Purpose: Chronic low back pain is the number one cause for living with disability among 301 diseases and injuries analyzed by The Global Burden of Disease study 2013. Insomnia symptoms are highly prevalent in people with chronic low back pain, with 55-59% reporting symptoms such as poor sleep quality, non-restorative sleep, waking up too early, and difficulty initiating and maintaining sleep. For people with chronic low back pain, insomnia symptoms are associated with increased pain intensity and decreased physical function. People with insomnia have 1.36 times the odds of developing chronic low back pain 17 months later, compared to those without insomnia. To explain the sleep-pain relationship, theoretical models propose that activation of inflammatory markers such as tumor necrosis factor, interleukin 6, and high sensitive C-Reactive Protein (hsCRP), could contribute to increased pain, which may also further disrupt sleep. Of these inflammatory markers hsCRP is of interest as it has been commonly assessed in large population studies for cardiovascular disease risk. The relationship between insomnia and hsCRP, and the relationship between hsCRP and presence of chronic low back pain are not clear. This is partly due to the lack of consistent insomnia and chronic low back pain diagnostic criteria, other comorbidities or associated factors may not have been adequately controlled. Moreover, no study has modelled the associations of insomnia, hsCRP and chronic low back pain within the same sample We aimed to determine the associations between insomnia, chronic low back pain, and hsCRP, whilst controlling for age, body mass index, smoking, physical activity, depression, anxiety and osteoarthritis. Methods: A cross-sectional analysis of the third Nord-Trøndelag Health Study (2006-2008), a rural population survey of 50,666 participants in Norway aged 20-96 years. A comprehensive description of the data collection methodology has been published elsewhere. Insomnia (dichotomous) was defined according to the Diagnostic and Statistical Manual of Mental Disorders 5th Edition, and chronic low back pain (dichotomous) as low back pain or stiffness lasting at least three months. Data for hsCRP was obtained from non-fasting serum samples and assessed via latex immunoassay methodology. We excluded participants with the following self-reported chronic inflammatory diseases: chronic heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, fibromyalgia or ankylosing spondylosis. This was to ensure that our results reflected the possible associations of between insomnia, hsCRP and chronic low back pain and were not masked by these chronic inflammatory diseases. We compared the median hsCRP of these chronic inflammatory conditions to confirm their suitability for exclusion. Possible associations between presence of insomnia and presence of chronic low back pain (dependent), and the level of hsCRP and presence of chronic low back pain (dependent), were assessed using univariate logistic regression models. Possible association between insomnia and hsCRP (dependent) was assessed using linear regression. Multivariable analyses were conducted adjusting for confounders stated in our aim that achieved p ≤ 0.2 in univariate regressions. We performed stratified analyses for participants with normal (<3mg/L) and elevated (≥3mg/L) levels of hsCRP. Results: In our total included sample (n=30,669, median age 52.6, 54% female), 6.1% of participants reported insomnia (n=1,871), 21.4% had chronic low back pain (n=6,559), and 2.4% had both (n=719) (Figure 1). 24,288 (79.1%) participants had normal hsCRP while 6,429 (20.9%) had elevated hsCRP. Insomnia was associated with the presence of chronic low back pain (adjusted OR=1.99, 95%CI [1.79-2.21], <0.001) (Table 2). There was an association between hsCRP and presence of chronic low back pain (adjusted OR=1.01, [1.00-1.01], p=0.016) (Table 1). For participants with normal levels of hsCRP, insomnia was associated with hsCRP (adjusted B =0.04, 95%CI [0.00-0.08], p=0.037), but not for people within elevated levels of hsCRP (Table 2). Conclusions: In our large populational study, people with insomnia have double the odds of reporting chronic low back pain, and the role of high sensitive c-reactive protein in this relationship appears to be limited. Given the strong relationship between insomnia and chronic low back pain, it may be worth targeting these comorbidities as they may lead to improvements in the other. Longitudinal studies are required to explore whether the presence of insomnia and elevated hsCRP affects the development of chronic low back pain.View Large Image Figure ViewerDownload Hi-res image Download (PPT)
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