Cognitive impairment is a syndrome that reduces mind or intellectual activity. Given that late life cognitive changes may not initially appear to directly affect daily living, the degeneration of cognitive function may be left undiagnosed or be diagnosed at later stages (1, 2). In recent years, the eye-catching prevalence of cognitive impairment has been expected to dramatically increase with rapid aging in China. Jia et al. reported a total of 38.77 million people aged 60 and more suffer from cognitive impairment, and the prevalence of cognitive impairment amongst older adults in China was 15.54% (3).

To make matters worse, the urban-rural inequality in cognitive health has been plaguing the Chinese government. Previous studies have demonstrated a widened urban-rural disparity in cognitive performance amongst older population in China. For example, Zhang et al. found that rural older adults suffered from more severe cognitive impairment due to inadequate access to healthcare (4). Sun et al. reported that urban older adults had better cognition than their rural counterparts (5). Tian et al. uncovered that rural older adults had worse psychological disorders compared with their urban counterpart (6). This cognitive disadvantage amongst rural residents is usually explained by the negative impacts of rural living, such as limited access to education, workforce participation and healthcare (7).

It is well known that China is a huge country with significant urban-rural differences in terms of social and economic circumstances. Large academic medical centers, tertiary hospitals and skilled medical practitioners are concentrated in urban areas, which resulted in the inequality of health services between rural older adults and their urban counterpart (8, 9). Limited health resources and unfavorable economic status hinder rural residents from receiving timely treatment for physical and mental illnesses (10, 11). Consequently, rural older adults suffer from disproportionately poorer health and worse health outcomes compared with urban older adults.

To eliminate the urban-rural disparity in healthcare, many strategies have been taken at the national level over the past decade. For example, healthcare resources were redistributed across rural areas since the new round of healthcare system reforms in 2009 (12). Urban Resident Basic Medical Insurance (URBMI) and New Cooperative Medical Scheme (NCMS) were integrated to reduce urban-rural inequality in access to health services (13). However, it remains unclear whether the gap between the cognitive health of urban and rural older adults is narrowing after these efforts, and which determinants contribute to such changes, if any, in rural-urban disparity in cognitive health. To our knowledge, no study has provided related empirical evidence to answer the above-mentioned questions, given that most studies only adopted a cross-sectional data, and time series econometric methods were rarely used.

This study aims to identify the dynamic changes in cognitive performance differentials between urban and rural older adults over a 10-year period (2008–2018) in China and further decomposes determinants affecting this change. To our knowledge, this is first study in China that focuses on the dynamic changes of urban-rural disparity in the cognitive ability of older adults. Findings of the study will shed some light on future priorities to further narrow the rural-urban disparity in health outcomes.

This study reveals a reduction in the cognitive performance of older adults' differentials between urban and rural older adults in China from 2008 to 2018. This change is attributable to the quantity and priced effects of various explanatory factors.

The change in the proportion of people ≥ 96 years between urban and rural significantly contributed to the decline in cognitive performance disparity. The underlying reason may be because the considerable investment in the rural health system in recent 10 years has increased the life expectancy of the rural population in China (23). These efforts balanced the share of older adults between urban and rural areas. Accordingly, age-related cognitive disorder disparity between urban and rural older adults are expected to be reduced as well.

Interestingly, an effect of homeownership gap on cognitive ability disparity in urban and rural seemingly decreased in the 2018 wave. The association of homeownership with cognitive health is mainly due to the mediation effects of the perceived sense of control, community trust and residential stability (24, 25). However, China's accelerated urbanization in the past period resulted in the increased number of old people who migrate from rural to urban with their children (26). Frequent mobility of residence reflects that owning a house at present does not mean an increased sense of control and stability for senior residents. Consequently, the effect of homeownership on the cognitive ability of older adults decreased accordingly in 2018 comparing with that in 2008.

Another encouraging finding is that the reduction in self-rated poor economic status amongst rural older adults positively contributed to the narrowed cognitive disorder differential. The rapid socioeconomic development in China over the past few decades significantly increased income growth in rural regions, and the establishment of a universal medical insurance system also decreased the out-of-pocket payment ratio for medical care (27, 28). Consequently, financial hardship was substantially reduced when rural older adults sought medical services, which further decreased exposure to the risk factors of cognitive impairment owing to timely treatments.

