The authors measured serum levels of melatonin, a hormone secreted by the pineal gland which usually increases before and during nighttime sleep and falls markedly during daytime waking. They measured afternoon levels, expected to be low, in a group of 49 patients with OBSTRUCTIVE SLEEP APNEA prior to treatment, and compared results with those of 10 healthy non-snorers of similar age and sex. OBSTRUCTIVE SLEEP APNEA patients had significantly higher afternoon melatonin levels than controls--8.4 vs. 5.0 picograms per milliliter. Patients also showed much more variability in levels than controls; two patients showed levels 5-6 times normal.

This small, simple study gains importance for being apparently the first to investigate melatonin secretion in patients with OSA. Melatonin secretion has been seen as a "biological clock" mechanism, which turns on in the evening and virtually ceases throughout the day. Therefore it may have some causal relationship with triggering sleep onset. Melatonin, sold widely as a "food additive," clearly has pharmacological effects of causing sleepiness, at least when taken at certain times of the day, and altering the timing of the daily rhythm of the body. The occurrence of such high levels of melatonin in the afternoon as these researchers observed in patients with OBSTRUCTIVE SLEEP APNEA is unusual, suggesting disturbance of bodily cycles of sleeping and waking. It will be of great interest to see how these elevated levels change during the course of a day and whether they are related to timing of maximal sleepiness and likelihood of naps.

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