What happens to a child’s sleep when 174 people share one room on a summer night? A 2024 study from Japan measured it, down to the temperature between each child’s body and their bedding. The results were severe.
The study, titled “How staying in a gymnasium affects sleep and bed climate in children,” was published in the Journal of Physiological Anthropology by Okamoto-Mizuno and Mizuno. The researchers tracked sleep, room conditions and bed-level temperature in 13 school-aged children during a one-night stay in a school gymnasium used as a simulated emergency shelter. They compared that night with normal sleep at home. The aim was to understand which thermal factors in a shelter environment affect children’s sleep, and how.
Who took part
The 13 children (6 boys, 7 girls) had a mean age of 11.4 years. They were healthy fifth- and sixth-graders from one elementary school. The one-night stay was part of a summer camp. In total, 174 people slept in the gymnasium that night: 123 children, 45 parents and 6 teachers. The floor area was approximately 1050 m².
Each child wore a wrist actigraph for seven consecutive days: three days before the camp night (BC), the camp night itself (C) and three days after (A1 and A2). This gave the researchers a clear comparison between sleep in the gymnasium and normal sleep at home.
Every child in the gymnasium received the same sleeping bag (polyester, 1.1 kg) and the same thin underside mattress (1800 mm × 600 mm × 8 mm). At home, children used their usual mattress or futon with a cover.
What happened to their sleep
Sleep efficiency dropped to 43% (± 4.8%) on the camp night. This was significantly lower than every other condition. At home, the children slept normally.
Total sleep time was significantly shorter in the gymnasium. Sleep latency was significantly longer. The children woke more often, stayed awake for longer stretches, and moved more during the night. The longest episode of being awake was significantly longer than on any home night.
The disruption was concentrated in the first 195 minutes after lights out. In every 15-minute interval during that initial period, sleep time was significantly lower in the gymnasium. After 195 minutes, no significant differences remained.
The next day (A1), the children slept significantly more during the daytime than on any other day, suggesting their bodies were compensating for lost sleep.
What the children reported
When asked what disturbed their sleep, 10 out of 13 children (77%) said heat. Other reported factors included noise, a hard floor, a small sleeping space and collisions with other people. None of the children reported anxiety.
Subjective assessments before sleep confirmed this: the children rated the gymnasium as significantly hotter than home on the pre-camp night (BC). Sweat and humidity sensations before sleep were also significantly higher in the gymnasium than at home.
The subjective assessment of overall sleep quality was significantly worse on the camp night than on all home nights, and the children rated sleep onset as significantly more difficult.
The ambient climate inside the gymnasium
The researchers measured room temperature and humidity continuously throughout the night, both in the gymnasium and in the children’s bedrooms at home.
The gymnasium temperature started at 26.7°C and gradually fell to 25°C over the course of the night. During the first 180 minutes, it was significantly higher than the pre-camp home bedroom temperature (BC). In the last 100 minutes, it dropped and was significantly lower than the post-camp home nights (A1 and A2), which were warmer nights overall.
The humidity in the gymnasium was significantly higher than on the post-camp nights (A1 and A2). The researchers noted that high ambient temperature combined with high humidity during the initial sleep segment may have increased heat stress for the children.
The gymnasium’s temperature was more affected by outdoor weather than the children’s bedrooms at home. The researchers attributed this to the building’s construction: the floor of a gymnasium is typically exposed to outside air, with less insulation than a home. Outside temperatures had risen by about 6°C during the day and 2°C at night between BC and C.
Based on these findings and their previous research on children in gymnasium settings, the researchers suggest that the ambient temperature should be kept below 26°C during the first segment of sleep when a large number of people are staying in a gymnasium.
The bed climate: a separate measurement
The researchers also measured something distinct from room temperature: the bed climate. This is the microclimate between the body and whatever covers it. Small sensors were attached to the outer layer of the children’s clothing at the chest and at the foot, recording temperature and humidity every minute.
Previous research cited in the paper reports that during normal sleep, the bed climate temperature in the waist area is generally maintained at around 32-34°C with 40-60% relative humidity. For school-aged children, the foot area during normal summer and autumn sleep is maintained at 28-30°C with 50-70% relative humidity.
On the camp night, the bed climate temperature of the chest area was significantly lower than on the two post-camp home nights (A1 and A2). The increase in chest bed climate temperature was significantly delayed in the gymnasium compared to all other conditions during the first 15 to 30 minutes after lights out.
The foot area showed a similar pattern. The bed climate temperature of the foot was significantly lower in both BC and C compared to A1. The temperature increase at the foot was also significantly delayed in the gymnasium compared to other conditions during the first 5 to 15 minutes.
Why was the bed climate temperature delayed? The researchers point to how the children used their sleeping bags. At sleep onset, only 15% of the children were inside their sleeping bag. The rest were either not using it at all or had placed it under their body as padding. Without the insulating layer of the sleeping bag around them, the bed climate temperature at the chest could not build up the way it would under normal bedding at home.
As the gymnasium cooled during the later part of the night, more children got into their sleeping bags. By the time they woke up, 50% were inside. This change coincided with the period after 195 minutes, when sleep disturbance was no longer significant.
What the researchers concluded
The paper’s conclusion is careful. It states that the disturbed sleep observed in the gymnasium “may be related to” the delayed increase in bed climate temperature at the chest. It adds that this delayed increase “could be related to” the children not entering the sleeping bag and a delayed chest skin temperature increase during the sleep onset period.
The researchers do not claim that bed climate was the only factor or the main factor. Their discussion notes that the decreased sleep during the first 195 minutes “may include not only ambient climate but other factors such as the first night effect, the effect of noise, and hard floors.” They also note that the improvement after 195 minutes may relate to decreased ambient temperature, increased sleep pressure, decreased noise levels, or a combination of these.
The paper’s stated purpose is to inform practical applications for disaster prevention. It builds on the authors’ previous studies of children sleeping in Japanese gymnasium shelters and is specifically aimed at understanding which thermal factors in shelter environments affect children’s sleep.
What sleep consultants can take from this
This study was not designed for home sleep settings! It studied 11-year-olds in a gymnasium with 174 people, hard floors, noise averaging 44 dB with peaks up to 77.5 dB, and no air conditioning. These conditions are far removed from a typical bedroom.
But the study introduces a concept that sleep consultants rarely encounter in the research: bed climate. The idea that the temperature between the child’s body and the bedding is a separate and measurable factor, distinct from room temperature, is useful to know about. The paper’s data shows that on the camp night, the room was warm but the bed climate at the chest was delayed in reaching its normal range, and sleep was disrupted during that same period.
The study also documents what happens when children are too hot to get under covers. In the gymnasium, 85% of the children did not enter their sleeping bags at the start of the night. The paper suggests this contributed to the delayed bed climate temperature at the chest. Whether a similar pattern occurs in home settings, where children kick off blankets or refuse to stay under covers on warm nights, is a question the paper does not answer. It would require separate research.
Limitations
This was a small study with 13 children from one school in Japan during a single summer night. The gymnasium environment involved many disrupting factors that cannot be separated from one another: heat, humidity, noise, a hard floor, thin mattresses, standardized sleeping bags, crowding and the first-night effect. The actigraph-based sleep analysis may differ from polysomnography. Bed climate sensors were placed on the outer layer of clothing, not directly on the skin. The findings are specific to shelter conditions and cannot be directly applied to normal home sleeping environments.
Okamoto-Mizuno, K., & Mizuno, K. (2024). How staying in a gymnasium affects sleep and bed climate in children. Journal of Physiological Anthropology, 43, 2. https://doi.org/10.1186/s40101-023-00350-3