Children with insomnia and shorter sleep duration may have impaired modulation of heart rhythm during sleep, researchers have reported.

In a study of young children, researchers showed that insomnia symptoms were consistently associated with impaired heart variability measures. They also found a significant but less consistent pattern with shortened sleep duration and decreased heart rate variability.

Heart rate variability is the beat-to-beat variations of heart rate. In a healthy person, beat-to-beat intervals change slightly in response to automatic functions like breathing.

The study included 612 elementary school children in the first to fifth grades. All were generally in good health. Their parents completed the Pediatric Behaviour Scale, including two questions that focused on symptoms of insomnia.

Researchers examined the children overnight in a sleep laboratory with polysomnography (PSG), a standardized method for measuring sleep disorders. The researchers measured sleep duration, trouble falling asleep, the number of wake-ups and problems going back to sleep if awakened. They also measured cardiac autonomic modulation (CAM), the balance of the sympathetic and the parasympathetic control of the heart rate rhythm.

A balance is needed between the sympathetic modulation that 'excites' the heart and the parasympathetic modulation that 'calms' the heart, said Fan He, the lead-author of the study. 'The balance between the sympathetic and the parasympathetic provides a favourable profile for the heart.'

The study found that the heart rate of children who slept eight hours was two beats per minute slower than that of kids who slept only seven hours.

Parents should encourage their children to have healthy bedtime habits that encourage sleep, Duanping Liao, professor at Penn State, said. 'Watching television before going to bed and waking up to return text messages are examples of activities that could have a harmful affect on healthy sleep patterns in children.'

Liao called for further studies in children to determine the impact of sleep deprivation and stress and the possible long-term risk of cardiovascular disease and obesity. 'Previous studies have shown a strong association of heart rhythm regulation and heart risk in adults. It's quite possible that this kind of stress can have a long-term impact even at a young age.'

The findings were presented at the American Heart Association's 50th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.