Melatonin has no effect on tolerance to uncompensable heat stress in man


  1. McLellan, T.M.
  2. Smith, I.F.
  3. Gannon, G.A.
  4. Zamecnik, J.
Corporate Authors
Defence and Civil Inst of Environmental Medicine, Downsview ONT (CAN)
This study examined whether a 5 mg dose of melatonin induced a lwer rectal temperature (Tre) response at rest in both a cool and hot environment while wearing normal military combat clothing, and then examined the influence of this response on tolerance to exercise in the heat while wearing protective clothing. Nine men performed four randomly ordered trials involving 2 h of rest at ambient temperatures of either 23C or 40C followed by exercise at an ambient temperature of 40C. The double-blind ingestion of placebo or melatonin occurred after 30 min of rest. The mean Tre during rest at 23C had decreased significantly from 36.8 (SD 0.1) C to 36.7 (SD 0.2) C at 90 min following the ingestion of the drug, whereas values during the placebo trial did not change. The lower Tre response during the melatonin trial remained during the first 50 min of exercise in the heat while wearing the protective clothing. Since the final mean Tre at the end of exercise also was significantly reduced for the melatonin (39.0 (SD 0.4) C) compared with the placebo (mean 39.1 (SD 0.3) C) trial, tolerance times approximated 95 min in both conditions. During rest at 40C, melatonin did not affect the mean Tre response which increased significantly during the last 90 min from 36.9 (SD 0.1) C to 37.3 (SD 0.1) C. TRUNCATED
Rectal temperature;heat flow
Report Number
DCIEM-SL-1999-095 — Scientific Literature
Date of publication
30 Aug 2000
Number of Pages
Reprinted from
Eur J Appl Physiol, vol 83, 2000, p 336-343)
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