People naturally get less vitamin D from the sun in the winter and that may be why they are more susceptible to respiratory infections like the flu. New research from the University of Surrey in England shows that low vitamin D levels are linked to a much higher risk of hospitalization from severe respiratory infections.

Scientists found that those with what they called a severe vitamin D deficiency (below 15 nmol/L) were 33 percent more likely to be admitted to a hospital for treatment for things such as bronchitis or pneumonia than those with levels of at least 75 nmol/L. And the hospitalization rate decreased by 4 percent for every 10 nmol/L increase in vitamin D.

"Vitamin D is vital to our physical well-being," said, Abi Bournot, lead author. "Not only does it keep our bones and muscles healthy, its antibacterial and antiviral properties are also thought to help reduce the risk of respiratory tract infections that can lead to hospitalization.

"This research attaches hard data to support the theory. Despite its importance to our overall health, many people are deficient and do not meet the government's recommended intake of 10 micrograms of vitamin D per day."

Respiratory tract infections are in the top 20 leading causes of death across the globe for people between the ages of 50-74, and it's in the top 10 for those over the age of 75.

"Supplementation of the vitamin, especially in the winter months when our exposure to sunlight is limited, is an effective way of increasing vitamin D and reducing the risk of serious respiratory tract infections," Bournot said. "This is particularly important for older people who are at higher risk of death from such infections, and ethnic minority communities in the UK, who are at a higher risk of vitamin D deficiency."

"Respiratory tract infections are a major threat to public health globally," said Dr. Andrea Darling, senior author of the study. "Not only can they make an individual feel very unwell in many cases, they can also lead to hospitalization which puts strain on an already stretched health service.

"Our findings of a significant association between increased vitamin D levels in our bodies and reduced hospital admission rates warrants further study, and points to the potential for vitamin D supplementation and consumption of vitamin D fortified foods to reduce the risk of hospitalization with respiratory infections in the future, and therefore mitigate pressures on the NHS."

Click here to read more in The American Journal of Clinical Nutrition.