The sleep-wake cycle, or the circadian rhythm, is the governing driver of many bodily functions and behaviors in many organisms, humans included. In a lecture by Dan Cavanaugh on his paper “The cell-intrinsic circadian clock is dispensable for lateral posterior clock neuron regulation of Drosophila rest-activity rhythms” (Cavanaugh et al., 2025), he discussed the many roles the circadian rhythm plays in humans, including hormone regulation, body temperature control, metabolic changes, and immune responses, demonstrating its major role in everyday life.
In the lecture, Cavanaugh noted that temperature changes throughout the day in rhythmic ways, with body temperature being lowest in the early morning (around 5AM) and highest around dusk (around 6PM). As mentioned above, body temperature is largely controlled by the circadian rhythm, which is governed by a network of clock neurons throughout the brain, with about 240 of these neurons in Drosophila. These neurons are subdivided into regions based on their activity/function, with lateral posterior clock neurons, or LPNs, being the focus of Cavanaugh et al.’s study. One finding was that LPNs are particularly sensitive to temperature input, sometimes even syncing to “temperature oscillations in the presence of conflicting light and temperature entrainment signals” (Cavanaugh et al., 2025). Cavanaugh et al. also note that LPNs receive direct input from temperature-sensitive neurons, which is the main enhancer of this phenomenon. The findings showed that with increases in temperature, there is increased activity in LPNs, which leads to promoted sleep during the daytime “siesta” and decreased nighttime sleep (Cavanaugh et al. 2025).
Similarly, human sleep duration and quality are greatly impacted by changes in temperature, specifically by increases in temperature, as discussed in Hajdu’s 2024 article, “Temperature exposure and sleep duration: Evidence from time use surveys.” In his study, he investigated the impact of rising temperature on the duration of sleep using data from “nationally representative Hungarian time use surveys between 1976 and 2010” (Hajdu, 2024). The findings from his and past studies are generally that increases in daily ambient temperature lead to decreases in the amount of sleep individuals get, by about 13.1 minutes (or even more if preceding days were also hotter) (Hajdu, 2024). This finding is similar to Cavanaugh et al.’s, as increased temperature leads to decreased nighttime sleep. Although Cavanaugh et al.’s findings also show increases in daytime sleep, these studies reflect a common theme: temperature plays an important role in sleep time/quality.
These types of sleep studies are incredibly important, as sleep and circadian rhythm are major regulators of quality of life. Also, with global temperatures rising due to global warming, the impact of temperature on sleep is also becoming increasingly relevant. Hajdu’s study discusses four possible projections of temperature increases for the end of the 21st century—SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP4-8.5, with the numbers following the dash being the estimated temperature increase. Hajdu discusses the overall impact of global warming on sleep loss through these four projections in the 2090s, with a predicted annual loss of sleep of 6.8 hours for SSP1-2.6 and 14.8 hours for SSP4-8.5, which are non-negligible results (Hajdu 2024). This lack of sleep is also projected to be concentrated in the warmer months—summer and early fall—as that is when temperature is highest.
As mentioned in Hajdu’s study, short-term and continued sleep loss can have a profound impact on one’s life—increased risk of diabetes, weight gain, and heart disease, just to name a few (Hajdu, 2024). “Climate change-induced sleep loss is [also] likely to have sizable macroeconomic consequences” (Hajdu, 2024), which is just one more compelling piece of evidence that temperature plays an important role in sleep. With the information from Cavanaugh et al. and Hajdu’s studies, even small changes, such as slight increases in temperature, can change the quality and amount of sleep that one gets. Going forward with sleep research, studies focusing on combating increased temperature-induced sleep loss will be of increasing importance, which should help to prevent the negative consequences of temperature increases on sleep.
References
Cavanaugh, D. J., Guerrero, C. Y. P., Cusick, M. R., Samaras, A. J., & Shamon, N. S. (2025). The cell-intrinsic circadian clock is dispensable for lateral posterior clock neuron regulation of Drosophila rest-activity rhythms. Neurobiology of Sleep and Circadian Rhythms, 18, 100124. https://doi.org/10.1016/j.nbscr.2025.100124 (pmc.ncbi.nlm.nih.gov)
Hajdu, T. (2024). Temperature exposure and sleep duration: Evidence from time use surveys. Economics & Human Biology, 54, 101401. https://doi.org/10.1016/j.ehb.2024.101401 (sciencedirect.com)
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