June 17, 2025, 5:07 pm | Read time: 6 minutes
In Germany, the hot season has begun, and many people are noticing a decline in sleep quality. A new study reveals, among other things, how significantly high nighttime temperatures affect those already suffering from sleep-related conditions, such as sleep apnea. FITBOOK writer Laura Pomer delves into the study’s findings and has spoken with the study’s lead author about it.
The so-called obstructive sleep apnea syndrome (OSAS) leads to repeated breathing interruptions during sleep due to a temporary narrowing or blockage of the upper airways. It is considered a serious medical condition. It is believed that if left untreated, it can significantly reduce life expectancy.1 The nighttime lack of oxygen can strain the heart, potentially leading to various severe secondary diseases. More information on this here. Various circumstances and external factors can worsen the symptoms. These range from being overweight to an unfavorable sleep position to the consumption of alcohol. High temperatures are also apparently significant for sleep apnea patients. This is shown by a new study from Australia’s Flinders University. 2
Overview
How High Temperatures Affect Sleep Apnea
The researchers have examined the topic of “high temperatures” over the long term against the backdrop of climate change. Based on their findings, they assume that sleep apnea will increasingly become a greater health and economic burden worldwide. As the authors explain in a press release, the number of affected individuals could double in many countries over the next 75 years.3 Additionally, high nighttime temperatures on hot days immediately increase the likelihood of breathing interruptions during sleep, as the study confirmed.
Study Procedure
The researchers analyzed sleep data from more than 116,000 people from various countries. About 25.4 percent of the predominantly male participants suffered from a moderate form of obstructive sleep apnea, while 8.9 percent had a severe form. The remaining participants showed no corresponding abnormalities. All participants had used a special medical measuring device under their mattress for an average of about 3.5 years. This device continuously recorded various specific values during sleep beyond just the sleep duration. Central to these values was the so-called Apnea-Hypopnea Index (AHI). This index indicates how many breathing interruptions or shallow breaths occur per hour of sleep and is thus a crucial criterion for assessing the severity of sleep apnea. Another aspect was the timing of the breathing interruptions within a night.
For each individual, sensor recordings from 500 different nights were available, resulting in data from around 62 million nights in total. The researchers compared these data with local weather records, which provided the outside temperatures of the preceding 24 hours.
Higher Temperatures = More Breathing Interruptions Due to Sleep Apnea
The analysis revealed that particularly hot days significantly increase the risk of nighttime breathing interruptions. Specifically, the likelihood of corresponding sleep apnea symptoms increased by about 45 percent when the temperature was around 27 degrees Celsius, compared to cool days at about 6 degrees Celsius. Severe cases of sleep apnea occurred up to 50 percent more frequently on days with high temperatures. According to the researchers, it is also known that sleep apnea patients wear their sleep masks, which treat the condition with CPAP (continuous positive airway pressure) therapy, less often or for shorter periods in the heat.
Whether this was the cause in the specific case, there is no information available. “We did not have access to treatment data,” admits lead study author Dr. Bastien Lechat when asked by FITBOOK. Whether treatment adherence could have played a role in the results remains initially unclear.
Hot Weather Disrupts Sleep Architecture
“Our main hypothesis is that hot weather disrupts sleep architecture, leading to lighter sleep during the night,” says Dr. Lechat to FITBOOK. Since sleep apnea is known to be more severe in lighter sleep phases, this could help explain the observed effects. The researcher points to a 2009 study whose results suggest that the severity of sleep apnea is significantly reduced in deep sleep.4
The observed effect—a worsening of symptoms—was particularly pronounced in European countries. According to the researchers, this could be related to structural conditions. For example, air conditioning is much less common in Europe than in the U.S. or Australia. Dr. Lechat: “We believe this could partially explain the differences observed between countries.”
Long-term Possible Consequences for Society
As mentioned above, the researchers also aimed to estimate how the diagnosis of obstructive sleep apnea (OSA) poses an increasing threat to general health and the economy. To this end, they considered various climate scenarios and used a special calculation model for health economic evaluation. They based their analysis on the so-called “disability-adjusted life years” (DALYs). This is a metric used by the World Health Organization that accounts for disease and injury consequences as well as premature deaths.
According to Dr. Lechat, the calculation found that in 2023 alone, the climate change-induced increase in OSA prevalence in the studied countries led to a loss of about 800,000 healthy life years. This figure is comparable to what is caused by Parkinson’s, bipolar disorders, or chronic kidney diseases. For the future, the authors expect a significant increase. With global warming of about 1.8 degrees Celsius by 2100, the heat-induced burden of obstructive sleep apnea could increase by 1.2 to 3 times, depending on the scenario and region.
Study Limitations
As with most large data analyses, there are certain limitations. The temperature data came from weather reports. How warm it actually was in the participants’ bedrooms was not recorded. Additionally, the majority of the participants were male and from industrialized countries, which limits the transferability of the results to other groups. The causes of the link between heat and sleep apnea were not further investigated, but only statistically demonstrated.
Several questions remain open. The most significant: Do the temperatures really cause the increased symptoms, or are the observations solely due to the behavior of sleep apnea patients? It is conceivable that warmth directly affects breathing control or muscle tone during sleep. “This mechanism could play a role,” confirms Dr. Lechat. There is a need for further prospective studies to investigate the mechanisms.
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Recommendations for Sleep Apnea Patients
Even now, sleep apnea patients can draw relevant information from the observations. They should try to create as cool a room climate as possible during the summer. It is advisable to limit the ventilation of the bedroom to the early morning hours and to keep windows and curtains or blinds closed during the day. It is important not to remove your CPAP mask at night just because you are warm. Also, ask your partner to pay attention and wake you if necessary so that you can put the device back on properly.