Effects of morning melatonin administration on electroencephalographic theta to alpha power ratio in reproductive versus postmenopausal healthy female volunteers

Objective: The aim of the present study was to investigate the effect of exogenous morning melatonin administration on the electroencephalogram of reproductive versus postmenopausal women. Methods: Twenty-six female, reproductive and postmenopausal healthy volunteers were randomly assigned to receive melatonin or placebo at 9:00 in the morning. Twelve electroencephalographic recording sessions were performed before the intake of melatonin or placebo and at 15, 30, 45, 60, 75, 90, 120, 150, 180, 240, and 300 min. Theta to alpha ratios for every subject, channel and session were mathematically processed to yield the logarithm (base 10) of the spectral (theta power)/(alpha power) ratio for the 12 electroencephalographic sessions, weighted to the baseline ratio (LwRs). The LwRs were compared between melatonin groups (reproductive versus postmenopausal women) and also between melatonin and control groups. Results: Data from 24 women were analyzed. The LwRs in the reproductive women were significantly lower than the LwRs in postmenopausal women at 60, 180, 240 and 300 min after melatonin consumption (p = 0.007, 0.041, 0.008 and 0.040 respectively). In reproductive women, the LwRs of subjects who received melatonin were significantly lower compared to their controls at 60, 240 and 300 min after melatonin or placebo intake (p = 0.005, 0.006 and 0.019 respectively). In postmenopausal women, no significant differences in the LwRs were calculated for any time point between melatonin and control groups. Conclusions: Our results show that morning melatonin administration produces no electroencephalographic changes in postmenopausal women. In contrast, electroencephalographic changes suggesting a possible awaking effect were observed in reproductive women.

► The logarithm of the spectral theta/alpha power ratio was significantly reduced in reproductive women who received melatonin. ► Melatonin was associated with an awaking effect in the EEG of reproductive women. ► Melatonin produced no EEG changes in postmenopausal women.