Dementia is a progressive cognitive disorder characterized by a potential decline in cognitive function that commonly affects older adults and can have varying degrees of impact on the patient, to the point of disruption of daily life or even death (Writing Group of Expert Consensus on Long-term Healthcare of Cognitive Disorders in China, and Academy of Cognitive Disorder of China, 2016; Hill et al., 2017). Cognitive impairment can affect memory, learning, orientation, comprehension, judgment, calculation, language, visuospatial function, problem-analyzing, and solving abilities, and is often accompanied by psychiatric, behavioral, and personality abnormalities at some stage of the disease course (China Dementia and Cognitive Disorders Guidelines Writing Group, 2018a). Dementia can put a tremendous financial, mental, and physical strain on the patient and society.

The World Alzheimer Report 2015 shows that the prevalence of dementia was 46.8 million in 2015 and is expected to increase to 131.5 million by 2050, with most of the increase occurring in low and middle-income countries (Alzheimer’s Disease International et al., 2015). According to the latest estimates, China has the highest number of people with dementia in the world, with more than 15 million older adults having dementia, accounting for about 20% of the total number of people with dementia worldwide (Jia et al., 2020). The combined global cost of health care and lost revenue because of dementia has reached $81 billion per year and is expected to rise to $2.8 trillion by 2030 (Alzheimer’s Disease International, 2021). In a multicenter retrospective study for China, the annual socioeconomic burden of Alzheimer’s Disease (AD) for each patient amounted to $19,114.36 in 2015, with a total cost to society of $167.74 billion, equivalent to 1.47% of China’s domestic GDP, which is higher than the global average of 1.1% (Jia et al., 2018). It is foreseeable that, with the accelerated aging of the population, dementia will become a major public health problem in China in the future (Rizzi et al., 2014).

Dementia, as a central nervous system degenerative disease, is irreversible and currently has no effective cure, with a failure rate of 99.6% in clinical treatment trials over the past decade (Cummings et al., 2014). To prevent and intervene early in dementia, some scholars have proposed a precursor stage of dementia−mild cognitive impairment (MCI). MCI is defined as a progressive decline in memory or other cognitive functions but with essentially normal daily living skills and does not meet the diagnostic criteria for dementia (China Dementia and Cognitive Disorders Guidelines Writing Group, 2018b). MCI is likely to progress to dementia with attendant social and health impairment. Approximately 5−10% of MCI will progress to dementia each year and both MCI patients and those recovering from MCI have a higher risk of developing dementia than healthy older adults (Mitchell and Shiri-Feshki, 2009; Roberts et al., 2014). MCI is an intermediate state between normal cognition (NC) and dementia and neurological degeneration can still be reversed through neuroplasticity. Thus, interventions for MCI patients are of greater public health significance than for dementia patients (Huang et al., 2005).

Physical activity is an effective way for older adults to maintain their physical and mental health and is also inextricably linked to their cognitive function (Fan, 2019). The protective effect of moderate to vigorous physical activity on cognitive decline is significant (Guure et al., 2017). However, although different types of physical activity have different effects on cognitive function, there is a general paucity of related studies. Physical exercise and household chores have a protective effect on cognitive decline, but work-related activity has no significant effect on cognitive function (Dupré et al., 2019).

Mental health has a strong correlation with cognitive dysfunction such as MCI, and older adults with depression are at a higher risk of developing MCI (Li et al., 2018). Depression also has more influencing factors, such as gender, age, and education level. Among these factors, studies have confirmed that physical activity has a preventive effect on depression (Petersen, 2016). Both physical activity and depression have effects on cognitive function, and physical activity interacts with depression (Lindwall et al., 2011), this indicates that depression may play a mediating role in the effect of physical activity on cognitive function, which has been verified in a few studies (Spirduso, 2009; Vance et al., 2016).

However, the mediating mechanism of depression between physical activity and MCI is less explored in China and needs to be confirmed by more evidence. The purpose of this study is to understand the current situation of MCI among the community-dwelling older adults in Xinzhuang Town, Minhang District, Shanghai, China, as well as the physical activity and other possible risk factors for MCI. Additionally, it explores the mediating effect of depression between MCI and physical activity. Based on this, we aim to provide scientific and credible evidence for the prevention and early intervention of MCI to maintain older adults’ physical and mental health and improve their quality of life.

