Longitudinal changes in insomnia status and incidence of physical, emotional, or mixed impairment in postmenopausal women participating in the Women's Health Initiative (WHI) study.

Objectives/background: We assessed prevalence and correlates of insomnia; associations between changes in insomnia with incidence of physical, emotional, and mixed impairments (PI, EI, and MI, respectively); and age as a moderator in these relationships.
Participants/methods: The Women's Health Initiative (WHI) clinical trial (CT) and observational study (OS) cohorts with 1- and 3-year follow-ups, respectively, were studied. Participants included 39,864 CT and 53,668 OS postmenopausal women free of PI or EI at baseline. Insomnia Rating Scale (IRS), with a cutoff score of ≥9 indicated insomnia. Normal-Normal, Abnormal-Abnormal, Normal-Abnormal, and Abnormal-Normal categories indicated change in insomnia over time. PI, EI, and MI were constructed using Short Form-36 (SF-36) Physical and Emotional subscales (cutoff ≤60) and the modified Center for Epidemiological Studies Depression scale (cutoff ≤0.06).
Results: Among 93,532 women, 24.5% had insomnia at baseline. The highest odds ratios (ORs) for impairments were found in the Normal-Abnormal and Abnormal-Abnormal categories. In the CT cohort, Normal-Abnormal category, ORs were 1.86 (95% CI = 1.57-2.20) for PI, 4.11 (95% CI = 3.59-4.72) for EI, and 6.37 (95% CI = 4.65-8.74) for MI. Respective ORs for the OS cohort were 1.70 (95% CI = 1.51-1.89), 3.80 (95% CI = 3.39-4.25), and 4.41 (95% CI = 3.56-5.46). Interactions between changes in insomnia and age showed distinct albeit nonsignificant patterns.
Conclusions: The results suggest that exposure to insomnia increases vulnerability to impairment. Future studies are needed to understand the directionality of these relationships.
(Copyright © 2014 Elsevier B.V. All rights reserved.)