Heatwave disrupts sleep and poses risks, warns researcher

Denmark’s current heatwave is taking a toll on nighttime sleep, with temperatures in some areas reaching 27–29°C in the evenings, far above the 16–19°C range considered optimal for sleep, according to Birgitte Rahbek Kornum, a professor and sleep researcher at the University of Copenhagen’s Institute of Neuroscience.

As global warming intensifies, such extreme heat nights will become more frequent, particularly in southern regions, she told DR. The lack of sleep impairs cognitive function, slows reaction times—raising the risk of traffic accidents—and strains interpersonal relationships.

Elderly individuals are especially vulnerable, as they already experience more unstable sleep patterns. Urban heat islands, where concrete and asphalt retain heat, can further exacerbate nighttime temperatures by up to 2°C in cities like Copenhagen.

Poor sleep from heatwaves, combined with factors like prolonged daylight, alcohol, and caffeine, can have long-term health consequences, including increased risks of cardiovascular disease, dementia, and diabetes, though such effects are less acute in Denmark due to fewer extreme heat events.