Introduction
ith the increase in the elderly population, the problems of this group are more emphasized [1]. In 2015, the number of people aged 60 years or older was about 900 million, and this number will reach about 2 billion by 2050 [2]. In 2016, the aging population of Iran comprised 9.28% of the total population and was estimated to reach 25%-30% by 2031 [3]. Sleep disorders are one of the problems related to old age [4]. Sleep is a complex and dynamic physiological state. Sleep deprivation causes neurological, autonomic, and biological changes. With aging, the prevalence of sleep problems increases [5]. Inability to sleep well at night can affect the quality of life; increase the risk of depression, anxiety, and stress [5, 6, 7]; and reduce cognitive function and concentration in dealing with daily activities [8]. The prevalence of sleep disorders in the elderly is 50%-70%, and the most common disorder is insomnia; 40% of people over 60 years of age complain of difficulty falling asleep or staying asleep [9]. Poor quality sleep, after headaches and digestive disorders, is the third most common problem in the elderly [6]. Sleep disorders can cause fatigue problems, headaches, impaired concentration, irritability, drowsiness, poor memory, unstable mood, increased response time and decreased performance levels [10]. These consequences expose the elderly to greater risks such as falls, cognitive and psychological disorders, poor physical function, decreased quality of life, increased dependence and vulnerability, and ultimately death [11]. Numerous factors such as gender, age, employment status, marital status, socio-economic status, place of residence, physical health, mental health, and nutritional status can be effective in causing sleep disorders, most important of which is age [12].
The Person-Environment-Occupation (PEO) model is a common and practical model in occupational therapy which consists of three domains of person, environment, and occupation. According to the Occupational Therapy Practice Framework (OTPF), the person domain includes all the characteristics that describe the unity of the person [13]. The environment domain includes cultural, institutional, virtual, physical, and social environments [13]. The occupation refers to a purposeful activity that is meaningful to a person and has value and importance. The mental and physical performance is always performed within a visible set of physical, social, and cultural conditions in the environment (workplace) and by a person with a developmental structure, goals, and unique meanings that have consequences for the environment. The result of a dynamic interaction between these components forms the function of occupation [14].
Due to the lack of a comprehensive study summarizing the mentioned factors and given the different prevalence rates of sleep disorders in the elderly in various countries (e.g. 35.9% in China [15], 23% in Germany [16], and 52.2% in Iran [17]), this study aims to review the negative factors affecting the sleep of Iranian elderly using the PEO model.
Materials and Methods
According to PRISMA (the Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, a systematic search was conducted on related studies published in English or Persian from 2010 to 2019 in Google Scholar, PubMed, Medline, Scopus, Magiran, IranMedex, and SID databases using the keywords of “Elderly”, “aging”, “geriatric”, “older adult”, “Iran”, and “sleep” in English and Persian. Studies on sleep problems of other age groups, letters to the editor, duplicate studies, studies on non-Iranian seniors, and studies published in languages other than Persian and English, and those with unavailable full-texts were excluded. Then, the titles and abstracts of the remaining studies were independently reviewed by two researchers. Afterward, the full text of all studies that met the inclusion criteria was retrieved. The full text of the selected articles was evaluated in terms of quality using the STROBE checklist (a tool designed for cross-sectional studies), and the articles approved based on at least 20 out of 22 items of the checklist were included in the study. Next, the data, including the number of samples, study location, measures, type of study, and sleep-disturbing factors, were extracted from eligible articles and recorded as shown in Figure 1.  The initial search yielded 235 articles. After checking the titles, this number was reduced to 44 due to the consideration of articles that examined the sleep quality of the elderly and the negative factors affecting it. Then, by reading the abstracts, 24 articles that were in line with the objectives of this research were selected for a deeper review.
Results
Negative factors affecting sleep quality in Iranian elderly were examined based on three PEO domains of person, environment, and occupation. Of 24 studies, 11 reported sleep problems in quantitative terms, of which 9 studies believed that more than 70% of the elderly had sleep problems. Eighteen studies reported personal factors that had a negative impact on the sleep quality of the elderly, and most studies addressed problems related to personal health (Figure 2). Eleven studies reported environmental factors with a negative impact on the sleep quality of the elderly, and most articles addressed problems related to the physical environment (Figure 2). In three articles, the factors that had a negative impact on the sleeping occupation of the elderly were reported; one study reported the “change in sleeping position”, and one indicated the factor of “talking before going to bed” (Figure 2). Among the reviewed studies, 8 (34%) had been conducted in 2017, 9 (37.5%) in Tehran City, Iran, and 95.83% used the Pittsburgh Sleep Quality Index (PSQI). Their total sample size was 3578 (mean number= 150, ranged from 30 to 400). Table 1 summarizes the reviewed studies regarding their participants, type of study, measures, and results.






