The natural history of insomnia: high sleep reactivity interacts with greater life stress to predict the onset of acute insomnia.

STUDY OBJECTIVES: Prior research suggests that some individuals have a predisposition to experience insomnia following acute stressors (i.e. sleep reactivity). The present study was a proof of concept and specifically aimed to provide additional empirical evidence that the link between stressful life events and the onset of acute insomnia is moderated by sleep reactivity. METHODS: About 1,225 adults with a history of good sleep (Mage = 53.2 years, 68% female, 83% white) were recruited nationwide for an online study on sleep health. Participants completed surveys to assess sleep reactivity (baseline), sleep patterns (daily sleep diary), and stressful life events (weekly survey). All daily and weekly measures were completed for a one-year period. Sleep diary data were used to identify sleep initiation/maintenance difficulties, including whether they met criteria for acute insomnia at any point during the one-year interval. RESULTS: Participants with high sleep reactivity compared to low sleep reactivity were at 76% increased odds of developing acute insomnia during the one-year interval. In general, greater weekly stressful life events were associated with greater insomnia during the subsequent week. Those participants with high sleep reactivity demonstrated a stronger relationship between weekly stressful life events and insomnia, such that they reported the greatest levels of insomnia following weeks where they experienced a greater number of stressful life events. CONCLUSIONS: These results further support the sleep reactivity model of insomnia, and specifically, provide evidence that sleep reactivity predicts the incidence of acute insomnia in a sample of participants with no history of insomnia.

Age-dependent associations among insomnia, depression, and inflammation in nurses.

OBJECTIVE: Insomnia and depression have been inconsistently associated with inflammation. Age may be one important moderator of these associations. This study examined associations between insomnia and depression with inflammatory biomarkers in nurses and how these associations varied by age. Design: Participants were 392 nurses ages 18-65 (Mage = 39.54 years ± 11.15, 92% female) recruited from two hospitals. Main outcome measures: Participants completed surveys to assess insomnia and depression symptoms. Serum samples were obtained and analysed for inflammatory biomarkers interleukin-6 (IL-6), C-reactive protein (CRP), interleukin-1 beta (IL-1ß), and tumour necrosis factor alpha (TNF-α). Results: Neither insomnia nor depression symptoms were associated with inflammatory biomarkers. Older age was associated with higher IL-1ß, and age moderated the effects of depression symptoms on CRP and TNF-α: Greater depression symptoms were associated with higher CRP (b = .14, p = .017) and TNF-α (b = .008, p = .165) among older nurses only. Conclusion: Results suggest older nurses with higher depression symptoms may be at increased risk for elevated inflammation. Interventions should consider the role of age-related processes in modifying health and well-being. Given relatively low levels of depression in the current sample, future studies should replicate results in clinical and non-nurse samples.