[I could only dream of six or seven hours' shut-eye. Fortunately I'm over 65.]
Many people complain they do not get enough sleep, and it seems they are right to be concerned. Researchers have found that adults under the age of 65 who get five or fewer hours of sleep for seven days a week have a higher risk of death than those who consistently get six or seven hours’ shut-eye.
However the effect of short sleeps over a few days may be countered by a later lie-in. The research found that individuals who managed just a few hours’ sleep each day during the week but then had a long snooze at weekends had no raised mortality risk, compared with those who consistently stuck to six or seven hours a night.
“Sleep duration is important for longevity,” said Torbjörn Åkerstedt, first author of the study, at the Stress Research Institute, Stockholm University, and Karolinska Institute, also in the Swedish capital.
The study, published in the Journal of Sleep Research, is based on data from more than 38,000 adults, collected during a lifestyle and medical survey conducted throughout Sweden in 1997. The fate of participants was followed for up to 13 years, using a national death register.
Åkerstedt said researchers had previously looked at links between sleep duration and mortality but had focused on sleep during the working week. “I suspected there might be some modification if you included also weekend sleep, or day-off sleep.”
Once factors such as gender, body mass index, smoking, physical activity and shift work, were taken into account, the results revealed that those under the age of 65 who got five hours of sleep or under that amount seven days a week had a 65% higher mortality rate than those getting six or seven hours’ sleep every day. But there was no increased risk of death for those who slept five or fewer hours during the week but then managed eight or more hours’ sleep on weekend days.
“The assumption in this is that weekend sleep is a catch-up sleep,” said Åkerstedt, though he noted the study did not prove that to be the case.
However, people who slept for eight or more hours, seven days a week, were found to have a 25% higher mortality rate compared with those who kept to six or seven hours a day.
The study also found that the link between sleep patterns and mortality disappeared for those aged 65 or older. That, Åkerstedt said, was perhaps because older individuals got the sleep they needed.
Average sleep duration at weekends and the percentage of those saying they did not feel rested at waking, did fall with age. Across the week, older people had more consistent and more often sleep over a shorter time span.
While the study did not investigate the link between sleep patterns and mortality rates, Åkerstedt said it was possible little sleep had a negative effect on the body, while consistently lengthy sleep could be a sign of underlying health problems.
The study had limitations; participants were only asked about their sleep patterns at one point in time. But Stuart Peirson, an expert on the human “body clock” but who was not involved in the research, said the study offered a more nuanced view than previous research, which had suggested that both very little or a lot of sleep was bad for health and longevity.
“It fits with what we do know about sleep – that sleep is regulated by the body clock but also regulated by what is called a homeostatic process, which means the longer you are awake the more you need to sleep.”
Peirson, based at the University of Oxford, noted that sleep requirements varied from person to person according to genetics, but he added that “sleep debt” needed to be “paid off”. He said: “You can’t keep burning the candle at both ends. Well, you can, but you won’t live as long.”
Åkerstedt T, Ghilotti F, Grotta A, Zhao H, Adami HO, Trolle-Lagerros Y, Bellocco R. Sleep duration and mortality - Does weekend sleep matter? J Sleep Res. 2018 May 22:e12712. doi: 10.1111/jsr.12712. [Epub ahead of print]
Previous studies have found a U-shaped relationship between mortality and (weekday) sleep duration. We here address the association of both weekday and weekend sleep duration with overall mortality. A cohort of 43,880 subjects was followed for 13 years through record-linkages. Cox proportional hazards regression models with attained age as time-scale were fitted to estimate multivariable-adjusted hazard ratios and 95% confidence intervals for mortality; stratified analyses on age (<65 years, ≥65 years) were conducted. Among individuals <65 years old, short sleep (≤5 hr) during weekends at baseline was associated with a 52% higher mortality rate (hazard ratios 1.52; 95% confidence intervals 1.15-2.02) compared with the reference group (7 hr), while no association was observed for long (≥9 hr) weekend sleep. When, instead, different combinations of weekday and weekend sleep durations were analysed, we observed a detrimental association with consistently sleeping ≤5 hr (hazard ratios 1.65; 95% confidence intervals 1.22-2.23) or ≥8 hr (hazard ratios 1.25; 95% confidence intervals 1.05-1.50), compared with consistently sleeping 6-7 hr per day (reference). The mortality rate among participants with short sleep during weekdays, but long sleep during weekends, did not differ from the rate of the reference group. Among individuals ≥65 years old, no association between weekend sleep or weekday/weekend sleep durations and mortality was observed. In conclusion, short, but not long, weekend sleep was associated with an increased mortality in subjects <65 years. In the same age group, short sleep (or long sleep) on both weekdays and weekend showed increased mortality. Possibly, long weekend sleep may compensate for short weekday sleep.