Acute insomnia can be due to anxiety about an important event.
While previous studies have already shown links between insomnia and increased risk of premature death, they have not clarified whether the risk differs between persistent and intermittent insomnia.
Intermittent or acute insomnia is of short duration and often linked to specific events - for instance, not being able to fall asleep the night before an exam or an important job interview.
Persistent or chronic insomnia is a long-term pattern of disrupted sleep on several nights a week that lasts for months and years and can be due to a number of causes, including shift working, poor sleep habits and medication use.
In the US, around 20% of adults are affected by insomnia, half of whom suffer from persistent insomnia.
For their study, researchers from the University of Arizona in Tucson sought to clarify if the link between insomnia and raised risk of premature death depended on the type of insomnia. They also looked at whether there was a difference in inflammation.
Knowing how persistence of insomnia affects risk of death might affect treatment decisions
The researchers had a hunch that the inability to get a good night's sleep that goes on for years has a direct effect on the risk of death, regardless of the underlying reasons for it.
Lead investigator Sairam Parthasarathy, associate professor of medicine at the University of Arizona College of Medicine, explains:
"We hypothesized that insomnia that was persistent over 8 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.
An enhanced understanding of the association between persistence of insomnia and death would inform treatment of the 'at-risk' population."
For their study, Prof. Parthasarathy - who is also director of the Center for Sleep Disorders at the University of Arizona Medical Center - and colleagues examined data from 1,409 adults who took part in the Tucson Epidemiological Study of Airway Obstructive Disease (TESAOD).
Participants were enrolled in 1972 and surveyed and examined until 1996. After that, deaths in the group continued to be monitored until 2011, making a total study period of 38 years.
Persistent insomnia linked to 58% higher risk of death
The researchers were able to test cryopreserved blood samples that were collected at the start and at intervals over the study period. The participants completed questionnaires about their sleep habits twice - once between 1984 and 1985 and again between 1990 and 1992.
The team put the participants into one of three categories:
- Persistent insomnia - insomnia was present in both questionnaires completed in 1984-1985 and 1990 -1992
- Intermittent insomnia - insomnia was present in either but not both questionnaires
- Never insomnia - insomnia was not present in either questionnaire.
When they analyzed the results, the researchers adjusted for factors that might influence any links between insomnia and risk of death, such as age, sex, weight, smoking status, use of sleep medication and exercise.
After taking the potential confounders into account, they found that participants with persistent insomnia had a 58% higher chance of dying during the study than participants in the never insomnia group.
The results also indicated that the excess deaths in the persistent insomnia group were due to cardiopulmonary factors rather than cancer.
Inflammation levels also higher in persistent insomnia group
While members of the intermittent insomnia group appeared to have a higher risk of dying in the study period than those of the never insomnia group, the researchers found this risk went away when they adjusted for factors such as weight, smoking status and exercise.
From the blood sample analysis, the team also found that levels of C-reactive protein (CRP) - a measure of inflammation that is also an independent risk factor for mortality - were higher in the persistent insomnia group.
And when they adjusted the link between persistent insomnia and raised risk of death to take into account CRP levels, the researchers found there was still a raised risk of death of 36% for participants with persistent insomnia.
Meanwhile, as this study uncovers the risks associated with lack of sleep, Medical News Today recently learned how too much sleep could increase the risk of stroke. In the journal Neurology, researchers at the University of Cambridge in the UK describe how they analyzed the sleeping habits and health of 9,000 people and concluded that sleeping more than 8 hours a night was tied to a 46% increased risk of stroke.