Differentiating nonrestorative sleep from nocturnal insomnia symptoms: demographic, clinical, inflammatory, and functional correlates

Abstract

Study objectives: Recent studies have suggested that nonrestorative sleep (NRS) symptoms may be distinct from nocturnal insomnia symptoms (NIS). However, there is limited information on the demographic, medical, and biologic correlates of NRS independent from NIS in the general population. This report presents the sociodemographic correlates, patterns of comorbidity with other sleep and physical disorders, C-reactive protein (CRP) levels, and general productivity associated with NIS and NRS in a nationally representative sample of US adults.

Design: National Health and Nutrition Examination Survey (NHANES).

Setting: The 2005-2008 surveys of the general population in the United States.

Participants: There were 10,908 individuals (20 years or older).

Interventions: N/A.

Measurements and results: Respondents were classified by the presence or absence of NIS and NRS. Compared with those without insomnia symptoms, respondents with NIS were older and had lower family income and educational levels than those with NRS. In addition, there was a significant association between NIS and cardiovascular disease, whereas NRS was associated with other primary sleep disorders (including habitual snoring, sleep apnea, and restless legs syndrome), respiratory diseases (emphysema and chronic bronchitis), thyroid disease, and cancer as well as increased CRP levels. In addition, the study participants with NRS only reported poorer scores on the Functional Outcomes of Sleep Questionnaire (FOSQ) than those without insomnia symptoms or those with NIS only.

Conclusions: These findings suggest that there are substantial differences between NIS and NRS in terms of sociodemographic factors, comorbidity with other sleep and physical disorders, increased CRP level, and functional impairment. An inflammatory response might play a unique role in the pathogenesis of NRS.

Keywords: C-reactive protein; functional impairment; medical condition; nocturnal insomnia symptoms; nonrestorative sleep..

Figure 1

Comparison of mean C-reactive protein levels (mg/dL) across groups. Nocturnal insomnia symptoms include difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening. *P < 0.05 significant difference when compared with normal sleep. ^$P < 0.10 when compared with normal sleep. ^&Significant difference between NIS-only and NIS + NRS. Model 1 adjusted for age, sex, poverty income ratio, ethnicity, educational level, and marital status. Model 2 adjusted for age, sex, poverty income ratio, ethnicity, educational level, marital status, Patient Health Questionnaire (PHQ-9) total score, body mass index, sleep duration, any cardiovascular disease, arthritis, lifetime smoking, clinician-diagnosed sleep apnea, habitual sleeping pill use, habitual snoring, and restless legs syndrome. Error bars = SEM.

Figure 2

Comparison in mean Functional Outcomes of Sleep Questionnaire general productivity scores across groups. Nocturnal insomnia symptoms include difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening. ***P < 0.001 when compared with any other group. ^#No statistically significant difference between normal sleep and nocturnal insomnia symptoms only (P = 0.670). Multivariable analysis was adjusted for age, sex, poverty income ratio, ethnicity, educational level, marital status, habitual sleep duration, habitual snoring, PHQ-9, lifetime smoking, clinician-diagnosed sleep apnea, restless legs syndrome, habitual sleeping pill use, and number of medical conditions. Error bars = SEM.