Discussion and Conclusion
In the present study, the adverse factors affecting the sleep quality of the elderly were reviewed based on the PEO model, and the results of the studies were presented in three domains of person, environment, and occupation. Negative factors related to the domain of person included aging [18], female gender [19, 20, 21, 22], mental illness in older women and barriers and physical problems in older men [23], general health problems [21، 24, 25, 26], flushing [27], deficiency of minerals in the body, including magnesium [28], having chronic and underlying diseases [29], respiratory arrest [30], comorbid diseases [29], mental illness [27، 30, 31, 32, 33, 34], unrelieved pain [35], joint stiffness [36], knee pain [36], obesity [33], and lower education [33, 37]. The aging process is associated with objective and subjective changes in the quantity and quality of sleep. Therefore, complaints about difficulty in falling asleep and staying awake and drowsiness are more common in older people than in other age groups [18, 23]. Mental health problems were another factor. There is a correlation between depression and sleep disorder, and if the symptoms of depression are not treated, the quality of sleep will deteriorate significantly over time [23]. Chronic diseases such as diabetes were also one of the negative personal factors affecting the sleep of the elderly. Decreased overnight glucose tolerance is associated with decreased insulin sensitivity and insulin secretion response to elevated blood glucose [38]. Studies reported that women had more sleep problems and lower sleep quality than men, which is due to hormonal changes after menopause and being physiologically and psychologically sensitive [31].
Negative factors related to the domain of environment included being widow(ed), divorced or single [19, 39], poor economic level [37], living in a nursing home [40] and longer stay a nursing home [24 , 41], living in certain areas [40], unsuitable physical environment, excessive cold and heat, unpleasant noise [42] and excessive commuting in the resting place [40], light, sound and heat stimuli [35], lack of communication with relatives [27], lack of attention from others [43], feeling lonely [27], and high treatment costs [43]. The elderly who are sent to live in nursing homes lose the support of their family, leading to their depression, feelings of futility, physical problems, and social dysfunction, and affect the quantity and quality of their sleep [36، 44، 45]. The better sleep quality of married older adults than single, widowed, or divorced ones can be related to psychological and social factors. Married people have a great source of social support, i.e., family, while single and widowed people are deprived of this support [19، 39، 45].
Negative factors related to the domain of occupation included the change of sleeping place (e.g. spending a night as a guest in the house of children or relatives) [39], hospitalization [19], not talking to others before going to bed, unemployment [27], inactivity and prolonged lying down during the day [46], low quality of life [40, 47], lack of aerobic exercise [47], and dependence in performing basic and instrumental activities of daily living [48]. Retired and unemployed older adults have a higher risk of developing sleep problems. Retirement is usually accompanied by external pressures such as illness or the need to take care of a sick family member. It is associated with decreased physical and mental health due to loss of job and social relations and may turn a healthy adult into a weak person by reducing various physiological capacities and increasing susceptibility to many diseases. These processes and the development of mental illnesses such as depression, cognitive disorders, fear, and addiction, provide the basis for sleep disorders [49]. Lack of physical activity also affects the quantity and quality of sleep. Physical activity increases energy consumption and improves sleep quality by secreting endocrine. Sleep increases the secretion of anabolic hormones (e.g. growth hormone, testosterone, and prolactin) and reduces the levels of catabolic hormones (e.g. cortisol) [50]. The body’s metabolism and catabolic activity are increased during exercise to produce energy. Exercise is a stimulant to facilitate sleep and increase anabolic activity. Regular physical activity also increases physiological efficiency by reducing visceral fat and plays a role in deepening sleep. It increases the secretion of lactic acid in the body, which increases the body’s need for rest [49]. In three review studies conducted in other countries, the effect of cognitive performance [51], exercise [52], bright light, cognitive behavioral therapy, and movement exercises on sleep disorders in the elderly [53] have been indicated.
Personal factors such as age, female gender, chronic diseases, mental illness, and musculoskeletal disorders in the elderly are effective in causing sleep disorders in the Iranian elderly. Environmental factors such as Lack of communication with relatives and friends, inadequate physical environment, living in a nursing home, and the presence of sound, heat, and light stimuli also have adverse effects on their sleep. Finally, the factors of change of sleeping place, hospitalization, and not talking to others before going to bed are among the occupational factors that adversely affect sleep quality in the elderly. In intervention and counseling, therapists need to consider these personal, environmental, and occupational factors. Management approaches and training programs should be developed at different levels for the elderly.

Ethical Considerations
Compliance with ethical guidelines
This article is a meta-analysis with no human or animal sample. The present study is descriptive research (Code IR.UMSHA.REC.1398.746).

Funding
This study was extracted from a research project (with number 9809196978), financially supported by the Deputy for Research and Technology of Hamadan University of Medical Sciences.

Authors' contributions
All authors contributed equally in preparing this article.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank the Vice-Chancellor for Research and Technology of Hamadan University of Medical Sciences for their support.


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