2003 – Effects of humid heat exposure on sleep, thermoregulation, melatonin, and microclimate
Authors: K. Tsuzukia, K. Okamoto-Mizunoa, K. Mizunoc
Nine healthy young male volunteers were recruited to participate in a study involving three non-consecutive nights of polysomnographically and thermoregulatory measured sleep. Nightly urine samples were assayed for the melatonin metabolite 6-sulfatoxymelatonin (aMT6s). Experimental conditions were 26°C and 50% Relative Humidity/RD (26/50) and 32°C 80% Relative Humidity/RD (32/80), where the subjects wore pyjamas with cotton blanket. Rectal temperature (Tre) did not decrease during nocturnal sleep at 32/80. The duration of wakefulness and stage 1 sleep increased significantly at 32/80 compared to 26/50. Stage 2 and 4 sleeps were significantly shorter at 32/80 than at 26/50. Although there was no significant difference in urinary aMT6s between 32/80 and 26/50(n 1⁄4 6), the melatonin metabolite secretion tended to be lower at 32/80 than at 26/50 in accordance with the decrease in sleep efficiency index. Heart rate and sweat rate were significantly higher at 32/80 than at 26/50. The acute decrease in melatonin secretion during nocturnal sleep may be related to reduce sleep efficiency through thermoregulatory mechanisms.