Observational study finds higher bedroom temperatures increase autonomic disruption in older adults — Evidence Review
Published in BMC Medicine, by researchers from Griffith University
Researched by
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Table of Contents
Older adults may benefit from keeping their bedrooms at or below 24°C (75°F) during sleep to reduce stress on the heart, according to a new Griffith University study tracking real-world conditions. This finding aligns with broader research showing that indoor temperature can affect cardiovascular and autonomic health.
- Large-scale reviews consistently link higher temperatures—both indoors and outdoors—to increased cardiovascular risk, particularly in older adults, supporting the importance of temperature regulation for heart health 1 2 5 13.
- Prior studies have identified temperature thresholds (often around 26°C) above which health risks increase, especially for vulnerable groups, while the new study suggests benefits at even cooler nighttime temperatures 2 5.
- Research on autonomic function and sleep also supports the new findings, as disrupted or poor-quality sleep is associated with increased sympathetic activity and cardiovascular strain [6–10].
Study Overview and Key Findings
As global temperatures rise and heatwaves become more common, the health impacts of warm indoor environments—especially at night—are under growing scrutiny. Older adults are particularly vulnerable to heat-related stress, yet there has been limited real-world evidence on how bedroom temperatures during sleep affect physiological recovery. This new study addresses that gap by monitoring older adults in their own homes throughout an Australian summer, using wearable devices and environmental sensors to link bedroom temperature with cardiac autonomic responses during sleep.
| Property | Value |
|---|---|
| Study Year | 2025 |
| Organization | Griffith University |
| Journal Name | BMC Medicine |
| Authors | Fergus K. O’Connor, Aaron J. E. Bach, Connor Forbes, Shannon Rutherford, Sebastian Binnewies, Surendran Sabapathy, Norman R. Morris |
| Population | Older adults |
| Sample Size | n=47 |
| Methods | Observational Study |
| Outcome | Heart rate variability, stress-related autonomic responses |
| Results | Higher bedroom temperatures increased odds of autonomic disruption. |
In this in-home observational study, 47 community-dwelling adults aged 65 and over in southeast Queensland, Australia, were monitored during summer nights. Participants wore wrist-worn activity trackers while bedroom temperatures were logged every 10 minutes. Analysis focused on sleep periods (9 PM – 7 AM) and assessed heart rate variability (HRV) as a marker of autonomic (stress) response.
Key findings include:
- Median bedroom temperature was 25.9°C (78.6°F), with many participants exposed to temperatures above the 24°C threshold.
- Nights spent in warmer bedrooms were associated with stepwise increases in the odds of clinically meaningful reductions in HRV, a sign of impaired autonomic recovery.
- HRV parameters indicated increased sympathetic (“fight-or-flight”) dominance and diminished parasympathetic (“rest-and-digest”) activity as temperatures rose, suggesting increased physiological strain.
- The study underscores the potential value of setting nighttime bedroom temperatures at or below 24°C for older adults to support cardiovascular recovery during sleep.
Literature Review: Related Studies
To situate these findings, we searched the Consensus research database—containing over 200 million papers—using the following queries:
- bedroom temperature heart health
- autonomic disruption sleep environment
- thermal comfort cardiovascular outcomes
Below, we summarize major themes and findings from the literature:
| Topic | Key Findings |
|---|---|
| How do indoor temperatures affect cardiovascular and autonomic health in older adults? | - Higher indoor and ambient temperatures correlate with increased cardiovascular morbidity and mortality, especially for those over 65 1 13. - Indoor temperatures above 26°C are associated with adverse health effects, particularly in vulnerable populations 2 5. |
| What temperature thresholds are linked to health risks or benefits indoors? | - Research suggests indoor temperatures above 26°C increase risk for respiratory, cardiovascular, and cognitive issues in at-risk groups 2. - Summer indoor temperatures of 20–23°C are recommended for comfort and health; exceeding 26°C may be harmful for patients with respiratory or cardiovascular conditions 5. |
| How does sleep environment temperature impact autonomic function and recovery? | - Poor sleep quality and short sleep duration are associated with reduced parasympathetic activity and greater sympathetic dominance, increasing cardiovascular risk [6–10]. - Heart rate variability (HRV) is a sensitive marker of thermal comfort and autonomic balance, with higher LF/HF ratios (sympathetic activity) occurring in thermally uncomfortable environments 12. |
| Are there health risks related to cold indoor environments for older adults? | - Prolonged exposure to cold indoor temperatures (<18°C) is also linked to negative cardiovascular and general health outcomes, particularly in older adults 4. - Intensive heating in winter can lower morning blood pressure and blunt blood pressure surges, providing cardiovascular benefit 3. |
How do indoor temperatures affect cardiovascular and autonomic health in older adults?
