Incidence, Persistence, and Remission Rates of Insomnia Over 5 Years

Abstract

Insomnia is a significant public health problem, but there is little information on its natural history. To assess the incidence, persistence, and remission rates of insomnia over a 5-year naturalistic follow-up period. This cohort study included participants with and without sleep problems selected from the adult population in Canada from August 2007 to June 2014. Participants completed an annual survey about their sleep and health status for 5 consecutive years. Using validated algorithms, participants were classified at each assessment as being good sleepers (n = 1717), having an insomnia disorder (n = 538), or having subsyndromal insomnia (n = 818). Survival analyses were used to derive incidence rates of new insomnia among the subgroup of good sleepers at baseline and persistence and remission rates among those with insomnia at baseline. Sleep trajectories were examined by looking at year-person transitions between each consecutive year summed over the 5-year follow-up period. All inferential analyses were weighted according to normalized sampling weights. The sample included 3073 adults (mean [SD] age, 48.1 [15.0] years; range, 18.0-95.0 years; 1910 [62.2%] female). Overall, 13.9% (95% CI, 11.0%-17. 5%) of initial good sleepers developed an insomnia syndrome during the 5-year follow-up period, and incidence rates were higher among women than among men (17.6% [95% CI, 13.6%-22.7%] vs 10.1% [95% CI, 6.6%-15.3%; χ2 = 4.43; P = .03). A total of 37.5% (95% CI, 32.6%-42.5%) of participants with insomnia at baseline reported insomnia persisting at each of the 5 annual follow-up times. For subsyndromal insomnia, rates were 62.5% at 1 year to 26.5% at 5 years. For syndromal insomnia, rates were 86.0% at 1 year to 59.1% at 5 years. Conversely, remission rates among those with subsyndromal insomnia were almost double the rates among those with an insomnia syndrome at 1 year (37.5% [95% CI, 31.7%-44.0%] vs 14.0% [95% CI, 9.3%-20.8%]), 3 years (62.7% [95% CI, 56.7%-68.7%] vs 27.6% [95% CI, 20.9%-35.9%]), and 5 years (73.6% [95% CI, 68.0%-78.9%%] vs 40.9% [95% CI, 32.7%-50.4%]). Yearly trajectories showed that individuals who were good sleepers at baseline were 4.2 (95% CI, 3.51-4.89) times more likely to stay good sleepers in the subsequent year, but once they developed insomnia, they were equally likely to report symptoms (47% probability) than to return to a good sleeper status (53% probability) 1 year later. Similarly, those with an insomnia syndrome at any given assessment were more likely (adjusted odds ratio, 1.60; 95% CI, 1.19-2.60) to remain in that status (persistence) than to improve (remittance) at the next assessment; even among those who improved, the odds of relapse were greater (adjusted odds ratio, 2.04; 95% CI, 1.23-3.37) than those to improve in the following year. The findings suggest that insomnia is often a persistent condition. Considering the long-term adverse outcomes associated with persistent insomnia, these findings may have important implication for the prognosis and management of insomnia.