But in what is being hailed a “major step forward”, the new research now shows the vitamin also plays a significant role in preventing everyday illness.
Published in the British Medical Journal, the study explains how researchers examined data from almost 11,000 participants from all over the world about the effect of vitamin D on acute respiratory illnesses, which can include earache, bronchitis, pneumonia and the common cold.
The group of infections account for around 300,000 hospital admissions each year.
The analysis showed that regular supplements resulted in a 12 per cent reduction in the number of people suffering an acute respiratory tract infection.
Meanwhile, for people with the lowest levels of the vitamin, supplements cut their risk by 50 per cent.
Professor Adrian Martineau, who led the study at Queen Mary University of London, said: This major collaborative research effort has yielded the first definitive evidence that vitamin D really does protect against respiratory infections.”
Vitamin D is thought to protect against respiratory infections by boosting levels of antimicrobial peptides - natural antibiotic-like substances - in the lungs.
For many years, scientists have been trying to establish a link between respiratory infections and vitamin D, prompted by observations that these illnesses are most common in winter, when levels of the vitamin are lowest due to poor sunlight.
The data from previous studies yielded contradictory results, however, but it is now clear that this was because many of the participants were being given their supplements in big monthly doses, a practice now understood to be ineffective.
Supplements are effective when given daily or weekly, rather than in more widely spaced doses, the BMJ study concluded.
While certain foods such as oily fish contain vitamin D, most of it is obtained through sunlight on the skin, and Government advice currently states that everyone should “consider” taking supplements during the autumn and winter months to protect musculoskeletal health.
“By demonstrating this new benefit of vitamin D, our study strengthens the case for introducing food fortification to improve vitamin D levels in countries such as the UK where profound vitamin D deficiency is common,” said Professor Martineau.
Unlike countries such as Finland, the UK does not currently fortify food with Vitamin D as a matter of course, although Professor Martineau said that to do so would only cost a few pence per adult per year.
However, he added that the same preventative benefits could be derived from daily or weekly supplements.
A linked editorial in the BMJ claimed the new data only amounts to a “hypothesis...requiring confirmation”.
But Dr Benjamin Jacobs, a consultant paediatrician at the Royal National Orthopaedic Hospital, said: “The case for universal vitamin D supplements, or food fortification, is now undeniable.
"Governments and health professionals need to take Martineau’s study into account when setting Vitamin D policy now.”