Electroencephalographic sleep and natural killer activity in depressed patients and control subjects.

Insomnia is associated with a reduction of natural killer (NK) activity in depression independent of the severity of other depressive symptoms. This study extends these findings by exploring the relationship between objective electroencephalographic (EEG) assessment of sleep and values of NK activity in depressed patients (n = 23) and in control subjects (n = 17). The sleep EEG parameters total sleep time, sleep efficiency, and duration of nonREM sleep were each positively correlated with NK activity in the depressed patients and in the control subjects, demonstrating similar relationships between the amount of sleep and NK activity in the separate groups. These observations support the hypothesis that sleep measures are associated with NK cytotoxicity, independent of the effects of severity of depressive symptoms or the presence of a mood disorder.