Efficacy of 1 and 5 mg Doses of Melatonin on Heat Tolerance While Wearing NBC Protective Clothing


  1. McLellan, T.M.
Corporate Authors
Defence and Civil Inst of Environmental Medicine, Downsview ONT (CAN)
This report summarises the findings from 2 studies which examined whether the reported hypothermic effect of melatonin ingestion increased tolerance to the heat stress of wearing NBC protective clothing. In the first study, trials were conducted either in the morning or afternoon, 2 each in the morning (0930 h) and afternoon (1330 h) following the double-blind ingestion of either two placebo or two 1 mg capsules of melatonin. The heat stress test consisted of intermittent walking and seated rest at 40C and 30% relative humidity while waring NBC protective clothing. In the second study, subjects performed 4 trials which involved 2h of rest in combat clothing at either 23C or 40C followed by exercise at 40C while wearing the NBC ensemble. A single 5 mg dose of melatonin was ingested following 30-min of rest. In the first study, rectal temperature (Tre) was not affected by melatonin ingestion but Tre was increased during the afternoon trials by 0.3C compared with the morning exposures and these differences remained throughout the heat stress such that final Tre was also increased for the anternoon (39.2C) versus the morning (39.0C) trails. Since the rate of heat storage was similar, tolerance times (108, 111, 110, and 107 min for the morning melatonin and placebo trials, and the afternoon melatonin and placebo trials, respectively) were not different among the trials. TRUNCATED
Circadian rhythm
Report Number
DCIEM-TR-1999-108 — Technical Report
Date of publication
01 Oct 1999
Number of Pages
Hardcopy;Document Image stored on Optical Disk

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