Musculoskeletal pain and insomnia among workers
Insomnia symptoms are the most common sleep complaint in many countries, affecting 10–25% of the general population. In the USA, insomnia affects about a third of the population (Ohayon, 2009). A study based on the National Health Interview Survey data estimated an increase in insomnia of around 8% over a 10-year period (2002–2012) (Ford et al., 2015). Participants with hypertension, chronic obstructive pulmonary disease, asthma and joint pain showed the greatest increase in prevalence (Ford et al., 2015). A recent study suggested that sleep disturbances can augment pain symptoms by changing the modulation of central pain and that treatment of insomnia could reduce pain (Smith et al., 2015). Nevertheless, it is still unknown whether insomnia precedes pain or not. Ohayon (2009) examined whether pre-existing chronic pain was a predictor for the development of insomnia. The relative risk of developing insomnia was 1.8 among individuals with chronic pain. The authors also investigated the reverse effect, i.e. whether insomnia symptoms were predictors for the development of chronic pain. The results of the study showed that the presence of insomnia was not significantly associated with chronic pain over a 3- year follow-up. On the other hand, another study found insomnia to be a risk factor for the development of pain in healthy individuals with no evidence of reverse causation (Agmon & Armon, 2014). Insomnia was also identified as a relevant sleep disturbance among shift workers, having been associated with functional and cognitive impairments generally found among this group (Belcher et al., 2015). In addition, in a study of 418 workers (51 night workers, 158 rotating shiftworkers and 209 day workers), insomnia was one of the predictors for chronic pain in rotating shiftworkers (Vallières et al., 2014). Notwithstanding, there is a lack of studies investigating the reverse effect despite pain complaints being relatively common among shiftworkers. A few studies have noted that shift workers diagnosed with shiftwork-related sleep disorder report musculoskeletal symptoms (Waage et al, 2009). Thus, pain may contribute to the insomnia observed in shift workers and/ or vice versa. In this context, the aim of the present study was to evaluate the role of working hours and type of occupation in the sleep–pain relationship.