This question might have been asked before, but:
What is the current thinking on what effect supplementation with Melatonin, say 5mg a night, might have on overall serotonin levels. Is this something to take into account when supplementing with Melatonin for a healthy 30-40 y/o person.
Any other thoughts on the pros and cons of melatonin supplementation, and dosages would be welcomed.
Really interesting question. Since melatonin is synthesized from serotonin in the the brain, it would seem possible that exogenous melatonin would reduce the brain's turnover of serotonin. I managed to find a couple studies that examined this in rats:
Effects of neonatal melatonin administration on the extra-hypothalamic regions in rat brains: effects on the serotonergic system.
Muneoka K, Ogawa T, Takigawa M.
Department of Neuropsychiatry, Faculty of Medicine, Kagoshima University, Japan. KHB20641@nifty.ne.jp
The effects of 100microg melatonin injection at postnatal day 5 (PD 5) on the development of the central serotonergic systems in male and female rats were investigated. The contents of serotonin (5-HT) and 5-hydroxy-3-indolacetic acid (5-HIAA) were measured in several extrahypothalamic regions at 3, 10 and 42 weeks of age. The neonatal melatonin administration increased both 5-HT and 5-HIAA levels in the striatum throughout the examined period. In the hippocampus, an increase in 5-HIAA contents by neonatal melatonin administration was found at 3 weeks but not 10 or 42 weeks of age. There were no significant differences in the effects of melatonin between male and female rats. These results indicated that exogenous melatonin administration during the early neonatal period influenced the development of the serotonergic systems in extrahypothalamic regions including the hippocampus and the striatum.
Melatonin effects on serotonin synthesis and metabolism in the striatum, nucleus accumbens, and dorsal and median raphe nuclei of rats.
Míguez JM, Martín FJ, Aldegunde M.
Laboratorio de Fisioloxia Animal, Facultade de Bioloxia, Universidade de Santiago de Compostela, Spain. firstname.lastname@example.org
This work examined the influence of the pineal gland and its hormone melatonin on the metabolism of serotonin (5-HT) in discrete areas of the forebrain, such as the striatum and the nucleus accumbens, and the midbrain raphe. The content of 5-HT and its major oxidative metabolite, the 5-hydroxyindoleacetic acid (5-HIAA), as well as the in-vivo tryptophan hydroxylation rate were examined after long-term pinealectomy (one month) and daily melatonin treatment (500 micrograms/kg; twice daily for ten days) in pinealectomized rats. Pinealectomy did not alter 5-HT content in any of these brain areas, but it significantly increased the content of 5-HIAA in striatum and the 5-HIAA/5-HT ratio in nucleus accumbens. The normal values of these parameters were recuperated after administration of exogenous melatonin, but it also increased the rate of tryptophan hydroxylation in both areas. In addition, melatonin treatment decreased the levels of 5-HIAA in dorsal raphe nucleus. These data suggest that the pineal gland, through the secretion of melatonin, modulates the local metabolism of 5-HT in forebrain areas by acting on the oxidative deamination. Moreover, melatonin injected in pinealectomized rats derives in a more extended effect than pinealectomy and induces a stimulation of 5-HT synthesis in the striatum, probably due to a pharmacological effect. These results point to the striatum as a target area for the interaction between pineal melatonin and the serotonergic function, and suggest a differential effect of the melatonin injected on areas containing serotonergic terminals and cell bodies, which may relevant for the mode of action of melatonin and its behavioral effects.
Not exactly the most conclusive data, but it seems to indicate that yes, exogenous melatonin has the potential to increase serotonin the brain.