Rising night temperatures threaten sleep and health, researchers warn

Record-breaking night-time heat in cities from Delhi to France and the US Gulf Coast has exposed a growing public-health issue: insufficient cooling during sleep. Surveys in the United Kingdom reveal that most people experienced sleep difficulties during recent heatwaves, and analyses of over 1,300 cities estimate an average loss of nearly 56 sleep hours per resident each year. Research across East Asian urban areas links hot nights to a 3% increase in mortality and higher emergency admissions, especially among older and low-income residents.

Scientists say that measuring only outdoor temperature fails to capture the true physiological strain, recommending the use of bedroom sensors, wearables, and health data to assess recovery. They propose five research priorities, including defining a “recoverable night” and evaluating cooling interventions based on sleep quality rather than temperature alone. Such efforts aim to inform policies that ensure nights remain cool enough for restorative sleep as climate change intensifies.