The present study revealed that LBP was associated with sleep disturbance, and this association was robust in participants with more frequent LBP episodes. Furthermore, antecedent LBP was associated with the onset of sleep disturbance, and the influence was stronger in participants with more frequent LBP episodes.
Sleep disturbance has been reported to coexist with LBP. [5, 6, 26, 27] Most of these studies have assessed sleep disturbance in patients with LBP. People with chronic LBP tend to have difficulty initiating sleep, reduced sleeping time, and lower sleep efficiency. [28] The rate of sleep disturbance among patients with chronic LBP was reported to be 50–60%. [6, 26] In the present study, 48.5% of the participants with LBP had sleep disturbance, even though LBP was not limited to chronic LBP; however, the rate was higher compared to 27.7% among the participants without LBP. Moreover, the association between LBP and sleep disturbances was significant after adjusting for potential confounding factors. Although several factors such as sex, age, and psychological and socioeconomic factors are associated with both LBP and sleep disturbance, [29,30,31,32] LBP is considered to be independently associated with sleep disturbance. In addition, previous studies have shown that LBP intensity correlates with the severity of sleep disturbance. [27, 33] These studies indicated that LBP and sleep disturbance are associated in a dose-dependent manner. Therefore, it is speculated that the frequency of LBP further affects the association between LBP and sleep disturbance. However, to the best of our knowledge, no study has assessed the association between LBP and sleep disturbance due to the frequency of LBP. The present study clearly showed that the association between LBP and sleep disturbance is stronger in patients with more frequent LBP. LBP is associated with sleep disturbance, and this association is considered robust among people with chronic LBP.
Regarding the causal relationship between LBP and sleep disturbance, some longitudinal studies have shown that antecedent sleep disturbance is associated with the onset of LBP among healthcare workers, [14] firefighters, [8] people after a natural disaster, [21] and the general population. [9] Additionally, other reports have shown that sleep disturbance is associated with poor recovery from pain in patients with LBP. [7, 12, 13] These reports indicate that sleep disturbance is a risk factor for LBP. However, only a few longitudinal studies have assessed the influence of LBP on sleep disturbances. Morelhão et al. reported that high LBP intensity in older patients was associated with poor sleep quality 6 months later. [10] The present study also showed that antecedent LBP was significantly associated with the onset of sleep disturbance 1 year later, even after adjustment for potential confounding factors. Although there have been only a few reports assessing the influence of pain on sleep disturbance, previous studies have shown that prior pain severity predicts subsequent sleep disturbance among patients with rheumatoid arthritis or orofacial pain. [34, 35] Furthermore, people with musculoskeletal pain, including LBP, would have a higher rate of sleep disturbance compared with those without the pain 1 year later. [19, 36] Regarding the influence of pain on sleep disturbance, it is hypothesized that pain prevents the initiation or continuation of sleep. [37] In addition, brain structure controlling nociception modulates sleep states, [38] and pain and sleep disturbance can occur due to a common neurobiological dysfunction. [37] A previous longitudinal study showed that preceding sleep disturbance was associated with onset of LBP, and the effect was stronger along with longer duration and increased frequency of sleep disturbance. [21] Conversely, the present study is the first to show that the influence of antecedent LBP on the onset of sleep disturbance is robust in participants with more frequent LBP. LBP leads to the onset of sleep disturbance in a dose-dependent manner, such as intensity [10] and frequency of LBP, as shown in this study. Sleep disturbance is considered a prospective symptom among people with LBP, and the onset of sleep disturbance can lead to poor recovery from LBP, [7, 13] and this interaction is assumed to be stronger dose-dependently. Understanding the mutual relationship between LBP and sleep disturbance is critical to prevent and treat these symptoms, especially focusing on chronicity.
This study has some limitations. First, LBP was assessed using a self-reported questionnaire, and pain was not quantified. The intensity of LBP is considered to affect sleep disturbance, which should be examined in future studies. Second, LBP and sleep disturbance were assessed at four time points over 3 years, and those for periods other than these time points were not clear, which may have affected the results. Finally, participants were people living in areas affected by the GEJE. Although 4 years have passed since the GEJE, the effects of the disaster may remain, and the generalizability of the results of the present study is not clarified.
In conclusion, LBP was associated with sleep disturbance among people living in places affected by the GEJE, and the association was robust in those with more frequent LBP. Furthermore, antecedent LBP was associated with the onset of sleep disturbance, and the effect was stronger in patients with more frequent LBP.