Vitamin D supplements could prevent over three million people across the UK developing colds or the flu each year, according to researchers.
The vitamin is vital for bone and muscle health but a new study claims it also protects against acute respiratory infections.
The findings published in the British medical Journal say taking supplements of the vitamin can help prevent against colds and flu.
Results of the study fit with the observation that colds and flu are most common during winter and spring, when levels of vitamin D are at their lowest.
Vitamin D supplements has been a hot topic in medical circles in recent years with some experts arguing that their usefulness remains uncertain.
The new research, led by academics from Queen Mary University of London (QMUL), analysed data from almost 11,000 people aged up to 95 who took part in 25 clinical trials conducted in 14 countries, including the UK.
Lead researcher Professor 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."
Experts said that the study had implications for public health policy, including the possibility of fortification of foods with vitamin D to tackle high levels of deficiency in the UK.
Vitamin D is created in the skin while out in the sun so therefore during winter months people generally have low levels in countries like the UK.
Last year, Public Health England said that people were generally not getting the recommended 10 micrograms of vitamin D a day from sunlight in winter.
The research showed that the protective effects of vitamin D supplements are strongest in those who have lower levels and also those who take the pills daily or weekly.
Professor Martineau added: "Vitamin D fortification of foods provides a steady, low-level intake of vitamin D that has virtually eliminated profound vitamin D deficiency in several countries.
Researchers say the new benefit found in the study strengthens the case for introducing food fortification to improve vitamin D levels in countries such as the UK where vitamin D deficiency is common.
However other experts suggest that the evidence in the study does not support the use of vitamin D supplementation to prevent colds or flu.
The head of nutrition science at Public Health England, Professor Louis Levy said: "The evidence on vitamin D and infection is inconsistent and this study does not provide sufficient evidence to support recommending vitamin D for reducing the risk of respiratory tract infections."