The lowest amounts of self-reported sleep, as measured by observed change points of sleep duration, were seen among men and women in their early 30s and early 50s, found a study published in Nature Communications.
These observed changes were found in Western, Educated, Industrialized, Rich, and Democratic (WEIRD) countries among individuals aged 33 to 53 years and in non-WEIRD countries for those aged 31 to 52 years, indicating that sleep duration is a strong function of age.
Cultural norms and latitude of self-reported sleep across countries appeared to be indirectly connected to average country-level sleep duration. In addition, a limited connection between self-reported sleep duration and performance in the first 2 phases of life was found, with a clear link only seen in the last phase, where 7 reported sleep hours corresponded to ideal memory performance.
Self-reported sleep duration looks to be linked with memory performance commencing with late midlife, with people 54 years and older sleeping more than in any other phase of life and having enhanced cognitive performance at the 7-hour sleep mark.
This study from University College London was conducted because a limited number of epidemiological studies on sleep in the general population across nations exist and have usually excluded low-income countries, which make up 84% of the global population. Researchers aimed to understand sleep duration across a much larger sample size and more expansive geographic locations.
Reported sleep durations of 730,187 participants across 63 countries were collected through the Sea Hero Quest project, “a mobile video game designed to assess navigation ability in the global population,” according to the study authors. Participants from countries with under 500 players were excluded to guarantee strong results, and the final study population was defined by 3 phases of adult life: early adulthood (19-33 years), mid-adulthood (34-53 years), and late adulthood (54 years and older).
Of the included participants, 381,153 identified as men and 349,034 as women, with a mean (SD) age of 38.71 (14.53) years.
Participants older than 70 years and those who slept less than 5 hours or more than 10 hours were excluded from the study due to a previously shown strong selection bias and the low number of representation and erroneous demographic data entry, respectively. Questions were asked about average nightly sleep, among other questions; reported sleep duration was calculated using a linear-mixed model that included factors like age, gender, education, home environment, and more.
The globally declared average of sleep duration was 7.01 hours, with women sleeping 7.5 minutes more, on average, than men (Hedge’s G = 0.12). A decrease was seen from early adulthood to age 35 years, with a plateau at age 50 years before increasing again at 70 years, where the same value is reached for 30-year-old men and 25-year-old women, indicating change points of 33 and 53 years.
These findings can help researchers understand more about self-reported sleep duration globally and the factors that influence it, and improve understanding on how sleep duration might affect health outcomes worldwide, possibly indicating areas that need to be addressed.
Due to this study being the single largest study on sleep duration across the life course, modulated by gender, geographic location, and economy, it adds a great amount of data on these influences on sleep duration worldwide that has not been known before, especially since sleep duration as a function of age looks to be strong across numerous populations, the study investigators noted.
Some limitations include the exclusion of variables like ethnicity, socioeconomic status, day of the week, levels of light, and various other factors were not measured, and the researchers recommend they would be essential to include in future studies, as well as an assessment of sleep quality confounded with sleep duration.
“Previous studies have found associations between age and sleep duration, but ours is the first large study to identify these 3 distinct phases across the life course. We found that across the globe, people sleep less during mid-adulthood, but average sleep duration varies between regions and between countries.” Said Professor Hugo Spiers, leader of the study.
Coutrot A, Lazar AS, Richards M, et al. Reported sleep duration reveals segmentation of the adult life-course into three phases. Nat Commun. 2022;13(1):1-9. doi:10.1038/s41467-022-34624-8