Australian and international researchers say sustained extreme heat was linked to an increased risk of heading to the hospital for issues relating to mental health. The researchers looked at hospitalisation records from across the globe, covering over 2.6 million admissions and nearly two decades. With a heatwave being described as being hotter than 97.5% of the other days of the year, and lasting for four consecutive days, the researchers say the relative risk of being hospitalised was around 3.3% higher during the first day of the heatwave, and up to 5.6% higher over the following eight days. These links were stronger among older adults and in people who live in areas with lower population density, the team adds.