Jennifer Lovejoy, Arivale Chief Science Officer, PhD
[Arivale Hot Topics address health stories currently in the news. The Arivale Clinical Team’s commentary on these news articles is not a review of the scientific evidence, nor an endorsement of a specific study, and is not meant as official medical opinion.]
Sleep can be a tricky thing. Too little has been associated with multiple health issues – heart problems, a growing waistline, and anxiety and depression, for example – but so has too much sleep. Many studies demonstrate that both “short” and “long” sleep are associated with higher mortality – or the risk of dying.
Still, published results are not consistent. Most studies don’t distinguish between amount of sleep on weekdays versus weekends, which may differ dramatically due to work and school schedules.
There’s a lack of research on whether weekend sleep duration or different patterns of weekday and weekend sleep duration are associated with mortality. For example, is it possible that sleeping longer on the weekends can compensate – in terms of mortality – for shorter weekday sleep?
At the beginning of the study, nearly 44,000 adult participants from the Swedish National March Cohort were asked two sleep duration questions: “How many hours, approximately, do you usually sleep during a workday/weekday night?” and “How many hours, approximately, do you usually sleep per night on days off?” Participants were followed for 13 years, and deaths and causes of death were recorded.
The researchers accounted for factors that may be associated with mortality as well as with sleep, such as education, body mass index, disease status, and lifestyle factors.
Over the 13 years, the main causes of death were cancer and cardiovascular disease. The research confirmed previous studies showing that consistently short sleep – five hours or less per night – as well as consistently long sleep – nine or more hours per night – were associated with higher mortality risk.
Most interestingly, long weekend sleep after short weekday sleep – in other words, sleeping in on the weekends – wasn’t associated with increased mortality. Researchers also found that long weekend sleep wasn’t associated with an increased mortality risk – but short weekend sleep was.
No significant associations between sleep duration and death were observed in participants over the age of 65. This could be an effect of biological aging or of reduced demands in life (work, family, etc.). However, the issue needs further research.
Based on these results, researchers hypothesize that in those under 65, it’s possible long weekend sleep may compensate for short weekday sleep in terms of overall mortality risk. However, as the researchers themselves mention, this interpretation of weekend sleep being compensatory sleep is just speculative. To confirm this, it needs studies that link mortality to changes in sleep duration between weekend and weekday over time.
There are some important limitations of this study – only the last of which was addressed in CNN’s coverage of it.
Researchers only measured sleep duration once (at the beginning of the study). After enrollment into the study, changes in sleep duration over time might occur due to health, work, or life changes; and one could speculate that these changes in sleep duration would be associated with mortality. Ideally, repeated measurements of sleep duration using follow-up questionnaires would have helped keep track of changes in sleep habits.
The study also only looked at one outcome – overall mortality. While this is obviously important, it’s well known that lack of sleep contributes to many other important outcomes that relate to both physical health and quality of life. It’s not known at this time whether compensatory weekend sleep would have benefits on these other outcomes.
Lastly, sleep duration was measured via a questionnaire, which is subject to some recall and interpretation error, rather than by objective means such as an activity or sleep monitor.
It’s too early to tell if getting extra shut eye on the weekend will make up for lack of sleep on weekdays. However, research does show that getting adequate sleep – seven to nine hours for adults under the age of 65 – consistently – meaning both weekdays and weekends – is best for health.