Is your bedroom too warm for your ageing heart? New study raises alarm

Hot nights may be stressing ageing hearts. A new Australian study finds that bedroom temperatures above 24 degrees Celsius during sleep can disrupt heart recovery in older adults

The temperature of your bedroom at night could be affecting your heart. A new study suggests that sleeping in a warm room may interfere with the heart’s ability to rest and recover, especially in older adults.

 

The study, Effect of nighttime bedroom temperature on heart rate variability in older adults: an observational study, published in BMC Medicine, tracked older adults through an entire summer in south-east Queensland, Australia, and found that bedroom temperatures above 24 degrees Celsius were linked to signs of increased heart stress during sleep.

 

Forty-seven older adults, aged 65 and above, were monitored over nearly four months. They wore fitness trackers that continuously recorded heart rate and heart rate variability (HRV) during sleep, while sensors measured bedroom temperature every 10 minutes. This allowed scientists to see how the heart responded to heat during normal, everyday sleep at home.

 

Why bedroom temperature during sleep matters for heart health

When the body gets too warm, it works harder to cool itself. Blood is pushed towards the skin, and the heart beats faster to help release heat. While this response is normal, it becomes a problem if it continues for hours during sleep.

 

Sleep is meant to be a recovery window for the heart. If heart rate remains elevated and stress signals persist overnight, the body may not fully recover from the day’s strain. Over time, this reduced recovery could increase cardiovascular risk, particularly in older adults who are already more vulnerable to heat. 

What heart rate variability reveals about overnight heart recovery

Heart rate variability refers to the small, natural variations in time between heartbeats. Higher HRV generally indicates that the heart is flexible and well-regulated, with strong “rest-and-digest” nervous system activity. Lower HRV suggests the body is under stress and leaning towards a “fight-or-flight” state.

 

In this study, lower HRV during sleep was used as a marker of physiological strain. Consistently reduced HRV at night signals that the heart and nervous system are not recovering as they should.

What the study found about heat and heart stress during sleep

According to the study, the median bedroom temperature during sleep was 25.9 degrees Celsius, already above the level associated with healthier heart recovery. As bedroom temperatures rose, so did signs of cardiac stress.

 

Compared with sleeping in rooms cooler than 24 degrees Celsius, the likelihood of clinically meaningful drops in HRV increased step by step. Bedrooms at 24–26 degrees Celsius raised the odds modestly, but at 26–28 degrees Celsius the risk roughly doubled. At 28–32 degrees Celsius, the odds of heart stress were nearly three times higher.

 

Higher temperatures were also linked to faster heart rates and patterns suggesting greater dominance of stress-related nervous system activity during sleep.

Is 24 degrees Celsius a meaningful threshold for heart health?

The study does not claim that 24 degrees Celsius is a perfect cut-off, but it highlights it as a meaningful threshold. Below this level, the heart showed fewer signs of strain. Above it, the body increasingly struggled to maintain normal overnight recovery.

 

Notably, while there are global guidelines for maximum daytime indoor temperatures, often set around 26 degrees Celsius, there are currently no formal recommendations for night-time bedroom temperatures. This research adds real-world physiological evidence to support the idea that nights need their own heat guidelines.

 

For older adults, especially those with heart conditions, diabetes, or on certain medications, night-time heat may be a hidden health risk. Simple steps such as improving ventilation, using fans or air conditioning where possible, drawing curtains during the day, and aiming to keep bedrooms around or below 24 degrees Celsius at night may support better heart recovery during sleep. 

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This content is for informational purposes only and is not a substitute for professional medical advice.