People who have trouble drifting off to sleep may be at increased risk of heart failure, researchers say. The study, published in the European Heart Journal, followed more than 50,000 people for 11 years. Scientists found those who suffered several nights of poor sleep were more likely to develop the condition, in which the heart fails to pump properly. Experts say further research is needed to see if a lack of sleep causes heart failure or the link is more complex. Scientists at the Norwegian University of Science and Technology looked at more than 50,000 people aged between 20 and 89. At the beginning of the study, none of them were known to have heart failure. In this condition the muscles of the heart are often too out of shape to do their job properly - they may be too weak or too stiff to pump blood around the body at the right pressure. More than 750,000 people in the UK have heart failure and for the majority there is no cure. People with the disorder may feel increasingly breathless and exhausted. And as heart failure worsens, it can be difficult to get a full night's rest - but the Norwegian study is one of few to investigate whether poor sleepers without the condition are at risk of getting it in later life. 'Stress hormones' During the research, the participants were asked whether they had any difficulties getting to sleep or staying asleep and whether they felt fully restored after a night's slumber. People who had trouble falling asleep and remaining asleep each night were three times more likely to develop heart failure than those who reported no trouble sleeping. Those who experienced substandard sleep that failed to leave them fully refreshed were also at risk. And this link between a bad night's sleep and heart failure remained true despite researchers taking smoking, obesity and other well known triggers of insomnia and heart problems into account. The researchers say it is unclear exactly why poor sleep and heart failure are associated in this way. Dr Laugsand, lead author of the study, said: "We don't know whether insomnia truly causes heart failure. But if it does, the good thing is it is a potentially treatable condition. "So evaluating sleep problems might provide additional information in the prevention of heart failure." He suggests the lack of sleep may provoke harmful responses in the body. "When you have insomnia your body releases stress hormones which in turn may effect the heart in a negative way," he said.. The same team of researchers have previously reported a link between people prone toinsomnia and heart attacks. 'Unpleasant condition' And diabetes, depression and poor brain function have all been linked to missing restful hours in bed. Dr Tim Chico, senior clinical lecturer at the University of Sheffield said: "This is an association study - it links insomnia to heart failure, but does not prove that insomnia causes heart failure or vice versa. Studies like this raise interesting suggestions that need further work to examine. "Insomnia is a very unpleasant condition, but there are effective lifestyle changes that can reduce it, such as weight loss and exercise. "Luckily many of the things that reduce the chance of heart failure also reduce insomnia - good diet, exercise, weight loss and not smoking." June Davison, senior cardiac nurse at the British Heart Foundation, said: "This research shows a link between insomnia and your heart, but this doesn't mean sleepless nights cause heart failure. "It's well known that getting enough sleep is vital for your mental, physical and emotional wellbeing. "Trouble drifting off can be helped by taking a warm bath to relax, or avoiding caffeine and heavy meals too close to the end of the day. "If lack of sleep is becoming a problem and affecting your daily life, have a chat with your GP."