We spend a third of our lives sleeping and the importance of sleep for our health is no longer in question. It regulates several functions including mood, cognition, metabolism and immunity. Moreover, several scientific studies have observed an association between the duration of sleep, whether short or long, and the development of a chronic disease (such as cancer or cardiovascular disease).
As populations age, their sleep patterns change. More than half of adults over the age of 65 are known to have two or more chronic diseases. While current recommendations [1] call for 7-8 hours of sleep per night, whether or not sleep duration in mid- to late-life increases the risk of multimorbidity has not been studied.
Scientists from Inserm and Université Paris Cité have examined how sleep duration is associated with the evolution of chronic diseases during aging. They used data from 7,000 British people collected as part of the Whitehall II study [2] at University College London.
Participants completed a self-assessment of their sleep duration on several occasions between 1985 and 2019 which allowed the extraction of data on sleep duration at age 50, 60, and 70 for each participant. One group of participants (4,000 people) also wore a connected (or accelerometer) watch for a week, which provided an accurate measure of sleep duration and verified the accuracy of the estimates. These data were cross-referenced with information on participants’ health status obtained during follow-up [3] through March 2019.
The researchers were thus able to examine the relationship between sleep duration at different ages, its evolution between 50 and 70 years of age, and the risk of occurrence of multimorbidity. They also specifically studied the role of sleep duration at age 50 in the risk of transition from a healthy state to a first chronic disease, to multimorbidity and to mortality.
The results obtained first suggest that there is a robust association between short sleep duration (less than or equal to 5 hours) at the ages of 50, 60, and 70 years and a higher risk of multimorbidity of the order of 30 to 40% depending on age.
The authors also observed that short sleep duration at age 50 was associated with a 20% increased risk of developing a first chronic disease, and a similar increased risk of multimorbidity among those who had already developed a first chronic disease.
These results could explain the 25% increased risk of death observed in people aged 50 years with a sleep duration of less than or equal to five hours per night. Indeed, short nights of sleep increase the risk of developing one or more chronic diseases, and the latter are associated with a shorter life expectancy.
Finally, the scientists did not find a robust association between having a longer sleep duration (greater than or equal to 9 hours) at age 50 years and the risk of developing multimorbidity in aging. In contrast, a night’s sleep of 9 hours or more among those who developed a first chronic disease during follow-up (at a mean age of 66 years) was associated with an increased risk of developing multimorbidity. This result suggests that a long night’s sleep may be the consequence of a chronic disease rather than its cause. Future studies on the subject are needed to confirm this hypothesis.
"All of these results support the importance of promoting good sleep hygiene in populations. To do this, it is necessary to target lifestyle habits and environmental conditions that affect the duration and quality of sleep," explains Séverine Sabia, Inserm researcher and first author of the study.
[1] Hirshkowitz M, Whiton K, Albert SM, Alessi C, Bruni O, DonCarlos L, et al. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health. 2015.
[2] As part of the follow-up of the British Whitehall II cohort, scientists are examining the impact of social, economic, biological and lifestyle factors on long-term health.
[3] Health information is obtained through questionnaires and clinical examinations carried out every 5 years as part of the cohort follow-up (blood tests and electrocardiograms). It is completed by electronic health data (access to the hospitalization register, for example).
Press release - Inserm Press Room Link: https: //presse.inserm.fr/de-courtes-nuits-de-sommeil-des-50-ans-augmenteraient-le-risque-de-developper-plusieurs-maladies-chroniques/45917/
