Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder, affecting nearly one billion adults worldwide. The severity of OSA is usually quantified using the apnea-hypopnea index (AHI), which measures the number of partial or complete upper airway collapses per hour of sleep. Untreated OSA is associated with a wide range of adverse health outcomes, travel incidents, and increased all-cause mortality. Although high ambient temperatures are associated with reduced sleep duration and quality, the impact on OSA severity has been unknown. A recent global study, incorporating a large amount of data, has shed light on the alarming relationship between rising temperatures and the burden of OSA.

Extensive study and methodology This large study analyzed data from 116,620 users of an FDA-approved OSA monitor placed under the mattress over a 3.5-year period, representing a total of approximately 62 million nights of sleep. Data on daytime ambient temperature were obtained from the ERA5 database. The study examined the relationship between daytime temperature and nighttime OSA status, with participants having an average AHI of 11.3 events per hour. The researchers used time-series methods commonly used in environmental health studies and accounted for potential confounding factors such as cloud cover, humidity, air pollution, and total sleep time.

Key findings: Direct impact of heat on OSA The study revealed a nonlinear relationship between 24-hour daily average ambient temperature and the risk of OSA the following night. Globally, higher temperatures (99th percentile; 27.3°C) were associated with 45% higher chance of developing OSA on a given night compared to days with lower temperatures (25th percentile; 6.4°C). The odds of severe OSA were up to 49 % higher on days with high temperatures. This effect varied by country, and was generally stronger in European countries, where the odds of nocturnal OSA could increase by up to twofold. Interestingly, the association between temperature and nocturnal OSA was stronger in men, in users with a higher body mass index (BMI), and in participants with a habitual sleep duration of more than 6 hours. However, age did not have a strong influence on this association.

Huge strain on health and productivity The researchers quantified the health and economic burden of OSA related to warming using measures such as years of healthy life lost (DALYs) and workplace productivity. In 2023, the increase in OSA prevalence due to global warming was associated with a loss of 788,198 healthy years of life (DALYs) in the 29 countries studied, which included 27,180 years of life lost due to premature death. The economic cost of this health impact in 2023 is estimated at approximately 68 billion USDThese estimates were approximately twice as high as in 2000.

In terms of workplace productivity, the increase in OSA prevalence due to higher temperatures in 2023 led to further 80 million days of face-to-face work (present at work but with reduced capacity) and 25 million days of absence in the 29 countries studied. The total economic cost of this work loss was estimated at $30 billion.

Future scenarios and urgency of action Projections indicate that in scenarios with a temperature increase of ≥1.8°C above pre-industrial levels, OSA burden could double by 2100Such scenarios could result in additional losses of between 12 and 36 million DALYs (disability-adjusted life years) and 0.5 to 1.3 million years of life lost by 2100, with health costs of between US$1.0 and US$2.8 trillion. Labor productivity losses would also increase significantly, with additional costs of between US$0.9 and US$2.0 trillion between 2023 and 2100.

Study acknowledges some limitations, including potential underestimation of lower socioeconomic groups in the study sample, which had access to sleep monitoring devices and likely heat stress mitigation strategies such as air conditioning. Accurate data on indoor temperatures and clinical information on participants' comorbidities were also unavailable.

In conclusion, this study underlines the potential significant impact of rising ambient temperatures on the prevalence of OSA worldwideWithout a significant policy change to slow global warming, the health and economic burdens associated with OSA could double by 2100. These results highlight the urgent need to limit global warming to 1.5°C above pre-industrial levels, in line with the Paris Agreement, and implement targeted measures to minimize the impact of the increasing prevalence of OSA. Investments in limiting global warming would prove to be a cost-effective strategy for preventing climate-related sleep disorders and their consequences. Spring

The study was published in the journal nature.com

Glossary of key terms

• Apnea-hypopnea index (AHI): A measure of the severity of obstructive sleep apnea (OSA), which quantifies the number of complete breathing stops (apneas) and partial reductions in airflow (hypopneas) per hour of sleep.
• Obstructive sleep apnea (OSA): The most common sleep-related breathing disorder, characterized by repeated episodes of partial or complete collapse of the upper airway during sleep, resulting in interrupted breathing.
• Ambient temperature: The temperature of the external environment that surrounds people and affects their thermal comfort and physiological responses.
• Welfare burden: The overall impact of a health condition (such as a disease or disability) on the quality of life and health of a population. It is quantified using measures such as disability-adjusted life years (DALYs).
• Workplace productivity: The degree to which employees are effective and efficient in completing work-related tasks. Reduced productivity can be caused by absenteeism (complete absence) or presenteeism (presence at work but with reduced performance).
• Disability-adjusted life years (DALYs): A standardized global measure of the burden of disease, expressed as the number of years of healthy life lost due to disease, injury or premature mortality. It is the sum of YLL and YLD.
• Years of Life Lost (YLL): The number of years of life lost due to premature mortality compared to life expectancy.
• Years lived with disability (YLD): Number of years lived in less than optimal health or with disability.
• Pre-industrial levels: Reference temperature levels from a period before significant anthropogenic greenhouse gas emissions, usually defined as the period around 1850–1900.
• Shared Socioeconomic Pathways (SSP): Scenarios developed for the IPCC (Intergovernmental Panel on Climate Change) assessment report that describe alternative socio-economic development trajectories and their impact on greenhouse gas emissions and climate change (e.g. SSP126, SSP245, SSP370, SSP585).
• ERA5: The fifth generation of the European Reanalysis, a comprehensive dataset of global atmospheric, land and ocean variables from the past, providing accurate weather data.
• Nearable (wearable technology): A term used to describe technologies that are “nearly wearable” or located in close proximity to the user, such as a sleep sensor under the mattress.
• Presenteeism: A condition where an employee is present at work but is not working at full capacity due to health problems.
• Absence: The complete absence of an employee from work, usually due to illness or other health problems.