Background:The benefits of meditation are well documented, but the biochemical mechanisms have not been fully identified. One effect mechanism may be via influence on neurotransmitters.Material/Methods: Therefore, plasma melatonin and blood serotonin concentrations were measured before and after one hour of meditation in advanced male meditators (n=27, mean age 46 years). They were compared with a matched reference group (n=29, mean age 43 years) who rested for one hour. In the meditators, melatonin and serotonin from before and after three consecutive hours of meditation were also compared.Results: Initially, the median melatonin level was 4.9 pg/ml–1 in the meditators and 3.1 pg/ml–1 in the reference group (p<0.01). After one hour of practice, melatonin had decreased to a median of 3.4 pg/ml–1 in the meditators (p<0.0001), but was unchanged in the reference group. After three hours of meditation, melatonin had declined further in the meditators. After one hour of practice, serotonin concentrations decreased in both the meditators and the reference group (p<0.01).
Conclusions: The findings suggest that advanced meditators have higher melatonin levels than non-meditators. Melatonin decreases during long meditation, a finding the study does not explain. Serotonin declines after both one-hour meditation and rest, indicating that serotonin may be a marker of general rest and not meditation-specific relaxation.

Keywords: Meditation, Melatonin - blood, Neurotransmitter Agents - metabolism, Relaxation, Relaxation Techniques, Rest, Serotonin - blood, Time Factors, Meditation, Melatonin - blood, Neurotransmitter Agents - metabolism, Relaxation, Relaxation Therapy, Rest, Serotonin - blood, Time Factors