Differential Psychological Effects of Daytime and Nighttime Heat Exposures on Anxiety: A Randomized Crossover Trial

This study employed a randomized controlled crossover trial design. Between July and August 2025, 41 college students participated in 8 h exposures to daytime heat (32 °C), nighttime heat (30 °C), and a control temperature (26 °C).

Anxiety, biomarkers related to inflammation, oxidative stress, neuroendocrine responses, and neuroplasticity were assessed before and after each exposure. Daytime heat exposure was associated with a 24.71% (13.32%–36.11%) increase in anxiety scores and was accompanied by elevated levels of the oxidative stress biomarkers malondialdehyde (MDA) and oxidized low-density lipoprotein (Ox-LDL). Nighttime heat exposure was also associated with an increase in anxiety scores of 27.80% (17.32%–38.29%) and was linked to broader biological alterations, including increased levels of interleukin-1β (IL-1β) and MDA, as well as higher cortisol and lower brain-derived neurotrophic factor (BDNF) levels.