Research consistently demonstrates that both high ambient and indoor temperatures are associated with increased risk of cardiovascular events and mortality, particularly in older adults. The new study’s focus on nighttime bedroom temperatures extends these findings by highlighting the importance of recovery periods—such as sleep—for minimizing heat-related physiological strain in this population 1 13.
- Older adults are more susceptible to heat-induced cardiovascular events, making temperature regulation especially important for this group 1.
- Systematic reviews show that even a 1°C rise in temperature can increase cardiovascular morbidity and mortality among those 65 and older 1.
- Indoor temperatures above 26°C have been linked to adverse health outcomes in at-risk populations, including older adults 2.
- The new findings reinforce the need for clear indoor temperature guidelines for vulnerable populations during both daytime and nighttime hours 2 5.
What temperature thresholds are linked to health risks or benefits indoors?
Several studies have attempted to define safe indoor temperature ranges. While 26°C is often cited as an upper limit for at-risk groups, recent reviews suggest that the optimal range for health may be even lower, particularly in summer, and that thresholds for negative health effects can vary depending on specific health conditions 2 5.
- Indoor temperatures above 26°C are associated with increased respiratory distress, exacerbation of chronic diseases, and cognitive symptoms in vulnerable groups 2.
- For cardiovascular health, summer indoor temperatures of 20–23°C are considered optimal, with risks increasing above 26°C 5.
- The new study suggests that keeping bedrooms at or below 24°C may provide additional benefit for autonomic recovery, indicating that current guidelines might not be sufficiently protective, especially for nighttime conditions 5.
- There is a lack of nighttime-specific temperature recommendations, which the new study helps to address 2 5.
How does sleep environment temperature impact autonomic function and recovery?
Thermal environment during sleep affects autonomic nervous system activity. Disrupted or insufficient sleep, often worsened by uncomfortable temperatures, is associated with increased sympathetic (stress-related) activity and decreased parasympathetic (restorative) activity, which can elevate cardiovascular risk [6–10,12].
- Short sleep duration and poor sleep quality consistently correlate with lower HRV and higher sympathetic tone, both risk factors for cardiovascular disease [6–8].
- HRV indices, such as the LF/HF ratio, have been validated as markers of thermal discomfort and autonomic imbalance under different environmental conditions 12.
- The new study’s use of HRV to measure stress responses during sleep adds real-world evidence that hotter bedroom environments can impair overnight autonomic recovery 7 8 12.
- These findings support broader links between sleep environment, autonomic function, and cardiovascular health [6–10].
Are there health risks related to cold indoor environments for older adults?
While the focus is often on heat, cold indoor temperatures also pose significant risks, particularly for older adults. Research shows that maintaining indoor temperatures above 18°C is important for preventing cardiovascular and other health issues during colder months 3 4.
- Cold indoor temperatures (<18°C) are linked to elevated blood pressure, increased cardiovascular risk, and worsened respiratory symptoms in older adults 4.
- Intensive room heating during winter can reduce morning blood pressure surges, supporting cardiovascular health 3.
- Balancing the risks of both excessive heat and cold is necessary for protecting vulnerable populations year-round 3 4.
- The new study’s emphasis on optimal summer bedroom temperatures complements existing research on winter indoor environment and health 3 4.
Future Research Questions
Despite growing evidence on the health impacts of indoor temperatures, important knowledge gaps remain. Future research should clarify optimal temperature ranges for different populations, mechanisms underlying temperature-related cardiovascular risk, and effective interventions to protect vulnerable groups as global temperatures rise.
| Research Question | Relevance |
|---|---|
| What is the optimal nighttime bedroom temperature for cardiovascular recovery in older adults? | Determining precise temperature thresholds can inform public health guidelines and interventions to reduce cardiovascular risk in aging populations 2 5. |
| How do fluctuations in nighttime temperature (rather than average temperature) affect autonomic function? | Understanding the impact of temperature variability could help identify critical periods of risk and inform strategies for indoor climate management 2 12. |
| What are the long-term health consequences of chronic exposure to warm bedroom environments in older adults? | Most studies focus on short-term or acute exposures; longitudinal research is needed to assess cumulative effects on cardiovascular and cognitive health 1 5. |
| Can targeted interventions (such as cooling devices or behavioral changes) effectively mitigate autonomic disruption in hot bedrooms? | Evaluating the effectiveness of practical interventions could help protect at-risk groups in the context of climate change and rising nighttime temperatures 1 2. |
| How do indoor temperature effects interact with other factors such as humidity, air quality, and sleep disorders? | Multifactorial studies could reveal combined or synergistic effects on cardiovascular and autonomic health, improving risk assessment and guidance 5 6 8. |
As the climate changes and the global population ages, addressing these questions will be critical for developing evidence-based recommendations to protect cardiovascular health—particularly for those most vulnerable to environmental stressors during sleep.