The study was led by Dr. Fergus O’Connor from Griffith’s School of Allied Health, Sport and Social Work. His research focused on how higher nighttime bedroom temperatures influence heart rate and stress levels in older people.

“For individuals aged 65 years and over, maintaining overnight bedroom temperatures at 24°C reduced the likelihood of experiencing heightened stress responses during sleep,” Dr. O’Connor said.

Why Heat Increases Stress on the Body

Dr. O’Connor explained that heat places extra demands on the cardiovascular system.

“When the human body is exposed to heat, its normal physiological response is to increase the heart rate. The heart is working harder to try and circulate blood to the skin surface for cooling.

“However, when the heart works harder and for longer, it creates stress and limits our capacity to recover from the previous day’s heat exposure.”

Tracking Sleep in Real-World Conditions

Participants in the study wore fitness activity trackers on their non-dominant wrist to record heart-related data during sleep. At the same time, temperature sensors installed in their bedrooms continuously measured overnight conditions throughout the Australian summer-long data collection period.

The results provided the first real-world evidence showing how higher bedroom temperatures directly affect heart rate and stress responses during sleep.

Hot Nights, Climate Change, and Health Risks

According to Dr. O’Connor, the findings are especially relevant as nighttime temperatures continue to rise. “Climate change is increasing the frequency of hot nights, which may independently contribute to cardiovascular morbidity and mortality by impairing sleep and autonomic recovery,” he said.

He also noted an important gap in existing guidance. “While there are guidelines for maximum daytime indoor temperature, 26°C, there are no equivalent recommendations for nighttime conditions.”

The research paper, ‘Effect of nighttime bedroom temperature on heart rate variability in older adults: an observational study’, has been published in BMC Medicine.