Is Your Bedroom Air Quietly Costing You Deep Sleep?

Possibly, a little. In a Shanghai dormitory study published in Scientific Reports, students whose bedrooms had more fine particles (PM2.5) overnight spent a smaller share of the night in deep sleep and ran worse in their fitness test the next morning. The finding got fresh coverage this week, including an 8 October write-up from The Water Room. It is one observational study of healthy 18 to 22 year olds, so treat it as a prompt to check your own bedroom air, not a verdict. It matters in a city like Singapore, where many people sleep in closed, air-conditioned rooms.

What did the Shanghai study measure?

A team from Shanghai Jiao Tong University put sensors beside students' beds for one night before the school's standard fitness test. They tracked PM2.5, CO2, air temperature and relative humidity. Sleep was estimated with a wrist-worn Fitbit Alta HR, which the authors note is less precise for sleep stages than clinical polysomnography. The next morning, students did a 1,000 m run (men) or 800 m run (women), plus sprints, jumps, sit-ups and pull-ups.

183 students were recruited and 163 had valid data. The dorms had no mechanical ventilation, and no fans or air-conditioning were used. Average bedroom conditions were 21.3 °C, 62% humidity, 1,437 ppm CO2 and 16 µg/m³ PM2.5.

What did they find?

| Bedroom factor | Linked to | Size (standardized) | | --- | --- | --- | | Higher PM2.5 | Lower share of deep sleep | β = -0.19 | | Higher PM2.5 | Worse long-distance run score | β = -0.34 | | Higher CO2 | More light sleep | β = 0.17 | | High CO2 (3,961 ppm vs 445 ppm) | Stronger PM2.5 and running link | interaction p = 0.03 | | Humidity | Best run scores near 62%, worse at lower or higher | quadratic, p = 0.01 |

Sprints, jumps, sit-ups and pull-ups showed no significant link to any bedroom factor. The authors also tested whether sleep explained the running result and found no significant mediation. So the data does not show that dirty air hurt running by way of poorer sleep.

How strong is this?

Modest. The standardized effects are small to moderate, the models explain roughly 10% to 35% of the variation, and the authors say the findings need cautious reading. Other caveats:

• One night per student, so no sense of habitual exposure.
• Young, healthy undergraduates in similar dorms, spring and autumn weather, bedroom temperatures roughly 16 to 26 °C. That is not a tropical night.
• The humidity result is the weakest to act on. The best-performing humidity sat right at the sample average of 62%, and the authors call for lab studies to confirm it. It also concerns running, not sleep.
• Particles, CO2 and humidity were not manipulated. This is association only.

Is there evidence that fresher air improves sleep?

A separate line of research tested it directly. In two field experiments by Technical University of Denmark researchers in student bedrooms (14 and 16 people), each person slept a week under each of two ventilation setups. With an open window, average CO2 was about 660 ppm versus 2,585 ppm. In the second experiment, a quiet fan kept CO2 near 835 ppm versus 2,395 ppm without it. Lower CO2 went with better actigraphy-measured sleep, fresher perceived air, less next-day sleepiness, better self-reported concentration and a better score on a logical thinking test. Samples were small, but the design was a crossover, which makes it a useful companion to the Shanghai data.

What does this mean for Singapore bedrooms?

The honest answer is that nobody has published this exact test in Singapore homes. But the pieces are familiar. If you sleep with the door and windows shut and the AC on, the air in the room can get stale overnight, since two people breathing in a small room add CO2 for 7 to 8 hours.

For a rough yardstick, Singapore's NEA advises keeping CO2 below 800 ppm in enclosed air-conditioned premises such as clinics and gyms, and the national indoor air standard SS 554:2026 caps it at 700 ppm above outdoor levels, roughly 1,100 ppm. Those apply to commercial premises, not homes, but the Shanghai dorm average of 1,437 ppm would be well above both.

WHO's 2021 guideline for PM2.5 is 15 µg/m³ as a 24-hour average (5 µg/m³ yearly). That is an outdoor air guideline, not a bedroom rule, but it gives context for the 16 µg/m³ average bedroom reading in this study.

What can you try tonight?

• Measure first. A basic NDIR CO2 meter shows whether your room climbs well past the 800 ppm yardstick overnight. Keep it at least half a metre from your face.
• Let air move. Crack a door or use a window gap when outdoor air is clean, or run a quiet fan or exhaust. Skip this on hazy days.
• Filter particles. Air filters can reduce fine particles, though a noisy unit or a cold draft can cost you sleep of its own.
• Treat heat as its own lever. Air quality is one factor. A cooling weighted blanket with breathable fabric addresses warmth and pressure, not CO2 or particles, so you can still work on the air separately. The specifications page lists what that blanket design does and does not do. A weighted blanket is a personal pick, so try it for a few nights before judging.
• Do not chase 62% humidity. The evidence is too thin to set a target.

If you struggle to sleep for weeks, speak with a clinician.

Sources

1. Lin X, Ji T, Guo R, Guo C, Gong P, Lan L. "Association of bedroom particulate matter, sleep quality and next-day physical performance." Scientific Reports 16:7117, 2026 (published 3 Feb 2026). DOI: https://doi.org/10.1038/s41598-026-37949-2 (full text: https://www.nature.com/articles/s41598-026-37949-2)
2. Ellwood H. "Bedroom Air Pollution Linked to Deep Sleep and Next-Day Running Performance." The Water Room, 8 Oct 2026: https://thewaterroom.co.uk/8-705518038-bedroom-air-pollution-linked-to-deep-sleep-and-next-day-running-performance/
3. Strøm-Tejsen P, Zukowska D, Wargocki P, Wyon DP. "The effects of bedroom air quality on sleep and next-day performance." Indoor Air 26(5):679-686, 2016. DOI: https://doi.org/10.1111/ina.12254 (PubMed: https://pubmed.ncbi.nlm.nih.gov/26452168/)
4. World Health Organization. "WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide," 2021. Executive summary with PM2.5 table: https://pmc.ncbi.nlm.nih.gov/articles/PMC12052406/ (WHO overview: https://www.who.int/news-room/questions-and-answers/item/who-global-air-quality-guidelines)
5. National Environment Agency Singapore. "Advisory on CO2 Monitoring to Assess Ventilation Adequacy" (first released June 2022, updated April 2026): https://www.nea.gov.sg/our-services/public-cleanliness/environmental-cleaning-guidelines/advisories/advisory-on-co2-monitoring-to-assess-ventilation-adequacy