Good news for hot sleepers. A cooler bedroom may do more than prevent sweaty nights. New research suggests overnight temperature could affect heart-related markers, particularly in older adults.
A study published in BMC Medicine looked at sleep temperature and heart health markers during a Queensland summer. Researchers followed 47 adults aged 65 and older who wore fitness trackers overnight. Bedroom sensors continuously monitored room temperature, which ranged from about 26°C to 32°C.
By the end of the study, higher bedroom temperatures were linked with:
- higher overnight heart rate
- lower heart rate variability (HRV), a marker linked with autonomic nervous system balance
- higher physiological stress, with effects increasing as temperatures rose
In simple terms, warmer rooms were associated with signs that the body was working harder overnight.
Why are the findings significant?
“Improved sleep quality is important for metabolic health, mental health, and ultimately cardiovascular health,” says board-certified cardiologist Dr Lily Dastmalchi. She adds that poor sleep quality can raise heart disease risk and is included as a factor in the cardiovascular health framework.
The link between temperature and autonomic nervous system disruption is also important. “The autonomic nervous system plays an important role in cardiovascular health by regulating vital systems, including heart rate, blood pressure, and heart muscle contraction strength,” says board-certified interventional cardiologist Dr Cheng-Han Chen. “Disruptions in this system can lead to serious heart conditions such as arrhythmia, heart failure, and even sudden death.”
This does not mean a warm night will cause heart disease. But it does suggest that regular exposure to high overnight temperatures may make it harder for the body to fully downshift during sleep, especially in older adults.
What does this mean for you?
The simplest takeaway is that a slightly cooler room may help the body settle overnight. “It is important to maintain a comfortable sleeping environment (in the 60s Fahrenheit) to optimize heart health,” Dr Chen says. That is roughly 16°C to 19°C. “Stress during sleeping, including that from high temperatures, can adversely affect sleep quality,” he adds.
There is also a point where “cool” becomes too cold for some people. Dr Dastmalchi says the relationship between temperature and sleep is not one-size-fits-all. “The association with sleep quality and temperature varies, where both too cold temperatures and too warm temperatures can decrease sleep quality,” she explains. “There are some adult populations that benefit from warmer temperatures, like people with poor circulation or conditions such as Raynaud’s.”
Temperature is only one part of the sleep equation. If sleep quality is consistently poor, other habits can play a role too, including screens in bed, caffeine or alcohol too late in the day and intense evening workouts.
The bottom line
Dr Chen says the study “is an important starting point for future research into how sleep temperatures can affect heart health,” but it has limits. “This was a small study involving 47 individuals; the results will need to be validated in a larger and more diverse population,” he says.
Dr Dastmalchi also notes that the research was observational, which means it cannot prove cause and effect. Participants slept in their own homes, so other factors may have influenced results. Still, lowering bedroom temperature slightly may be a simple, low-effort way to support better sleep and potentially reduce overnight stress on the body.
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