You know the feeling, you wake up feeling groggy, tired, irritable, almost like you have a hangover.
In Australia temperatures like last week’s heatwave – which saw suburbs stay at around 30 degrees Celsius overnight – and with hot days expected throughout the southern summer, sleep disruption is going to be a regular pain in the neck.
While the body’s core temperature generally hovers steadily around 37C, there is a potential for it to rise and develop into a fever if the surface temperature cannot be cooled and a room remains hot ::::
Sleep expert David Hillman explained why our bodies struggled to sleep soundlessly during those hot nights.
“Once you get through the mid-20s you’ve gone through the thermo-neutral zone,” Hillman said. “Your body is having to do some active things to get rid of the heat it’s generating.”
The thermo-neutral zone is when the body is at equilibrium with the outside temperature. The average core body temperature is 37C and it is most comfortable when the temperature of the environment is at 24C.
Any higher and the body starts feeling uncomfortable and has to work harder to regulate itself.
“The blood vessels near the surface of the body dilate, get bigger so more blood is going through the surface of the body and you start to sweat to help keep the temperature down,” Mr Hillman said.
“Even when you’re lying still in bed asleep, it’s making energy … the equivalent of a 100-watt lightbulb, those temperature needs to be eliminated. If there are things the body thinks is threatening it’s going to rouse you.” Hillman said. “If sleep is disrupted enough, you get into this sleep-restricted state and things don’t work as well.”
Mr Hillman, the chairman of the Sleep Health Foundation, said lack of sleep led to problems with thinking clearly and slower reaction times and mood is also affected.
While the body’s core temperature usually remains steady at 37C, there is a potential for it to rise and develop into a fever if the surface temperature cannot be cooled and a room remains hot.
According to Dr Liz Hanna from the College of Biology, Medicine and Environment at the Australian National University, there was a risk of “accumulated heat burden” particularly on consecutive hot days and nights.
“One of the things that make a heatwave dangerous … particularly if we can’t cool down overnight, is that heat load carries over,” Dr Hanna said. “That discomfort is not only fatiguing but people get grumpy.”
Dr Hanna suggested people set a bucket of water beside their bed to regularly wet a towel throughout the night.
“I wet a face washer or hand towel and drape it over myself and turn on the fan,” Mr Hillman said, “…the combination of moisture from the wet towel and evaporation via the fan helped lower the body’s surface temperature and cool down.”
His other tip for getting through a hot night was to use cotton bed linen and pyjamas “so that you’ve got skin exposed”. He also recommended that a fan was used to “get the air moving”, while those with partners should stick to their own sides of the bed. A hot night is not a time for cuddles.”