Despite the numerous investigations carried out in relation to melatonin, there is a lack of knowledge about the specific melatonin secretion patterns in the diverse primary sleep disturbances. The objective of this study was to analyze the plasma melatonin concentrations in children with primary sleep disorders and the effects of melatonin therapy on their serum levels and their actigraphic sleep parameters.

Fourteen participants (nine girls; seven to 14 years old) diagnosed with diverse primary sleep disorders were recruited. Four different melatonin secretion patterns were identified: low plasma melatonin levels, absence of a circadian rhythm, advanced acrophase, and delayed acrophase. A placebo (one week) was administered followed by three months of melatonin therapy (3 mg/night). Urinary 6-sulfatoxymelatonin levels, 24-hour plasma melatonin concentrations, and a seven-day actigraphic record were collected after both treatments.

After melatonin therapy, a significant increase (P < 0.001) of urinary 6-sulfatoxymelatonin excretion with a clear circadian variation was observed. Plasma melatonin concentrations were also significantly higher with a recovery in the circadian rhythm. Actual sleep time was significantly longer, with a substantial reduction in the sleep onset latency and night awakenings. No severe side effects were reported.

The main clinical implication of this study is to demonstrate the efficacy of melatonin in three main circumstances: an insufficient hormone production, a disturbed circadian rhythm, and an advanced or delayed acrophase. As ongoing work, we are exploring the effect of different doses of melatonin on the regulation of its concentrations and of its secretion rhythm.