Most parents think the answer to a tired child is simple: put them to bed earlier. Give them more time to sleep. But a 2024 study from Australia challenges that assumption in a way that every sleep consultant should understand.
The study, titled “Time use and dimensions of healthy sleep: A cross-sectional study of Australian children and adults,” was published in Sleep Health by Matricciani, Dumuid, Stanford, Maher, Bennett, Bobrovskaya, Murphy and Olds at the University of South Australia. The researchers examined how the full 24-hour day, not just bedtime habits, relates to different dimensions of sleep in 1168 children and 1360 adults. Their most striking finding: simply allocating more time to sleep was associated with less efficient sleep.
How the study worked
The data came from the Australian Child Health CheckPoint study, conducted between February 2015 and March 2016. It was nested within the Longitudinal Study of Australian Children.
The children had a mean age of 12 years (49% female). The adults were mostly their mothers, with a mean age of 44 years (87% female). All participants wore a GENEActiv accelerometer on their nondominant wrist for eight consecutive days. The device measured four components of the 24-hour day: sleep duration, sedentary time, light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA).
The researchers used a statistical method called compositional data analysis (CoDA). This method treats the 24-hour day as a whole composition. It recognizes a basic truth: if you increase one activity, you must decrease another. If a child sleeps more, that time comes from somewhere, whether from physical activity, sedentary time or both. The day always adds up to 1440 minutes.
Sleep was measured using Buysse’s sleep health framework, which looks at sleep as more than just duration. The study assessed five dimensions: continuity/efficiency (how much time in bed is actually spent asleep), timing (when sleep starts and ends), alertness/sleepiness (how tired the person feels during the day), satisfaction/quality (how often sleep is troubled) and regularity (how consistent sleep patterns are from night to night).
The key numbers
Children slept an average of 566 minutes per night (about 9.4 hours), with a mean sleep onset at 9:56 PM and offset at 7:23 AM. Sleep efficiency was 84%. Adults slept 498 minutes (about 8.3 hours), with sleep onset at 10:40 PM and offset at 7:03 AM. Sleep efficiency was 86%.
When asked about troubled sleep over the past month, 14% of children reported experiencing it often or always. Among adults, 15% reported the same. About 6% of children and 8% of adults reported feeling quite tired or very tired on the day of assessment.
The counterintuitive finding
The 24-hour activity composition was significantly associated with all measured dimensions of sleep in both children and adults.
The headline result: allocating more time to sleep was associated with less efficient sleep. This was true for both age groups. A modeled increase of 30 minutes in sleep time was associated with a 0.62 percentage point decrease in sleep efficiency for children and a 0.46 percentage point decrease for adults.
The researchers explain this finding in two ways. First, it may reflect a physiological ceiling. The body needs a certain amount of sleep, and spending more time in bed does not automatically translate into more actual sleep. Second, sleep duration in this study was measured as the period between sleep onset and offset, which includes nighttime awakenings. More time in bed may simply mean more time lying awake within that period.
There was an upside to more sleep time: it was associated with more consistent sleep patterns (less night-to-night variability). It was also associated with earlier sleep onsets and later wake times, as would be expected.
Physical activity and sleep quality
The most relevant finding for daily recommendations came from the physical activity data.
In children, all components of the 24-hour activity composition were significantly associated with when the child woke up. Sleep duration and sedentary time were associated with when the child fell asleep, how efficient their sleep was and how variable it was from night to night.
In adults, increasing MVPA (relative to the remaining activities) was the only allocation significantly associated with the subjective dimensions of sleep. Adults who spent more time in MVPA reported less tiredness.
The researchers offer a physiological explanation: engaging in MVPA stimulates the release of serotonin, a neurotransmitter involved in mood regulation and the sleep-wake cycle. Increased serotonin may improve sleep efficiency and reduce tiredness.
The lead researcher, Dr Lisa Matricciani, summarized the practical message in a press release from the University of South Australia: “We found that if children and adults increased moderate to vigorous physical activity, they would feel less tired, have less troubled sleep and better-quality sleep. Interestingly, simply making more time for sleep predicted more restless sleep.”
Sedentary time has its own effects
More sedentary time was associated with more efficient sleep in both children and adults. That may seem like a contradiction, but the researchers point out that an increase in sedentary time necessarily results in shorter sleep duration (when physical activity stays the same), which in turn concentrates sleep into a shorter, more efficient period.
But sedentary time also showed a downside: it was associated with less consistent sleep schedules, later bedtimes and earlier wake times. The paper’s introduction notes that activities like watching television or playing video games that extend into the evening can displace sleep by delaying bedtimes. The study’s results are consistent with that theory, though the sedentary time measured here reflects total daily sedentary time, not evening-specific activity.
Why this study is relevant to child sleep consultants
The children in this study were around 12 years old. That is older than the age range most sleep consultants typically work with. The findings cannot be directly applied to toddlers or preschool-aged children. But the framework behind this study carries relevance for any age group.
The 24-hour day is a fixed container. Every recommendation a sleep consultant makes about bedtime interacts with what fills the rest of the day. When a consultant tells a family to move bedtime 30 minutes earlier, that time has to come from somewhere. This study puts numbers behind that trade-off.
The finding that more time in bed does not automatically improve sleep efficiency is worth raising with parents who believe that the solution to a tired child is always an earlier bedtime. The paper’s clinical implications section states that the 24-hour day “may be constructed in a way to optimize sleep” and suggests that age-specific activity strategies could help address sleep-related issues.
The study also reinforces the role of physical activity as a sleep-supporting behavior. When parents ask what they can do during the day to help their child sleep better at night, this study provides evidence that increasing moderate-to-vigorous physical activity is linked to less tiredness and less troubled sleep.
Limitations
This was a cross-sectional study, so it cannot establish cause and effect. It is possible that people who sleep poorly are less active as a result, rather than the other way around. The adults were predominantly mothers with children aged 11-12, which limits how broadly the findings apply to other adults. The children were all approximately 12 years old. Participants had higher socioeconomic status than the general population. The GENEActiv accelerometer has been validated in adults but not yet in children. Self-report measures of troubled sleep and tiredness were limited to single questions.
The practical message
This 2024 study by Matricciani and colleagues offers sleep consultants a way of thinking about sleep that goes further than bedtime. The 24-hour day is one whole composition, and what happens during waking hours is linked to what happens during sleep. Increasing physical activity during the day is associated with less troubled sleep and less tiredness. Simply adding more time in bed, without changing anything else about the day, is not associated with better sleep quality and may be associated with less efficient sleep.
For sleep consultants, the study provides evidence-backed language for a conversation many already have with families: a good night of sleep starts with an active day.
Matricciani, L., Dumuid, D., Stanford, T., Maher, C., Bennett, P., Bobrovskaya, L., Murphy, A., & Olds, T. (2024). Time use and dimensions of healthy sleep: A cross-sectional study of Australian children and adults. Sleep Health, 10(3), 348–355. https://doi.org/10.1016/j.sleh.2023.10.012