have at least one acute respiratory infection each year, then daily or weekly vitamin D supplements will mean 3.25 million fewer people would get at least one acute respiratory infection a year."