A lack of sunshine in winter months could be contributing to Scotland's high rate of heart disease, researchers have said.
Researchers say dark winters can take their toll
A Dundee University team found giving people extra vitamin D over the winter was good for their blood vessels.
Scotland's record for coronary heart disease has been a cause for concern, with about 10,000 deaths every year.
The research suggests the problem may be partly caused by long, dark winters with too little sunshine.
Vitamin D is naturally produced by the skin in response to sunlight.
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.
Prof Struthers said: "Some of the things we already know about heart disease are that it is more common in northern latitudes and that deaths from heart disease are more prevalent in winter than summer.
"There may be lots of reasons for this, but one thing which our research suggests could be important is that vitamin D deficiency is very common over the winter season in Scotland."
The Diabetes UK-funded study took place over the winter of 2005-06 on people with type 2 diabetes.
Half of 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.
Prof Struthers said a wider study was now needed and warned that people should not over-expose themselves to the sun as this carried its own health risks, including skin cancer.
He said: "The safer solution in this case may be a vitamin D replacement tablet rather than overdosing on sunlight, which we would not recommend," he said.