1. Analysis on the prevalence of MCI among urban and rural residents in Datong:
Recently, China is rapidly stepping into a serious aging society. In 2020, the number of the elderly aged ≥60 in China is nearly 250 million. The population aged over 65 in China is expected to reach 338 million by 2050, and the number of the elderly aged over 80 exceeds 100 million [20]. With aging population in China, the prevalence of MCI is also increasing year by year, and the elderly may develop into dementia after MCI[21]. Studies have predicted that China's dementia population will reach 23.3 million by 2030, and the total cost of dementia is expected to be $ 114.2 billion by 2030, placing a heavy burden on families and society [22]. Enhancing the early identification and intervention for MCI patients can be effective approach to delay the progress of cognitive dysfunction in MCI patients and prevent MCI from progressing to dementia condition [23]. There are no specific drugs for AD treatment. Therefore, early detection and active prevention of AD are particularly important [24].
Several MCI studies conducted in elderly population of China are regional hospital surveys. The results showed that the prevalence of MCI varies between 3 % to 26.4 % [25-27]. There are few studies reporting the prevalence trend and distribution of MCI in the elderly population based on the overall investigation of county-level administrative divisions in China. Due to China's vast territory and different economic, social and cultural environment, these factors can lead to the prevalence of cognitive impairment in the elderly in different regions. Therefore, taking county-level administrative divisions as a unit, the investigation and analysis of the prevalence rate and development trend of MCI among the elderly in China can provide data support for relevant scientific researchers and departments to carry out research and implementation of public service policies for the elderly.
A study in Beijing reported that the prevalence of MCI in the elderly population in Haidian District of Beijing was 8.8%[28]. An epidemiological survey of MCI among the elderly over 60 years old in urban and rural areas of Guangdong Province found that the prevalence rate of MCI was 14.95%[29]. A study in Xiamen showed that the prevalence of MCI among the elderly in Xiamen was 20.14%[30] . A large sample study of elderly people over 60 years of age in 22 provinces across the country showed that the prevalence of MCI was 26.4%[31] . The results of our study showed that the total prevalence of MCI in urban and rural residents in Datong was 13.98 %, which was consistent with the results of other studies in China, suggesting that the total prevalence of MCI in urban and rural residents in Datong was basically consistent with the epidemiological characteristics of MCI in China.
The prevalence of MCI is closely related to residence. A study of urban and rural residents in Jiangsu province showed that the prevalence of MCI in urban elderly men and women was 16.5% and 19.9%[32], respectively. Among the elderly living in rural communities, the prevalence rates of men and women reached 35.6% and 63.2%[33], respectively. The results also confirmed that the prevalence of MCI in rural elderly was significantly higher than that in urban elderly. The prevalence of MCI is closely related to chronic diseases. The prevalence of MCI in the elderly with chronic diseases is higher than that in the elderly without chronic diseases.
2. Analysis of influencing factors of MCI in urban and rural residents of Datong
2.1 Role of gender in MCI: There is no consistent conclusion on the relationship between MCI and gender. A study reported that there was no significant difference in the prevalence of MCI between gender groups in the elderly over 64 years old [34]. Another study showed that the average deterioration of cognitive scores in women (11.58±1.4) was significantly higher than that in men (6.87 ± 1.1) (P=0.006), suggesting that gender plays a significant role in the prevalence of MCI in the elderly [35]. A study from China show that the prevalence of MCI in males is lower than that in females [36]. Another study from United States showed that the incidence of MCI in males was significantly higher than that in females in subjects aged 70-89 years [37]. The results of our study showed that there was no significant difference in MCI prevalence between male and female groups in urban and rural areas. There was no significant difference in the prevalence of MCI between urban and rural areas with the same gender.
2.2 Role of different age groups of urban and rural residents in MCI: Studies have reported that age is a risk factor for MCI. With increasing age, the prevalence of MCI increased accordingly [38]. Our results showed that the prevalence of MCI in urban and rural elderly in Datong increases with age. Logistic regression analysis shows that age is a risk factor for the incidence of MCI in urban and rural elderly in Datong.
Compared with the prevalence rate of MCI in the same age group of urban and rural residents, the difference in the prevalence rate of MCI between urban and rural elderly in the age groups of 70-79 and 80-89 was statistically significant, and the difference in the age groups of 60-69 and above 90 was not statistically significant. We speculate the reasons, may be 60-69 this age group of the elderly more retirement, many people still adhere to work or field work, cognitive function is still reserves ; the elderly in the age group above 90 have been transferred to the stage of pension, and as the elderly, their health status is generally good. The prevalence of MCI in urban and rural residents in70-79,80-89 age differences were statistically significant, may be due to less material and cultural life in rural areas, less mental pressure, relatively simple social environment, social life [39]. The results of our study showed that the prevalence of MCI in the elderly aged 70-79 increased significantly, suggesting that the elderly after 70 may be the turning point of the difference in the prevalence of MCI between urban and rural residents. We need to prevent MCI and AD early.
2.3 Role of education, residence and chronic diseases in MCI: The role of educational level or years of education in the occurrence of mild cognitive impairment is obvious. The elderly with higher educational level or longer years of education have lower risk of cognitive impairment [40-42]. The results showed that the prevalence of MCI in the elderly with different educational levels living in the same residence decreased with the increase of educational level, and the difference was statistically significant. Logistic regression analysis showed that high education level was the protective factor for MCI. High degree of education or learning age of the elderly due to regular learning, memory, thinking, could enhance the occurrence of neuronal synaptic connections, neurobiological function than the low degree of education and low years of education of the elderly. At the same time, high degree of education and years of education of the elderly to participate in social activities are beneficial to improve the reserve of cognitive function, increase the ability to compensate for cognitive decline, and develops a conducive environment to prevent cognitive dysfunction and AD in the elderly[43]. Therefore, elderly should strengthen the cognitive function reserve, effectively to prevent cognitive impairment in the elderly or delay the progress of cognitive dysfunction, and even make the elderly from MCI to normal aging.
Compared with the same population with the same educational level in the same place of residence, only the middle school education group showed significant differences, and there was no significant difference between other groups. Residents over 60 years old in urban areas of Datong are technically workers before retirement. After graduating from middle school, they have enrolled in various technical schools for 2-3 years, and the learning year is higher than that of ordinary middle schools.
In recent years, the impact of chronic diseases on cognitive function in the elderly has attracted more and more attention. Seveal studies have confirmed that chronic diseases have become the main risk factors for cognitive decline in the elderly [44,45]. Our study observed that the prevalence of MCI in urban and rural residents with chronic diseases in Datong was higher than that in the non-chronic diseases group, and the difference was significant. Chronic diseases might have become the main risk factor for health status, especially for the elderly.