Serum melatonin and serotonin levels in long-term skilled meditators

Meditation and mindfulness practices have existed in diverse Asian cultures throughout history with multiple techniques, forms and definitions. Mindfulness is an intrinsic ability of the human mind which has been defined as “the awareness that develops by purposefully paying attention to the present and to the unfolding experiences moment by moment”12. These meditation and mindfulness practices integrate brain functions with various physiological mechanisms to preserve the mental and physical wellbeing23

Transcendental meditation, Buddhist and Dhammakaya meditation, Mindfulness Based Stress Reduction (MBSR), Progressive Muscle Relaxation, and multiple types of yoga are some of the practices that follow the core concept of being aware of the self and surroundings, focusing on the present moment by blocking all distraction while purposefully controlling the breath and physical movements7. Meditation is a common practice among the Theravada Buddhist community in Sri Lanka. Samatha (Tranquility) and Vipassana (Insight) are the two main stages of Theravada Buddhism which are practiced respectively to attain calmness of the mind and nibbana, a state of complete inner peace.

The initial research interest of meditation was focused on stress, pain, coping, and quality of life but recently, it has gained attention as a complementary treatment for various clinical modalities. Research implies some of the benefits of meditation on the nervous system are positive changes in autonomic activity, cognition, sensory perception, hormones, and neurotransmitters26. Growing evidence demonstrates that mindfulness and meditation practices modulate various psycho-physiological processes13.

Recent research has found that mindfulness and meditation practices are involved in maintaining a proper sleep-wake cycle facilitating to enhance the quality of sleep. Sleep quality is an important determining factor of health and wellbeing16. The neurotransmitter, melatonin, sometimes referred to as the ‘sleep hormone’ or ‘hormone of darkness’ which is produced by the pineal gland in the brain regulates the sleep-wake cycle36. Melatonin is synthesized endogenously from the amino acid tryptophan (derived from serotonin) by the enzyme 5-hydroxyindole-Omethyltransferase. Melatonin biosynthesis is influenced by the day-night cycle and is involved in the regulation of circadian rhythm14,38. Melatonin reaches its peak levels between midnight and 4 am. Melatonin has found to reduce pain sensitivity and also acts as an antioxidant and immunomodulator, stimulating the immune system and the antioxidative defense system, thus delaying aging4,20. Some studies have shown that melatonin can even inhibit the growth of certain types of cancer6,20 and prevent coronary atherosclerosis, while upregulating the immune system2,30,31. Melatonin secretion is altered in patients suffering from affective disorders, eating disorders, and schizophrenia, indicating that low melatonin levels cause depressive phases27.

Previous studies have shown that different mindfulness and meditation types have effects on melatonin levels of different biological fluids in the body. Massion et al.,20 tested the hypothesis that the regular practice of mindfulness meditation is associated with increased physiological levels of melatonin and have obtained some positive results. Transcendental meditation (TM)- Sidhi or yoga showed significantly higher plasma melatonin levels in the period immediately following meditation compared with the same period at the same time on a control night35. Harinath et al.,10 evaluated the effect of Omkar meditation and Hatha yoga on melatonin secretion and found melatonin levels at 2:00 AM, 3:00 AM and 4:00 AM after 3 months of yoga and meditation were significantly higher compared to that of control. They also found that the rise of melatonin level in the yoga group showed a significant correlation with well-being score. Solberg et al.,32 measured plasma melatonin secretion levels during ACEM meditation (ACEM is a meditation organization that originated in Oslo, Norway), and found that advanced meditators have higher melatonin levels than non-meditators, although melatonin levels decrease during long-term meditation. Chinese Original Quiet Sitting (COQS) elevated the nighttime salivary melatonin levels by showing statistically higher melatonin level in the COQS meditation group and the level was unchanged in the control group after nighttime meditation17. Another study showed that, diurnal serum melatonin levels were significantly higher in Vipassana meditators compared to non-meditating controls24 and the morning melatonin level showed a positive correlation with the N3 sleep stage.

Serotonin, the precursor of melatonin and a powerful neurotransmitter in the central nervous system acts on the digestive tract and regulates the physiological mechanisms such as body temperature, motor control, and circadian rhythm8. Serotonin affects mood by producing a general sense of satisfaction and relaxation7 which helps to maintain the emotional wellbeing and overall health. Serotonin also plays a role in regulating sleep-wake cycles and circadian rhythms29. It is an important neurotransmitter in the descending analgesic pathway from the brain stem to the dorsal horn of the spinal cord, which is important in pain relief33.

Several studies have shown associations between low levels of serotonin and serotonin receptors with depression and related conditions. Low levels of serotonin in plasma and serum are correlated with feelings of depression, anxiety and higher sensitivity to noxious stimuli18. Lower levels of serotonin in the cerebrospinal fluids have been shown to correlate with depression1. Patients diagnosed with panic disorder had about one-third lower level of serotonin 1A receptors compared to healthy individuals indicating that depression is associated with deficiency of serotonin activity on receptors15. Studies with 5-HT1A (5-Hydroxytryptamine receptor 1A) serotonin receptor knockout mice have indicated that they have increased avoidance, decreased locomotor activity, and increased autonomic arousal which suggests increased anxiety-like behavior9,28. However, a recent review article by Moncrieff et al.,22 on the association of depression with serotonin levels revealed that there was no consistent evidence supporting the hypothesis that depression is caused by lowered serotonin activity or concentrations. Although, the same review article identified multiple evidence showing that antidepressants were strongly associated with lower serotonin levels22.

Several studies have shown that after meditation, the breakdown products of serotonin (5-HT) in urine are significantly increased, suggesting an overall elevation in serotonin during meditation26. Studies have found that following the transcendental meditation, the main breakdown product of serotonin, 5-hydroxyindole-3-acetic acid (5-HIAA) in urine was significantly increased5,37. In contrast,32 found that blood serotonin concentrations decreased in meditation and reference groups after one hour of meditation.

Serotonin has been closely linked to melatonin; both play an important role in mood stabilization (including depression), positive affect, stress-prevention and aging27. The physiological effects of meditation suggest the possibility of a role played by either melatonin or serotonin or by both in influencing mood changes and relaxation21.

Even though, there are early studies showing the effect of different mindfulness practices and meditation types on melatonin and serotonin levels, there is limited knowledge on the effects of Vipassana meditation technique on serum serotonin and melatonin levels collectively, especially in Sri Lanka. Therefore, this study was aimed to determine the serum levels (concentrations) of two different neurochemicals, serotonin and melatonin among long-term Vipassana meditators in Sri Lanka in comparison with age, gender and education level matched non-meditator controls.

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