British people - and others living in the Northern Hemisphere - need five to 30 minutes of sunlight on bare skin a few times a week to generate enough Vitamin D to prevent against diseases like cancer.
Those who had chronically-low levels of the vitamin have 30 per cent more mortality rates and are also 40 per cent more likely to get tumorous growths, a research of 96,000 people shows.
The study - which followed Danish people for 40 years to take blood samples and track their lifestyle and diet - shows that, in a country where the sun sets as early as 3.30pm in December, most people get one fifth of their Vitamin D from food and four fifths from direct sunlight. Decreased levels of Vitamin D can also contribute to risks of heart disease, diabetes, depression and bone pain, the National Health Service says.
As the sun is not at its peak during the winter, those low in the vitamin are advised to eat Vitamin D-packed foods such as omega-3 rich fish, milk and eggs and potentially take supplements that are available from chemists or with a doctor's prescription for higher doses.
Researchers at Copenhagen University Hospital said, although additional Vitamin D is proven to be beneficial from cold months October to March, it is not yet known which way is best to produce or administer it.