Our findings also reveal that an increased share of rural older adults who exercise regularly reduced the cognitive function inequality greatly between urban and rural. These findings were supported by previous studies reporting physical exercises can increase production of neurotrophic factors and cerebral blood flow, as well as further prevent degeneration of the brain's cognitive function with aging (29, 30). Furthermore, given that the Chinese central government increased investment in the basic rural healthcare infrastructure, and health education services were widely provided in rural areas in recent years, more older people are encouraged to take physical exercises, thus delaying the damage of cognitive decline. Moreover, the finding that price effect of trips declined over time might reflect other recreational activities in rural regions, such as Chinese chess and square dancing, which are often organized to improve the well-being of rural older adults, thereby offsetting the impact of the urban-rural inequality in travel participation.

A gap in proportion to the older adults who still worked during retirement age between urban and rural exacerbated the widening cognitive function disparity. A potential explanation can be attributed to the urban-rural gap in social security and welfare benefits. On the one hand, social security coverage in rural areas is much lower than that in urban areas, even though the Chinese government proposed the establishment of a rural endowment insurance system in 2009. On the other hand, the level of social security and welfare benefits rural older adults can receive is also quite limited because of the great urban-rural disparity in economic development (31, 32). Resultantly, rural older adults must work to earn income and thus endure more pressure from their jobs, which create an adverse effect on cognitive ability. Similarly, the quantity effects of pension and amount of social security also revealed that an unbalanced distribution of social security between urban and rural was expanding over time, which further caused the expansion of the cognitive function differentials. Prior studies have proved that expansions in social security and welfare benefits have important protective effects on mental illnesses, especially for disadvantaged groups, by providing additional income to increase financial security and reduce social status anxiety (33, 34). A large room exists for bridging the cognitive performance gap by improving social security coverage and welfare benefits for rural older adults.

Individual experiences in childhood can influence health and well-being in the late periods of life. Exposure to fetal malnutrition has considerable and long-lasting impacts on physical health and cognitive abilities (35). “Cognitive reserve” theory suggests that early education can delay manifestation of dementia symptoms in much older adults by allowing the brain to better cope with damages (36). In this study, the participants in our analysis were born before 1953. They endured the Great Famine and the Cultural Revolution in China, which led to malnutrition and poor education, especially in the rural group. Therefore, this study finds that rural older adults who suffered from hunger and poor education at a young age performed worse in cognitive ability, subsequently widening the urban-rural difference. Moreover, this impact intensifies over time. An implication from this evidence supported policies and programs to improve the nutritional status and education level for children at an early stage, especially in China's underdeveloped rural areas.

This study holds some limitations the must be acknowledged. Firstly, community- and provincial-level variables were not used to explore their contributions to the changes in the cognitive performance differences between urban older adults and rural older adults due to limited data, even though a comprehensive set of individual level variables was included on the basis of Lund's conceptual framework. Secondly, survival bias may exist, because the CLHLS focuses on the long lived, and the survey may exclude people who did not live long lives. Thus, a healthy sample can be presented, resulting in an underestimated cognitive impairment. Thirdly, data in CLHLS were collected by self-report. Recall bias and measurement bias should be paid an attention.

Although the urban-rural disparity in the cognitive performance of older adults in China narrowed from 2008 to 2018, it remains a significant problem. The rapid economic development and reform of the rural health system significantly contributed to the narrowed gap. However, then unbalanced distribution in social security and welfare between urban and rural regions resulted in an expanding trend in the urban-rural inequality of cognitive function. Additionally, future policy interventions must highlight rural older adults who suffered from hunger and limited education during childhood, because the negative effects of these hardships on cognitive function intensify late in life.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

The studies involving human participants were reviewed and approved by the Institutional Review Board, Duke University (Pro00062871), and the Biomedical Ethics Committee, Peking University (IRB00001052–13074). Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin.

TZ was responsible for the study design, implementation, and writing. BL collected and analyzed the data and reviewed and edited original draft. XW revised and critically commented the manuscript. All authors made significant contributions to this study and have read and approved the final manuscript.

This work was supported by National Natural Science Foundation of China (grant number: 71974050) and the Scientific Research Foundation for Scholars of HZNU (grant number: 4265C50221204120).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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