Decreased plasma orexin levels in subjects with impaired sleep quality

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The orexin system has been identified to play an important role in controlling arousal and regulation of sleep and wakefulness. An orexin deficit has been identified as the most important part of the pathophysiology of sleepiness in narcolepsy. Although orexin receptor blockade has been identified as a successful new treatment approach to insomnia, a disorder of hyper-arousal, no study has investigated whether orexin plasma levels are elevated in this disorder. In this investigation we analyzed the association between the orexin plasma levels and Sleep Quality (PSQI) scores in a sample of 259 subjects (18–55 [M = 33.4] years) from the general population and hypothesized poor sleepers to show higher orexin levels. Opposite to the hypothesis the global PSQI score correlates negatively with orexin levels (r = −.199, p = .002). Nearly one quarter (24.1%) of the sample was classified as poor sleepers (global PSQI score > 5). In poor sleepers a significantly lower plasma orexin level was found compared to good sleepers (p = .014). Further analysis revealed significant negative relationships between the plasma orexin levels and the PSQI component scores “subjective sleep quality” (r = −.140, p = .03) and “daytime dysfunction” (r = −.194, p = .002). Although a high percentage of the poor sleepers was most likely suffering from insomnia their probable hyperarousal did not appear to be associated with an increase in plasma orexin levels.