بی خوابی و افسردگی: عوامل خطر برای توسعه افسردگی در مردان ژاپنی در طول 2011-2013 Insomnia and depression: risk factors for development of depression in male Japanese workers during 2011–2013

Introduction It is well known that depression is often accompanied by insomnia. On the other hand, recent researches have also shown that insomnia can be a risk for the development of depressive symptoms. In young adults, insomnia for more than 2 weeks was found to be a risk factor for future depression (Buysse et al. 2008). College students with insomnia symptoms had more mental health problems (depression, anxiety, etc.) than those without insomnia (Taylor et al. 2011). Elderly females with persistent insomnia were at increased risk for the development of new-onset depression (Perlis et al. 2006). In older adults aged 65 years or more, the risk of depression within the next 3 years was found to more than 3 times higher in those with insomnia (Riemann and Voderholzer 2003). In a community-based sample, people with insomnia were 9.82 times more likely to have depression than people who did not have insomnia (Taylor et al. 2005). In a 3-year followup study of community residents aged 65 years or more in Japan, the risk of developing depression was shown to be about 1.6 times higher, especially in those with difficulty falling asleep (Yokoyama et al. 2010). Nevertheless, a systematic review has indicated that the etiological relationship between insomnia and the risk for development of depression remains unclear (Alvaro et al. 2013). Moreover, there have been very few studies on the increased risk of future depression in workers who have insomnia. The number of workers today who need to take leaves of absence or be reassigned as a result of mental disorders with depression or other depressive symptoms is not negligible. Effective preventive mental health measures for depression are an urgent matter for society, but as yet no specific methods have been established. For workers, eliminating insomnia also has other beneficial effects in terms of preventing drowsiness and decreased activity during work, and promoting safety. Thus, clarification of the association between insomnia and depressive symptoms in workers are important. The aim of this 3-year cohort study was to clarify the association between insomnia and the development of depression in the future, and furthermore analyze the association between the severity of insomnia and the onset of depression among male workers.