The longitudinal course of insomnia symptoms: inequalities by sex and occupational class among two different age cohorts followed for 20 years in the west of Scotland.

STUDY OBJECTIVES: The natural history of insomnia symptomatology is poorly understood. Cross-sectional associations have been demonstrated among socioeconomic disadvantage, female sex, and poor sleep but it is unclear how these social factors predict patterns of insomnia symptoms over time. The aim of this article is to describe longitudinal patterns of insomnia symptoms as people age and investigate how they vary by sex and occupational class. DESIGN: A prospective cohort study with 20 yr of follow-up from 1987 to 1988. SETTING: West of Scotland. PARTICIPANTS: One cohort approximately 36 yr of age at baseline aging to 57 yr (n = 1,444), and another aging from approximately 56 to 76 yr (n = 1,551). INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: At approximately 5-yr intervals, respondents self-reported trouble initiating and maintaining sleep. Latent class analysis identified 4 main sleep patterns: a healthy pattern with little sleeping trouble across the 20 yr; an episodic pattern, characterized by trouble maintaining sleep; a chronic pattern with trouble maintaining and initiating sleep throughout the study; and a pattern where symptoms developed during the 20-yr follow-up. Chronic patterns were more likely in the older cohort than the younger one, for women than men in the older cohort, and for those from a manual rather than a nonmanual occupational class in both cohorts. In the middle-aged cohort a developing pattern was more likely for women than men. CONCLUSIONS: Chronic symptoms, characterized by both trouble maintaining and initiating sleep, are patterned by social factors.