This cross-sectional study included 2,518 community-dwelling older adults to clarify the prevalence of MCI in the community, re-explore the factors influencing MCI, discover the relationship between different types of physical activity and MCI, as well as verify the partially mediating role of depression in the relationship between physical activity and MCI.

The AD-8 scale combined with the BADL scale was used to detect the prevalence of MCI in older adults; the results showed that the prevalence of MCI in older adults in Xinzhuang Township was 10.8%. The prevalence of MCI in most international studies is concentrated between 15 and 18% in developed countries such as the United States (Petersen et al., 2014), the United Kingdom (Richardson et al., 2019), and Germany (Luck et al., 2007), and the latest authoritative study in China reported a similar prevalence (15.5%) (Jia et al., 2020). Although the prevalence detected in this study was low compared to this interval, it was generally consistent with the interval of 6.1–30.4% in low and middle-income countries (McGrattan et al., 2021). The large difference in prevalence between this study and others may be due to variations in research methods, instruments, and criteria (Guo et al., 2019), or it may be that the older adults have difficulty in detecting symptoms of their cognitive decline, and therefore the detection rate is underestimated (Huang et al., 2005). Although this research showed a slightly lower prevalence of MCI among older adults in the Shanghai community than in other studies, the nearly 11% prevalence still needs to be taken seriously by the relevant authorities. According to the Shanghai Bureau of Statistics, the proportion of the household population aged 60 years and above in Shanghai has exceeded 35% as of 2019 (Shanghai Municipal Health Commission, 2020). The national level of aging will increase in the future, combined with the conversion rate of 53% of MCI progressing to dementia over 3 years, if effective early interventions are not taken, the future burden of dementia will be unimaginable (Hanninen et al., 2000). The current situation urgently requires the early identification of risk factors for MCI and effective interventions for those older adults who still have a chance of MCI reversal to cope with the serious challenges of upcoming aging.

This study found that age, education, diabetes, depression, and physical activity influenced MCI. Age is by far the greatest identified risk factor for cognitive impairment such as MCI (Dunne et al., 2021) and the prevalence of MCI increases significantly with advancing age. As the brain functions gradually decline with age, the accumulation of negative changes in brain structure and function predisposes older adults to an accelerated decline in cognitive function (Mozley et al., 1999; Fratiglioni et al., 2010). The effect of education on MCI was also observed in this study where older adults with higher levels of education were less likely to develop MCI, which aligns with previous studies (Sattler et al., 2012; Ding et al., 2015). This may be attributed to education’s ability to effectively increase the cognitive reserve in the brain, thus, allowing for more leeway in cognitive decline during old age (Mungas et al., 2018). Data from the China Quality of Life Development Report for the Elderly (2019) revealed that the number of older adults with elementary school education and below is extremely high in China, exceeding 70%. Therefore, it is important to design appropriate interventions for older adults with low education levels. This study found that people with diabetes had a higher risk of developing MCI, supporting the results obtained in other studies (Luchsinger et al., 2007; Cheng et al., 2012; Xiu et al., 2019). There is a strong link between blood supply and brain function (Galiano et al., 2020), and negative changes or shocks from this link are a key cause of MCI (Nelson et al., 2016). Here, diabetic hyperglycemia may negatively affect this link, accelerating cognitive decline in the brain (Yu et al., 2019). Numerous studies have shown that depression is a major risk factor for MCI in older adults (Geda et al., 2006; Li et al., 2018), and similar results were obtained in this study. Data from a prospective cohort in China showed that middle-aged and older adults who are depressed at baseline have a more rapid decline in cognitive status and that timely and effective prevention and treatment can reduce the decline in cognitive function (Yang et al., 2020). Depression and cognitive dysfunction often coexist in the same patient (Mukku et al., 2021), and one study found that geriatric depression and Alzheimer’s disease share three neurobiological features including neurodegeneration, cerebrovascular dysfunction, and elevated levels of neuroinflammation (Weisenbach et al., 2019).

