Efficacy of 1 and 5 mg Doses of Melatonin on Heat Tolerance While Wearing NBC Protective Clothing.
Abstract
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 40 deg C and 30% relative humidity while wearing NBC protective clothing. In the second study, subjects performed 4 trials which involved 2h of rest in combat clothing at either 23 deg C or 40 deg C followed by exercise at 40 deg C 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 (T(re)) was not affected by melatonin ingestion but T(re) was increased during the afternoon trials by 0.3 deg C compared with the morning exposures and these differences remained throughout the heat stress such that final T(re) was also increased for the afternoon (39.2 deg C) versus the morning (39.0 deg C) trials. 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. During the second study, T(re) during rest at 23 deg C decreased significantly from 36.8 deg C to 36.7 deg C following the ingestion of the drug, whereas values during the placebo trial did not change. The lower T(re) response during the melatonin trial at rest remained during the exercise in the heat while wearing the NBC protective clothing. However, since the T(re) tolerated at exhaustion also was significantly lower for the melatonin (39.0 deg C) compared with the placebo (39.1 deg C) trial, tolerance times approximated 95 min in both conditions.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1999
- Accession Number
- ADA372446
Entities
People
- T. M. Mclellan
Organizations
- Defence Research and Development Canada