In late January, the South Australian city of Adelaide endured its hottest night on record, with thermometers still measuring temperatures of 34.1 degrees Celsius (about 93 degrees Fahrenheit) just before 7 am. Such sweltering nighttime conditions have long been linked to a greater risk of hospitalization for everything from cardiovascular to mental health conditions. “We started wondering whether some of this could be explained by loss of sleep or poor quality sleep,” says Bastien Lechat, a scientist leading a research program on sleep health at Flinders University. Sleep apnea is already estimated to impact around a billion people around the world, many of whom are unaware they have the condition. High temperatures impair the body’s ability to cool down at night, meaning that sleep is lighter and more fragmented, and sleep apnea events tend to occur more during light rather than deep sleep.