Scotland's gloomy winters could be one of the causes of the country's high rate of heart disease, according to scientists.

A team from Dundee University gave a group of volunteers a dose of vitamin D, the sunshine vitamin, over the winter and found it improved their blood-vessel function.

They believe this could be the key to cutting some of the 10,000 deaths a year from heart attacks in Scotland.

Vitamin D is naturally produced by the skin in response to sunlight but in countries like Scotland a lack of sun in winter means the skin produces virtually none.

The researchers, led by Professor Allan Struthers of the university's medical school, presented their findings at the British Cardiovascular Society's annual conference in Glasgow yesterday.

Professor Struthers said: "Heart disease is more common in northern latitudes and deaths from heart disease are more prevalent in winter than summer. There may be lots of reasons for this but one thing our research suggests could be important is that vitamin D deficiency is very common over winter in Scotland."

The Diabetes UK-funded study took place over the winter of 2005-06 on people with type 2 diabetes. Half the patients taking part in the trial were given a single high dose of vitamin D.

Months later, they were found to have improved vascular function, with no adverse effects. In patients who were given a placebo, blood vessel function remained fairly stable. Mr Struthers said a wider study was now needed.

"Of the routine diabetic patients we surveyed in Tayside, 50% were vitamin D-deficient in winter," he said.

Sunshine vitamin' key to cutting deaths

"That figure rises to 70% to 80% in patients with heart failure or strokes and we now need to see if vitamin D benefits those patients also.

"The study suggests, really for the first time, that vitamin D has a beneficial effect on the blood vessel. That's what's excitingly new.

"It was a small group but the findings fit very nicely with what we already know - that heart disease is more common in northern latitudes, deaths from heart disease are more prevalent in winter than summer, and in Scotland we don't make any vitamin D in the winter time."

Mr Struthers hopes one day a single autumn dose of the vitamin could be given to protect groups at risk of not only heart attack but also stroke right through the winter.

He said: "One of the good things about vitamin D is that it is a fairly non-toxic substance and giving one pill every two or three months would be much easier for people than having to take a pill every day."

He said they were neither recommending the population in general took vitamin D tablets or tried to expose themselves to more sunshine.

He said those patients who had been given vitamin D in the trial had been vitamin D deficient, something people would not be aware of without testing.

However, he said it was entirely possible, at some stage in the future, people's vitamin D might be measured, particularly in winter, as part of health screening in the same way as cholesterol and blood pressure are at the moment.

"We are not advocating sunlight because it might increase the risk of skin cancer," he said.

However, he did advocate eating oily fish, which had other health properties, as a dietary step to obtain a very small amount of vitamin D.