You can read how researchers from the Pennsylvania State University College of Medicine, in Hershey, Pennsylvania, came to these findings in a paper they wrote that was published on 1 September in the journal SLEEP.
The study is thought to be the first to show that chronic insomnia, coupled with short sleep as measured objectively in a lab (as opposed to self-reported in questionnaires), is linked to higher mortality in men.
Previous studies using objective measures of sleep duration have shown a link between this particular subset of insomnia and poorer health, but have not investigated association with mortality, said the authors in their background information.
First author and pricipal investigator Dr Alexandros N Vgontzas, who is professor of psychiatry in the Department of Psychiatry at Penn State College of Medicine and Hershey Medical Center, told the media that:
"The primary finding of our study is that insomnia, the most common sleep disorder, is associated with significant mortality in men."
"Our different results are based on our novel approach to define insomnia both on a subjective complaint and the objective physiological marker of short sleep duration measured in the sleep lab," he added.
Insomnia is where a person finds it difficult to get to sleep, and then once they are asleep, they experience periods of wakefulness where they find it hard to get back to sleep again. The quality of sleep is so poor that it also affects their performance during the day.
The researchers defined chronic insomnia as having insomnia for at least one year.
For the study, 1,000 women of average age 47 and 741 men of average age 50 years, provided a comprehensive sleep history, underwent a physical exam and slept one night in a laboratory so their sleep duration could be measured objectively with a polysomnograph.
When they analysed the results for links between insomnia sleep duration and mortality, the researchers adjusted for potential confounders, including age, race, education, body mass index, smoking status, alcohol consumption, depression, and sleep disordered breathing. They also adjusted for disease factors such as diabetes and hypertension.
The results showed that:
- The group was followed for about 10 years in the case of the women and 14 years in the case of the men.
- During the follow up, a total of 248 (14 per cent) participants died: 145 (21 per cent) of the men and 103 (5 per cent) of the women.
- 8 per cent of the women and 4 per cent of the men had chronic insomnia with a sleep duration of less than six hours.
- The 14-year adjusted mortality rate for men was 9.1 per cent for those without chronic insomnia who slept for at least 6 hours, and 51.1 per cent for those with chronic insomnia who slept less than 6 hours.
- There was no such link between mortality and insomnia with short sleep duration among the women.
- There was a slightly higher risk of death among participants with chronic insomnia and short sleep who also had diabetes or hypertension.
"Insomnia with objective short sleep duration in men is associated with increased mortality, a risk that has been underestimated."
Other researchers have done studies using data from this same group of participants and found that chronic insomnia with short sleep duration are linked to higher risk of type 2 diabetes and hypertension, plus neurocognitive deficits.
Vgontzas said he hoped that this latest study, along with the previous ones, will increase awareness among health professionals so that insomnia is diagnosed early and treated appropriately.
The researchers pointed out that their use of the 6-hour threshold should not be interpreted as an ideal length of a good night's sleep, it was merely a useful cut-off point for the study.
The American Academy of Sleep Medicine says most adults need seven to eight hours of sleep to feel alert and well rested during the day.
Speculating on why the findings only seem to apply to men, the researchers suggested one possibility was the difference in amount of data between the men and the women: the women were followed for less time and fewer of them died compared to the men: leaving open the possibility that, had they been followed for the same length of time, the outcomes could have been more similar.
"Insomnia with Short Sleep Duration and Mortality: The Penn State Cohort."
Vgontzas AN; Liao D; Pejovic S; Calhoun S; Karataraki M; Basta M; Fernández-Mendoza J; Bixler EO.
SLEEP, Volume 33, Issue 09, pp 1159-1164, published 01 September 2010.
Source: American Academy of Sleep Medicine.