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19-05-2013 | Sleep medicine | Article

Nonrestorative sleep and insomnia differences clarified


Free abstract

medwireNews: Researchers have found substantial differences between nocturnal insomnia symptoms (NIS) and nonrestorative sleep (NRS), highlighting the heterogeneity of insomnia symptoms.

Clear differences were seen with regard to sociodemographic characteristics, sleep disorders and medical comorbidity, and functional impairment.

Kathleen Merikangas (National Institute of Mental Health, Bethesda, Maryland, USA) and team also found that patients with NRS were a significant 1.36 times more likely to have C-reactive protein (CRP) levels in the upper quintile than individuals without insomnia, whereas this was not the case for patients with NIS.

"This indicates that increased CRP level in NRS might be directly linked to the pathogenesis of NRS," say the researchers.

The team analyzed data from the 2005-2008 National Health and Nutrition Examination Survey (NHANES) on 10,908 individuals aged 20 years or older, 1983 of whom had NIS and/or NRS.

The 1-month prevalence estimates were 18.1% for any insomnia symptoms, 7.9% for NIS-only, 5.4% for NRS-only, and 4.8% for NIS plus NRS. Only about 26% of those with any insomnia symptoms had both NIS and NRS.

As reported in Sleep, the prevalence of NIS increased with age, whereas the prevalence of NRS decreased with age, when compared with controls without insomnia. Specifically, the prevalence of NIS was 6.6% in patients aged 20-29 years, increasing to 9.5% in those aged at least 60 years. The corresponding rates for NRS were 6.3% and 3.7%.

As well as tending to be older, patients with NIS generally had a lower family income and educational levels than those with NRS.

NRS was significantly associated with other primary sleep disorders, including sleep apnea (odds ratio [OR]=2.58) and habitual snoring (OR=1.50), compared with no insomnia, whereas no significant associations were seen for NIS.

"We speculate that NRS might be an integrated indicator of insufficient sleep quantity or sleep quality as induced by other sleep problems," says the team.

It was also significantly associated with comorbid respiratory conditions, such as emphysema (OR=1.93) and chronic bronchitis (OR=1.44), and cancer (OR=2.00). By contrast, NIS was significantly associated with cardiovascular diseases, such as congestive heart failure (OR=1.72) and coronary heart disease (OR=1.64).

"Our findings of the high comorbidity of medical conditions and sleep problems in the NRS-only group indicate that the management of other sleep problems and medical conditions might also benefit those with NRS symptoms and may consequently improve daytime functioning," say the researchers.

They note that, although patients with both NIS and NRS did not have more sleep problems or medical comorbidity, they did have substantially more functional impairment on the Functional Outcomes Sleep Questionnaire than controls and those with either symptom alone.

medwireNews ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013

By Lucy Piper, Senior medwireNews Reporter