Higher bedroom temperatures are associated with lower heart rate variability and higher heart rate during sleep. Digest
Climate projections suggest hot nights may contribute more to heat-related deaths than hot days in the future, yet healthy indoor nighttime temperature thresholds remain undefined. To address this gap, researchers tracked older adults in their own homes across summer, pairing bedroom temperature with wearable measures of cardiovascular strain during sleep.
You just missed this in your inbox
Every other week our Premium Members received this exact study plus Rhonda's practical commentary and 8+ other hand-picked papers.
Researchers monitored 47 community-dwelling adults aged 65 years and older in southeast Queensland, Australia, from December 2024 to March 2025. Participants wore a wrist device that used photoplethysmography (a light-based method that measures tiny changes in the amount of blood in the skin) to derive heart rate and heart rate variability (HRV). In-home sensors continuously measured bedroom temperature, and analyses focused on nighttime sleep hours, 9 PM to 7 AM, comparing temperature categories and clinically meaningful changes in physiology.
- Compared with nights below 24°C (75.2°F), warmer bedrooms were linked to reductions in a measure of HRV that reflects the small changes in the timing between one heartbeat and the next. At 28 to 32°C (82.4 to 89.6°F), participants were nearly three times more likely to show this reduction.
- The decline was not limited to these beat-to-beat changes. It also affected the repeating rises and falls in heart rate that unfold over several seconds and can be separated into a faster component reflective of parasympathetic ("rest-and-digest") activity of the heart and a slower component.
- The researchers compared these repeating slower and faster fluctuations by taking their ratio. This ratio rose at higher temperatures, a pattern often interpreted as greater sympathetic ("fight-or-flight") influence, although that interpretation remains debated.
- Sleep heart rate increased as bedrooms warmed. At 28 to 32°C (82.4 to 89.6°F), participants were nearly four times more likely to experience an increase of at least 5 beats per minute during sleep compared with nights below 24°C (75.2°F).
These results might relate to thermoregulation, the body's process for maintaining a stable internal temperature. Heat exposure increases skin blood flow to facilitate cooling, which raises cardiac workload and can elevate heart rate. Elevated nighttime temperatures may also promote oxidative damage to blood vessels and trigger systemic inflammatory responses, potentially disrupting autonomic function (the automatic regulation of vital processes by the autonomic nervous system through its sympathetic and parasympathetic branches). Taken together, the observed heart rate patterns are consistent with a shift toward sympathetic dominance and heightened physiological stress.
The study included a relatively small sample from a single subtropical region, and it was observational, meaning it cannot prove causation. Still, the findings suggest that keeping bedrooms cooler than 24°C (75.2°F) at night could represent a practical strategy to help reduce cardiovascular strain in older adults. In episode #107, renowned sleep expert Dr. Michael Grandner explains how to overcome insomnia and use sleep to optimize health.