The results of the present study and investigation of 3948 people aged 50-90 years, the overall prevalence of severe depression in Iranian older adult was reported to be 8.2% based on a meta-analysis. Results of a meta-analysis study showed the overall prevalence of depression in the older adult was 43% in Iran between 2001 and 2015 [26]. A study in Sweden showed the prevalence of depression was 4.2% and the moderate-severe type was 1.6% [27]. A study in China also showed that the overall prevalence of depression in the older adult was 36.9%, and reported that the prevalence of symptoms was higher in women 50.4% as compared to men 33.3%. In general, the prevalence of moderate to severe depression was 3.9% in their study [28]. The prevalence of mild-moderate depression and mild-severe depression was reported to be 27%, and 12% in a study in Greek, respectively [29]. Another study in China reported that 26.5% and 4.4% of older adult people with depression had mild and severe depression, respectively [30].
Depression is often not diagnosed in the older adult and has important impacts on quality of life, clinical outcomes, functional status, medical services, mortality, and disability [31]. Depression in the older adult also leads to increased drug use, increase costs for drugs and over-the-counter drugs, higher risk of alcohol abuse, increased length of stay, and cost of care [32]. Depression occurs in the older adult, similar to younger people due to socio-psychological and biological factors [33]. Depression is a relapsing persistent disease, and risk factors for depression in older adult people include social isolation, marital status, divorce or separation, low socioeconomic status, debilitating comorbidities, insomnia, and functional and cognitive disorders [34].
Based on the results of various studies it was reported that depression in older adult had a significant relationship with married statues, satisfaction with place of living, use of medicine, living with spouse and children, emotional support of family, members, emotional support of friends, emotional support of others, satisfaction with relations and satisfaction with overall support [15, 19 and 23].
These studies also reported that Prevalence of mental disorders among older age, female, low education, marital status, activity, and income, unemployed and disabled older adult was significantly [19, 20, and 25]
Increased rates of depression in the older adult, especially the severe type reported in this study, are often neglected, making it difficult to diagnose and treat the disease in a timely manner. This is an unfortunate reality because depression is a disorder for which effective treatments are available today. The results of interventional studies Legrand et al [36] and Koshyar et al [37] were indicated in the reducing depression: regular physical activity and appropriate diet were Reduced the level of depression, These studies reported that both outdoors and indoors 15-min self-paced walks and Participating in enjoyable and pleasant exercises were associated with significant and positive affective, There is scientific agreement that exercise temporarily makes people feel more positively activated so that more frequent exercise may lead to a greater cumulative effect on positive affect and perhaps more opportunities to reduce negative thoughts and ruminative processes [36, 37].
It is also worth noting that the reduced mental ability and the feeling of sadness is not part of the normal aging process and this mood state should be considered important [34, 35]; therefore, considering the foregoing, screening and secondary prevention measures by nurses and healthcare providers are of great importance. Moreover, increasing families' awareness of depression in the older adult will also pave the way for early diagnosis and more appropriate treatment.
Limitations
The most important limitations of the current study include the lack of access to full text and the poor quality of some of the studies studied.