People who suffer with persistent insomnia may have an increased risk of death, a new study has found.

Insomnia is a sleep disorder which results in people constantly having difficulties falling asleep or staying asleep. This can lead to a number of problems such as daytime fatigue, irritability, depression, poor concentration and poor coordination.

While around one in five people are thought to suffer with insomnia at any one time, around half of these suffer with chronic or persistent insomnia. US researchers decided to assess any links between the persistent type and mortality.

"We hypothesised that insomnia that was persistent over eight years, rather than intermittent insomnia, was associated with death independent of the effects of sedatives, opportunity for sleep (to distinguish it from sleep deprivation), and other confounding factors in a representative sample of the general adult community," the researcher explained.

They looked at the progress of over 1,400 adults who had taken part in a long-term study, from 1972 until 2011. They found that after taking other risk factors into account, such as age, smoking and physical activity, people who suffered with persistent insomnia were 58% more likely to die than those without insomnia.

These deaths tended to be heart-related, not cancer-related, the study noted.

It also noted that while those with intermittent insomnia also appeared to have a higher risk of death, when the other risk factors were taken into account, this increased risk was eliminated. In other words, persistent insomnia, not intermittent, increased the risk of death.

"An enhanced understanding of the association between persistence of insomnia and death would inform treatment of this ‘at-risk' population," the researchers from Arizona said.

Details of these findings are published in The American Journal of Medicine.