The summer of 2026 in Europe and the US is set to record high temperatures and heat-related deaths. Older adults and those with chronic health problems are most affected, but everyone is affected to some extent. Considerable research has been done to determine how high temperatures and humidity affect the quality of our sleep. This is a good time to summarize what we know.
First, let’s see what happens to our body temperature during a normal night’s sleep. Our core temperature, which is regulated by the circadian cycle, drops slightly when we fall asleep and continues to drop, reaching its lowest point six hours later. Many of us can go to bed covered with just a sheet and wake up later to grab a blanket. The reduction occurs due to a slower metabolic rate and less heat production. After the low point, the body temperature rises as part of the circadian process, which leads to awakening. Controlling the temperature of the bedroom environment is important to support good sleep. Because air conditioning is less readily available in homes and apartments in northern European countries than in the US, cooling to a comfortable temperature is more difficult there.
How humidity and airflow affect sleep quality
High humidity mixed with heat is especially uncomfortable and we are all familiar with the heat index or what is sometimes called the “real feel”. A high quality HVAC system cools the entire home by pulling heat and moisture from the home. Good air flow and ventilation are also essential for optimal sleep. Window units are less efficient, and window or ceiling fans are even less so. Portable dehumidifiers are cost-effective and effective in homes that do not have good HVAC systems.
While the researchers controlled temperature and humidity and measured sleep (time to sleep, number and length of nighttime awakenings, REM and slow wave periods and overall duration), they concluded that a bedroom temperature of 62 to 82 degrees Fahrenheit and a relative humidity of 40% to 60% is conducive to good sleep. Of course, there are individual differences that can sometimes cause problems, as often two or more people share a bedroom, a bed and a bed.
Why is better cooling good for your health?
Children are more exposed to the negative effects of high temperatures and humidity than adults because of their higher body surface area to mass ratio. In a study conducted in our laboratory at Auburn University, we found that in families with less financial resources, good nighttime temperature control in the bedroom is often not available, and children sleep worse.
As we know that poor sleep can cause or exacerbate many health problems, high heat and humidity can affect health directly as well as indirectly through poor sleep. For those who can afford it, installing new or upgrading existing cooling and humidification systems is a good investment not only for comfort, but also for health.
