Researchers at the University of Hawaii have found that a lack of vitamin D -- which is naturally produced by the skin when exposed to strong sunlight and is also found in foods including nuts and oily fish -- can raise stroke risk by more than a fifth.
Based on their 34-year-long study involving about 7,500 middle-aged and elderly people, the team discovered that the quarter of people with the lowest vitamin D levels were at a 22 per cent higher risk of having a stroke than those in the top quarter.
Low vitamin D levels increased the chance of having the more common type of stroke, known as an ischaemic stroke, where a clot becomes lodged in a brain blood vessel.
However, low levels did not affect the likelihood of the other type, called a haemorrhagic stroke, caused by a burst brain blood vessel, the researchers found.
Dr Gotaro Kojima, one of the study researchers, said getting vitamin D from food or supplements was of greater importance for older people because synthesising the vitamin from sunlight becomes more difficult with age.
"Our study confirms that eating foods rich in vitamin D might be beneficial for stroke prevention," Kojima was quoted as saying by the Sunday Telegraph.
"Based on the results of this and other epidemiological studies, higher vitamin D intake or vitamin D supplementation may be beneficial for stroke prevention," Kojima advised.
However, the researchers said large randomised controlled trials, specifically designed to test the theory, were needed.
The new findings are published in the American Heart Association journal Stroke.