Melatonin concentration as a marker of the circadian phase in patients with obstructive sleep apnoea

The effects of obstructive sleep apnoea (OSA) on the markers of glucose metabolism and other hormones are of interest, particularly since there is growing evidence that OSA may be a risk factor for disorders such as insulin resistance. However, interpreting these studies depends on the target hormone not having a diurnal rhythm and the circadian rhythm not being altered by the sleep fragmentation that occurs in OSA. Therefore, the aim of our study was to test the hypothesis that OSA displaces the circadian rhythm.

We carried out a prospective, observational, controlled, parallel study in 22 OSA patients (mean [SD] age: 45.1 [8.8]years; apnoea/hypopnoea index (AHI): 37 [24] events/h) and 22 age matched healthy subjects (age: 47.9 [7.9]years; AHI: 3 [1] events/h). Saliva samples for the measurement of melatonin were collected from participants resting in dim light at 30 min intervals between 19:30 and 22:30 h. Dim light melatonin onset (DLMO), a marker of the circadian phase, was taken at the end of the 30 min interval in which the greatest rise in melatonin occurred.

The group median (interquartile range) DLMO did not differ in OSA patients compared to healthy subjects (OSA patients: 90 [60-150]min; healthy subjects: 135 [90-150]min, p=0.19).

The circadian phase is the same in OSA patients and healthy subjects using salivary melatonin concentration as a marker of the circadian phase.