The first-night effect and the consistency of short sleep in insomnia disorder

The nature and degree of objective sleep impairments in insomnia disorder remain unclear. This issue is complicated further by potential changes in sleep architecture on the first compared with subsequent nights in the laboratory. Evidence regarding differential first-night effects in people with insomnia disorder and controls is mixed. Here, we aimed to further characterize insomnia- and night-related differences in sleep architecture. A comprehensive set of 26 sleep variables was derived from two consecutive nights of polysomnography in 61 age-matched patients with insomnia and 61 good sleeper controls. People with insomnia expressed consistently poorer sleep than controls on several variables during both nights. While poorer sleep during the first night was observed in both groups, there were qualitative differences regarding the specific sleep variables expressing a first-night effect. Short sleep (total sleep time < 6 hr) was more likely during the first night and in insomnia, although approximately 40% of patients with insomnia presenting with short sleep on night 1 no longer met this criterion on night 2, which is important given the notion of short-sleeping insomnia as a robust subtype.

Automated summary

The nature and degree of objective sleep impairments in insomnia disorder are still unclear. Changes in sleep architecture on the first compared with subsequent nights in the laboratory further complicate this issue. There is mixed evidence regarding differential first-night effects in people with insomnia disorder and controls. This study aims to characterize insomnia- and night-related differences in sleep architecture. People with insomnia consistently had poorer sleep than controls on multiple variables during both nights. Although short sleep was more likely during the first night and in insomnia, a significant number of patients with insomnia no longer met this criterion on the second night, highlighting the importance of considering short-sleeping insomnia as a subtype.