Hot Nights Now Cost 48.3 Hours of Sleep a Year, Says the 2026 Lancet Countdown. Living in a Singapore Flat? Apartments Fared 3x Worse

It is 10:30pm in a Singapore flat. Your kid is kicking off the bedsheet for the third time, your partner is pointing the fan at their own side of the bed, and the bedroom still feels warmer than the corridor.

The short answer: the 2026 Lancet Countdown on health and climate change, released on 27 October 2026, estimates that people around the world lost an average of 48.3 hours of sleep a year from 2016 to 2025 because nights were warmer than optimal. A separate Swedish study of 2,209 adults found that apartments, sealed windows and evening heat made the hit worse. That matters if you live in a flat in a hot, humid city.

The new numbers say:

1. 48.3 hours of sleep lost per person each year worldwide (2016 to 2025), 2.9% more than in 2006 to 2015, per the Lancet Countdown.
2. 64 hours a year lost in India from 2021 to 2025, nearly eight full nights, as reported by India Today from the same report.
3. 1.26 vs 0.39 points: how much sleep quality dropped per 1°C of evening bedroom heat in apartments versus small houses in the HeatwiseSweden study, more than three times the drop.

What does the Lancet Countdown actually measure?

The Lancet Countdown tracks dozens of climate and health indicators each year, including sleep lost to hot nights. It does not put sensors in anyone's bedroom. Instead, it applies results from a global study by Kelton Minor and colleagues, published in One Earth in 2022, which linked more than ten billion sleep observations from fitness bands, recorded from 2015 to 2017, to local night temperatures.

The Countdown is open about the limits. Fitness band owners tend to be wealthier than average, and poorer people lose more sleep on warm nights, so the authors say the figure likely underestimates real sleep loss. People may also adapt over time, for example through wider air conditioning use. So treat 48.3 hours as a careful population estimate, not a number about your own bedroom.

Why would a flat sleep worse than a house?

This is where the Swedish data gets useful. The HeatwiseSweden team, writing in the European Journal of Public Health in October 2026, logged bedroom temperature and humidity every 15 minutes for 2,209 adults aged 30 to 85 in six Swedish cities over the summers of 2024 and 2025. Participants rated their sleep quality each day on a 0 to 100 scale, giving 50,735 ratings in total.

Higher indoor temperatures pulled sleep quality down, and the drop sped up as rooms got hotter. The evening window, before sleep, stood out. For every 1°C rise in evening bedroom temperature (between 20°C and 28°C), sleep quality fell by:

| Home setup | Drop per 1°C of evening heat | |---|---| | Apartment | 1.26 points | | Small house | 0.39 points | | Bedroom window can't open | 1.86 points | | Bedroom window opens | 0.81 points | | Mechanical extract ventilation | 0.93 points | | Natural ventilation | 0.42 points | | Noise stops you opening the window | 0.96 points | | Noise doesn't stop you | 0.75 points |

The authors' reading is simple: homes that can't shed heat before bedtime leave sleepers more exposed. Sweden is not Singapore, and these are small shifts on a 100-point scale, but the pattern is familiar. A flat with one bedroom window, road noise outside and the afternoon sun on the wall is the kind of room the study flagged.

Is it the heat or the humidity?

Probably both, and humidity seems to play a smaller but real part. In a SLEEP 2026 conference abstract covering about 24.2 million nights from 201,619 users of under-mattress sleep sensors, each 1°C warmer-than-usual night was linked to a 0.44% lower share of REM sleep and a 0.12% lower share of deep sleep. Each one-point rise in relative humidity was linked to a 0.064% lower REM share and a 0.081% lower deep sleep share. The data came from users of one company's commercial sensors, and an abstract is not a full peer-reviewed paper, so treat it as a signal.

A smaller study of 13 Spanish outdoor workers, tracked daily for a whole summer, found that indoor bedroom temperature was more closely tied to sleep than the weather outside. Each 1°C of indoor heat was linked to 3.18 fewer minutes of sleep, against 2.13 minutes for outdoor heat. Their sleep quality ratings also took less of a hit by August, a hint that people may partly adapt.

What do we know about Singapore bedrooms?

Closer to home, the HEATS project reported in The Straits Times in June 2026 found that bedrooms of 150 Singapore residents averaged 28.4°C at night. That is just above the top of the range where the Swedish study saw sleep quality falling. Across those 150 people, about a third used air conditioning, a third used it on and off with fans, and a third didn't use it at all. A second HEATS study, of construction workers in dormitories without air conditioning, found that each 1°C rise cut sleep by about 10 minutes.

Our earlier post on why Korean mink and fleece blankets backfire in a 28.4°C bedroom looks at bedding choices in that heat, and our post on hot, humid nights and sleep apnoea covers the breathing side.

What can you change tonight?

None of these studies tested a fix, so think of these as low-cost ideas that fit what they found:

1. Cool the room before bed, not after. Evening heat stood out in Sweden, so running the aircon or fan for a while before lights out may help more than switching it on once you're already lying there sweating.
2. Get air moving if the window can't do it. Sealed or noise-blocked windows did worst. A fan pointed across the bed helps the room shed heat.
3. Lighten what's on top of you. A cooling blanket made from breathable fabric traps less heat than fleece. If you like the calm of a weighted blanket, a cooling weighted blanket with a breathable cover is easier to live with in Singapore than a thick, heavy one. Our specifications page lists the fabric and weight details for NightFury, if you want to compare.

If someone at home sleeps badly most nights whatever the temperature, that is worth raising with a doctor.

So in your flat, what's the first thing to go on at night: the aircon, the fan, or the window?

Sources

1. Lancet Countdown 2026. Indicator 1.1.4: Rising night-time temperatures and sleep loss (48.3 hours per year, 2016 to 2025; 2.9% more than 2006 to 2015; caveats) - https://data.lancetcountdown.org/data-explorer/1.1.4-rising-night-time-temperatures-and-sleep-loss
2. The 2026 report of the Lancet Countdown on health and climate change. The Lancet, online 27 Oct 2026 - https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(26)01779-4/abstract
3. India Today. How rising heat is costing Indians nighttime sleep every year (64 hours a year, 2021 to 2025), 4 Nov 2026 - https://www.indiatoday.in/india-today-insight/story/how-rising-heat-is-costing-indians-nighttime-sleep-every-year-3032232-2026-11-04
4. Indoor heat and sleep quality: building and occupant modifiers in the HeatwiseSweden cohort. European Journal of Public Health, Oct 2026 - https://pmc.ncbi.nlm.nih.gov/articles/PMC13698379/
5. Effects of Heat and Humidity on Sleep Parameters: Insights from 24.2 Million Nights Using an Under-Mattress Sleep Monitoring Device. SLEEP 2026 abstract 1270 - https://doi.org/10.1093/sleep/zsag091.1269
6. Montanari A et al. Time-varying associations of temperature and sleep as a marker of heat adaptation: Spanish outdoor workers. The Journal of Climate Change and Health, 2026 - https://pmc.ncbi.nlm.nih.gov/articles/PMC13691138/
7. Minor K et al. Rising temperatures erode human sleep globally. One Earth, 2022 - https://www.cell.com/one-earth/fulltext/S2590-3322(22)00209-3
8. Shabana Begum, The Straits Times, 25 Jun 2026. Project HEATS: 150 Singapore residents' bedrooms average 28.4°C at night - https://www.straitstimes.com/singapore/environment/whats-the-temperature-in-the-bedroom-in-spore-a-muggy-28-deg-c-says-new-study-on-residents