Several previous studies have shown that physical activity reduces the risk of cognitive disorders such as MCI in older adults (Geda et al., 2010; Wang et al., 2013), and this study’s results are similar. Additionally, this study found that different types of physical activity also have a protective effect on MCI. Among them, physical exercise and household chores remained significant in protecting against MCI after adjusting for possible confounders and mutual adjustment of different types of physical activities. However, physical exercise became insignificant in a multifactorial analysis among older adults who were not fully independent, while the significance of work-related activity disappeared in the mutually adjusted multifactorial analysis and this result aligns with other studies (Dupré et al., 2019). The failure of work-related physical activity to provide comparable protection may be because although work is also a physical activity, it is seen as compulsory and motivated by others, and work does not distract people from stress or improve their sense of self-esteem but is more likely to bring stress (Asztalos et al., 2009). The impact of physical activity in older adults who are not fully independent was not significant in the multifactorial analysis. This may be because there were fewer individuals under stratification, resulting in insufficient statistical validity; thus, studies should be conducted for such older adults in the future. This study suggests a protective effect of household chores on cognitive function, which has been confirmed by many studies (Dupré et al., 2020b), including one showing that household/transportation-type physical activity significantly reduces the risk of dementia in older adults (Dupré et al., 2020a).

This study validated a potential partial mediating role of depression between physical activity and MCI, with the effect being approximately 6.67%, which is consistent with existing studies’ results (Vance et al., 2005; Spirduso, 2009). One study observed a physical activity-depression-cognitive function pathway with higher levels of physical activity being associated with fewer depressive symptoms, which, in turn, were associated with better cognitive performance (Vance et al., 2016). The observed mediating effect of depression was 23.8% in a Chinese study and is higher than in this study (Chen et al., 2018), possibly due to differences in the measurement instruments used. Further, the AD-8 scale used in this study was unable to provide information on the cognitive functioning subdomain; so, some information may have been missing. It has also been proposed that physical activity positively affects emotional, mental, and motivational states, while depression, for example, negatively affects such states, so the offsetting effect of the two reflects physical activity affecting cognitive function through depression (Spirduso, 2009). Many scholars also explore the influence of other psychosocial-behavioral mechanisms on the relationship between physical activity and cognitive function (Stillman et al., 2016), such as sleep and social support (Bherer et al., 2013; White et al., 2017), which should be the focus of future research.

This study has some limitations. First, it is a cross-sectional study and its inherent limitations make it necessary to be cautious about the causal and mediating effects of the study. A longitudinal cohort study may be considered in the future to clarify the causal association between physical activity and depression. Second, because the study used the AD-8 questionnaire to evaluate cognition in older adults, it was not possible to examine the influence factors on specific functional domains of cognition and this should be considered in the future. Third, this study took the form of self-report of physical activity, which may introduce varying degrees of recall bias. More accurate measurements of physical activity should be made in the future using objective measures. Finally, brain activity was not explored in this study and the effect of this aspect should be further considered.

This study found that people who are older, less educated, living alone, and suffering from diabetes are more likely to develop MCI. The results suggest that the focus should be on this vulnerable group. Further, they should be treated with specific attention to their physical and mental status, especially their cognitive status, and given more care and support outside of the conventional prevention and treatment measures. This study’s results showed that not only does physical exercise have a protective effect on the cognitive function of older adults but household chores also have a similar protective effect. Therefore, it is recommended to encourage different types of physical activities in older adults through various means. The present study also observed a mediating relationship between depression in physical activity and MCI, suggesting that older adults with depressive symptoms can reduce their risk of developing MCI through active physical activity interventions.

The datasets presented in this article are not readily available because Data sharing is not applicable to this article due to privacy restrictions. Requests to access the datasets should be directed to corresponding author.

The studies involving human participants were reviewed and approved by the Ethical Review Board of Fudan University (reference number: IRB#TYSQ 2019-2-03). The patients/participants provided their written informed consent to participate in this study.

XL and YJ contributed to methods, data curation, and writing – original draft preparation. FW and YW contributed to the research design, conceptualization, and writing – review and editing. TY, YY, and FY partially participated in the research design. WP, MW, XC, and ML participated in the data curation and investigation. All authors have read and approved the final version of the manuscript, and agreed with the order of authorship.