During the hot summer days, sleeping at night can be a major struggle. 2022 is found to have set the record for the highest overnight warmth. For this reason, the usual cooling off at night only occurred a handful of nights. Now, a new study has shown that hot nighttime temperatures are a fast way to disrupt night rest which could affect health negatively in many ways similar to a heatstroke.

Due to the crucial importance of a good night’s sleep rest, researchers from Japan set out to investigate the loss of life years that could occur as a result of heat-related sleep problems. At the same time, check how temperature increase can affect sleep.

Survey Methodology 

Japanese researchers surveyed a total of 1,284 participants living in Nagoya City, an urban heat island in Japan. Nagoya City was chosen since the city has witnessed an extreme rise in temperature due to climate change among the 3 major areas in Japan. Between the summers of 2011 and 2012, the researchers distributed self-administered questionnaires to be filled out among the participants to study their quality of sleep.

They took into account trouble sleeping and remaining asleep due to extreme heat, likewise, the rate of sleep medication use. In addition to that, they were able to link the overall quality of sleep with various day-to-day temperatures. 


The results showed that the frequency of daily sleep disturbances increases when the outside temperature rises above 24.8°C (76.64°F). In addition, the researchers found that the use of the Disability-Adjusted Life Years (DALY) measure to calculate the health years of over 2.2 million people was gotten to be 81.8 years. A value found to be quite similar in heatstroke. “That means that the damage to health caused by sleep disorders due to rising temperatures is comparable to that of heatstroke and must be addressed,” said Tomohiko Ihara, Associate Professor from the Graduate School of Frontier Sciences and lead author of the study.

Interestingly, they found that when it came to sleep challenges among the age groups, younger men faced more frequent sleep challenges than older men.

However, the authors pointed to some limitations in their study. First, the study did not put into consideration the use of air conditioning and whether usage may have lowered heat-related problems. In addition to that, the study authors neglected the state of mental health of the participants which might have influenced the outcome of the result. Lastly, it’s worth noting that children were absent from the study and the number of adults above the age of 70 was only 15 in 2011 and 26 in 2012. As a result, the study authors considered the population relatively low to be assessed.

Despite that, the authors recommend 25°C as the daily minimum standard when creating regulations for a nighttime temperature to prevent heat-related illnesses. They also hope climate change legislators realize the damages associated with hot nighttime temperatures and enact laws that counsel the public to favor better night sleep.

Finally, the team sees the need for more studies on a larger population; including older adults and children, to adequately contribute towards more proper policies.

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