Regulating temperatures while sleeping could help to reduce stress on the body and heart for older people, new research has found. 

The study by Griffith University researchers and published in the BMC Medicine journal found that keeping room temperatures at 24 degrees Celsius or below reduced participants' heart rate variability (HRV) and decreased physiological stress.

Participants wore health monitoring devices provided by researchers to record their physiological status throughout last summer — December 2024 to March 2025.

Researcher Fergus O'Connor said the study surveyed 47 people aged 65 and over, as far south as Coolangatta and as far north as the mid-north Sunshine Coast. 

Participants who slept at temperatures above 24C are more likely to be in "fight or flight" mode while sleeping. (ABC News: Kate Nickels)

"What we saw was with increasing overnight bedroom temperatures — so the sleeping environment — greater stress responses were evident and, in turn, individuals were recovering less," Dr O'Connor said.

He said participants who slept at temperatures above 24C were more likely to be in a sort of "fight or flight" mode while sleeping.

"When it gets above 24 degrees … particularly up towards 28 or 30C, physiologically there's a requirement for the body to try to lose heat.

"So the individual is not resting and recovering."

There was no set temperature when heat stress became immediately dangerous, but Dr O'Connor said outcomes tended to get worse as temperatures increased. 

Senior researcher at the University of Sydney, Georgia Chaseling, said the study helped confirm previously held notions about the effect of hot sleeping environments on heart rate response. 

"We already know a little bit that when there are hotter nights, they're linked to changes in heart rate patterns and heart rate variabilities," Dr Chaseling said. 

"My takeaway from this is that this study is showing an association between hot weather and changes in heart rate variability, but it's not necessarily showing that hot weather causes changes or decreases in heart rate variability."

Georgia Chaseling says the heart rate increases to try to regulate body temperatures as the environment gets warmer. (Getty Images)

She said future research should work to pin down the relationship between sleeping temperatures and stress reactions by controlling more strongly for variations in daily activity and across a broader sample group and climate areas.