| Good sleep quality is effective in preventing premature ageing, as demonstrated in a pioneering study that found that sleep deprivation had a detrimental effect on metabolism, endocrine function (Spiegel, Leproult, & Van Cauter, 1999), cognitive functions (Ballesio & Lombardo, 2016), health status (Rayward, Duncan, Brown, Plotnikoff, & Burton, 2017), life satisfaction (Zhi et al., 2016), and others. This means that sleep insufficiency can worsen chronic health problems related to age (Quevedo-Blasco, Zych, & Buela-Casal, 2014; Spiegel et al., 1999). That is, sleep strongly influences many aspects of health (physical, cognitive, and emotion health) and its restriction may predispose a person to adverse health conditions (Hirshkowitz et al., 2015). Thus, sleep insufficiency is a variable of great importance when considering older adults, because it may impact several domains, such as attention impairments, slowed response time, memory and concentration impairments, decreased ability to accomplish daily tasks, and increased risk of falling (Abraham, Pu, Schleiden, & Albert, 2017). Having in account that the World Health Organization, WHO (2015) expects an increase from the current 841 million to 2 billion of the world’s population to be over 60 years old by 2050, elderly well-being is a challenge to global public health. Unfortunately, the fact that elderly individuals live longer is not necessarily related to their quality of life; many these individuals depend on medication and medical and welfare care (WHO, 2015). This shows the importance of increasing research efforts to explore how the health of older adults is affected by issues such as the sleep quality. Therefore, there must be a better understanding of the multitude of factors impacting sleep satisfaction to improve sleep quality in older adults (Abraham et al., 2017) and promote health and quality of life. The negative impact of sleep insufficiency and poor sleep quality has been observed and demonstrated in the physical, emotional, mental, and social domains of life, both on a short- and long-term basis (Gottlieb et al., 2005; Quevedo-Blasco et al., 2014; World Association of Sleep Medicine, 2016). There is also empirical evidence that shows a negative impact of the above-mentioned aspects on psychological disorders, such as depression, anxiety, and psychosis (Ballesio & Lombardo, 2016; Quevedo-Blasco et al., 2014). Therefore, emotion and sleep have been shown to be closely related, this issue is increasingly recognized as an important area of research (World Association of Sleep Medicine, 2016). In addition, the relationship between sleep and emotions has been demonstrated as bi-directional and is reported by Kahn, Sheppes, and Sadeh (2013, p. 225) as a ‘‘vicious cycle’’. Sleep tends to compromise emotional regulation, which in many cases leads to an increase in negative emotions and interrupts sleep, leading to new deficiencies in emotional well-being and life satisfaction (Kahn et al., 2013; Rayward et al., 2017). For this reason, further research is needed to understand the relationship between sleep and emotions, and the impact that this relationship may have on the quality of life. As such, this study tested a mediation hypothesis, through a path analysis, which could explain how depression relates to the quality of life considering the effects of sleep quality in older adults. This work aims to contribute to the knowledge about the relationship between sleep quality and depression, in order to assist in the development of interventions for the prevention of depression for older adults. |