The hypothermic effect of melatonin on core body temperature: is more better?
Level 2 - randomized trial
Individual randomized double-blind crossover trial.
PubMed 8836952 · doi:10.1111/j.1600-079x.1996.tb00258.x
What was done
Researchers evaluated the dose-response effect of daytime melatonin on core body temperature (CT) in 32 healthy adults (aged 18–38). Participants were divided into four groups of eight. Each participant completed two 12-hour bedrest protocols (0800 to 2000 hr) in a double-blind, counterbalanced crossover design, receiving either a sucrose placebo or an oral melatonin dose (0.1, 0.5, 1.0, or 5.0 mg) at 1600 hr while CT and plasma melatonin concentrations were monitored.
What was found
Melatonin peaked in plasma after 1 hour across all doses, with mean elimination half-lives between 33 and 47 minutes. At lower doses (0.1 and 0.5 mg), mean CT dropped by 0.05–0.15 °C over 2–3 hours, with high inter-individual plasma variability. At higher doses (1.0 and 5.0 mg), CT dropped by 0.25–0.30 °C within 30–60 minutes; at 5.0 mg, CT remained suppressed for the rest of the study period.
Why it matters
If melatonin's hypnotic effects depend on lowering core body temperature, daytime or evening doses of at least 1.0 to 5.0 mg appear necessary to reliably induce hypothermia across individuals.
Limits
The total sample size was small (n = 32), with only 8 participants per dose condition. The study evaluated daytime administration (1600 hr) during sustained bedrest in young healthy adults, which may not fully reflect nighttime sleep physiology or clinical insomnia populations.
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