“Men who find themselves unable to sleep during the small hours of the night may end up dying younger,” reported the_ Daily Mail._
This study looked at people’s insomnia and their risk of dying over a 14-year period. At the start of the study, people filled out a questionnaire on their history of insomnia and were observed for one night in a sleep laboratory. Men who reported a history of insomnia and slept for less than six hours in the lab were four times more likely to die in the follow-up period than those without insomnia who slept for six hours or more in the lab.
These findings require careful interpretation and do not prove that insomnia increases the risk of early death. Sleep duration was only objectively measured once, so it may not represent a typical sleep pattern or confirm that a person had insomnia. In addition, the study’s middle-aged participants were originally enrolled to investigate sleep disordered breathing, so they were not randomly selected and are unlikely to represent the general population.
In short, this research does not provide strong evidence that insomnia is linked to an early death, and it sheds no light on possible reasons behind a link. Further research is needed.
The study was carried out by researchers from Pennsylvania State University College of Medicine in the US, and was funded by the National Institutes of Health. It was published in the peer-reviewed scientific journal Sleep.
The study was widely reported in the media. Few reports looked at the study’s limitations.
This prospective cohort study examined whether insomnia and getting less than six hours a night affected the risk of death from any cause. The participants reported their insomnia themselves, and sleep duration was measured in a single night’s observation in a sleep laboratory.
This type of study, in which large groups of people are followed over time, are useful in assessing whether conditions or circumstances (in this case, insomnia and objectively measured sleep duration) are associated with later events (here, mortality). However, this cohort is limited in that it is a secondary analysis of a group of participants who were originally enrolled to investigate the age distribution of people with sleep disordered breathing.
The researchers point out that insomnia has never been linked to any serious medical disorders, such as cardiovascular problems. However, recent research has associated it as a risk factor for high blood pressure and diabetes. They speculate that severe insomnia is likely to be associated with higher mortality, saying this theory is supported by studies showing that insomniacs suffer from increased heart and metabolic rates and impaired heart rate variability.
The researchers say that previous findings relating to insomnia and mortality have been inconsistent. They point out that these studies relied only on self-reported sleep disturbance, did not measure sleep duration objectively, and did not always control for confounders. Here, they aimed to examine the association between insomnia and mortality while taking these factors into account.
The research was the secondary analysis of a larger study on sleep-disordered breathing. That larger study interviewed 16,583 people by telephone, asking them questions about their sleep habits. From this cohort, 741 men of average age 50, and 1,000 women of average age 47, agreed to take part in the sleep analysis study (representing 67.8% of men and 65.8% of women who had been asked to take part).. This selection was not random, and the researchers say that they had chosen a larger-than-usual proportion of people with a high BMI and who were at greater risk of sleep-disordered breathing.
All participants completed a comprehensive sleep history questionnaire and physical examination. Their sleep was evaluated for one night in the sleep laboratory, using polysomnography, a comprehensive recording of all biophysical changes that occur during sleep. They were then divided into two categories according to how long they had slept. Those who slept six hours or more were put in the normal sleep duration group, while those who slept less than six hours were in the short duration group.
On the same evening as the laboratory visit, the group also filled in a standardised questionnaire covering demographics, sleep-related questions (including questions on sleep disorders) and general health questions. The presence of insomnia was defined as insomnia that had lasted for at least one year.
The men in the study were followed up for 14 years, and the women for 10 years. People who died were identified using social security numbers matched to federal and state death record services. The possible association between insomnia, objectively measured sleep duration and the risk of mortality was assessed using standard statistical methods. The findings were adjusted to take account of possible confounders, such as age, race, education, body mass index, smoking, alcohol, depression and sleep-disordered breathing. The participants were also asked if they were being treated for diabetes or high blood pressure.
Overall, during the study period, 21% of men and 5% of women died. The main findings are as follows:
Men with chronic insomnia and objectively measured short sleep duration had a higher risk of dying early, say the researchers, independent of other factors associated with mortality. People who had diabetes or high blood pressure showed a far stronger association between insomnia and short sleep duration. They say that the diagnosis and treatment of insomnia should be targeted by public health policy.
This study has found that in middle-aged men, self-reported insomnia and objectively measured short sleep duration was associated with a greater risk of death during the 14-year follow-up period, compared with men who did not have insomnia or short sleep duration. However, these findings require careful interpretation and do not prove that insomnia increases the risk of early death:
To sum up, this research is not strong evidence that insomnia is linked to an early death, and it sheds no light on possible reasons behind a link. Further research is needed.