A study has found that simply lowering the bedroom temperature appropriately at night can reduce the heart burden and stress response in the elderly. It is analyzed that the bedroom temperature can be an important variable in creating an environment where the heart can recover sufficiently during sleep.
The stress response is a physiological reaction that occurs when the sympathetic nervous system is activated in threatening situations, leading to increased heart rate and blood pressure, and the body being in a tense state. In contrast, during sleep, the parasympathetic nervous system becomes dominant, slowing the heart rate and switching the body to recovery mode. The researchers analyzed that a hot bedroom environment could disrupt this autonomic nervous system balance and excessively stimulate the sympathetic nervous system.
Researchers from Griffith University in Australia analyzed the effects of nighttime bedroom temperature on heart rate and stress response in individuals aged 65 and older. As a result, when the bedroom temperature was maintained at 24°C during sleep, the stress response on the heart was relatively low.
Conversely, when the nighttime bedroom temperature exceeded 24°C, there was a higher likelihood of increased heart rate and disruption of autonomic nervous system balance, showing a tendency towards dominance of the sympathetic nervous system and increased physiological stress.
Dr. Fergus O'Connor, who led the study, explained, "It is a normal physiological response for the heart rate to increase when the body is exposed to heat, as blood flow is sent to the skin surface to lower body temperature, causing the heart to work harder and longer than usual."
The problem arises if this state persists throughout the night. He pointed out, "If the heart is in an overloaded state for a long time, stress accumulates, and the ability to recover from heat exposure during the day is limited. Sleep is the time for the heart and autonomic nervous system to recover, but a hot environment disrupts this process."
This study is significant as it was conducted in real-life environments rather than in a laboratory. The study used recorded data from activity and heart rate monitoring devices worn on participants' wrists and temperature information obtained from sensors installed in the bedroom. The researchers comprehensively analyzed changes in nighttime bedroom temperature, heart rate, heart rate variability (HRV), and stress response indicators during the summer period.
The researchers stated that they have confirmed for the first time with actual data that as bedroom temperature increases, the heart stress response during sleep also increases. They also explained that if the bedroom temperature is significantly lower than 24°C, it can negatively affect health by disrupting sleep.
The researchers emphasized that these results are directly related to climate change. Dr. O'Connor stressed, "The frequency of hot nights is increasing due to climate change, which can independently increase the risk of cardiovascular disease and mortality by hindering sleep and autonomic nervous system recovery."
It was also pointed out that while there are guidelines for the maximum recommended indoor temperature (26°C) during the day in several countries, there are no clear recommendations for nighttime sleep environments. He added, "It is necessary to establish indoor temperature guidelines for nighttime to protect vulnerable groups, including the elderly."
This research result was published in the international medical journal 《BMC Medicine》 under the title 'Effect of nighttime bedroom temperature on heart rate variability in older adults: an observational study.'
[Frequently Asked Questions]
Q1. Why does bedroom temperature affect the heart and autonomic nervous system?
When body temperature rises, the body increases heart rate and activates the sympathetic nervous system to release heat. If this state persists throughout the night, the action of the parasympathetic nervous system, which is responsible for recovery during sleep, is suppressed, which can increase the burden on the heart.
Q2. Can the same results apply to younger people?
This study was an observational study targeting individuals aged 65 and older, so it cannot be definitively stated that it applies equally to younger age groups. However, it can be interpreted as evidence showing the importance of nighttime indoor temperature management for protecting vulnerable groups, as the elderly are more susceptible to heat.
Q3. Is it harmful to health if it is too cool at night?
The researchers did not recommend excessively lowering the bedroom temperature. The standard presented in this study was around 24°C, which is a level of 'moderate cooling' that does not increase heart stress response in the elderly. Excessively low temperatures can cause chills, sleep disturbances, and muscle tension, so adjustments should be made considering individual comfort and health status.
