Heart failure may be linked to a lack of vitamin D, researchers have found.
Vitamin D is synthesised by exposure to sunlight
German scientists have found that levels of the vitamin are considerably lower in the blood of patients with chronic heart failure.
The potentially fatal condition results from the failure of the heart to pump blood around the body in sufficient quantity, depriving the organs of a proper supply of nutrients and oxygen.
Patients become tired after the slightest exertion, their pulse rate soars and their kidneys cease to function properly.
Researchers from University of Bonn, in co-operation with the Bad Oeynhausen Heart Centre focused on vitamin D as there was previous animal research suggesting a possible link to heart failure.
For instance, chicks with vitamin D deficiency had been shown to develop heart failure, which disappeared as soon as the vitamin was added to their feed.
They compared 54 patients with chronic heart failure with 34 healthy people, and found that vitamin D levels were up to 50% lower in the blood of CHF patients.
And the more severe the vitamin D deficiency, the worse the symptoms of heart failure appeared to be.
The researchers now plan to check whether giving CHF patients vitamin D can help to improve their condition.
The researchers believe vitamin D plays a central role in regulating calcium concentration in cells of the heart muscle.
The heart has its own blood supply
If calcium levels are not precisely controlled, the muscle cells are unable to expand and contract properly, and thus blood cannot be pumped effectively around the body.
Human beings make vitamin D themselves. The great majority is synthesised from ultraviolet radiation from the sun.
However, lack of exposure to the sun's rays - and consequently vitamin D deficiency - is becoming an increasing problem in societies where many people work in offices and go home to sit in front of a TV or PC all evening.
Researcher Dr Armin Zittermann said it was possible that people with CHF were trapped in a vicious circle - lack of vitamin D contributed to their medical condition, which in turn prevented them from going outside to synthesise new supplies.
However, he said diet, rather than sunbathing was the best way to top up vitamin D levels as ultraviolet radiation could cause skin cancer.
Professor Henry Dargie, an expert in cardiology at the University of Glasgow, told BBC News Online the link between vitamin D and heart failure sounded plausible.
However, he said: "I am not aware that the epidemiology of heart failure varies with the amount of sunlight - ie you would expect much higher levels in Nordic countries as compared with southern Europe."
Belinda Linden, of the British Heart Foundation, said: "Vitamin D deficiency can lead to low levels of calcium and to rickets, osteomalacia and a high risk of bone fractures.
"Severe deficiency of calcium can also affect the electrical activity of the heart.
"This small study is the first to explore this area in more depth - and the authors are keen to suggest that this is not conclusive."
The research is published in the Journal of the American College of Cardiology.