We measured the level of healthy aging by an index (healthy aging score) that integrates the physiological, psychological, and cognitive functional states of the population. Through a latent growth mixture model, an irreversible decreasing trend with age was found, and this decreasing trend differed between urban and rural areas, with a higher proportion of high-risk individuals presenting unsuccessful aging in rural areas. Multivariate logistic regression further proved that rural populations were more likely to develop high risk. Concentration indices and concentration curves showed that the lower the consumption level was, the higher the risk of becoming unhealthy, thus verifying the existence of inequity in healthy aging between urban and rural areas.
Healthy aging is a prominent objective in the development of a country, and rural-urban disparities are an essential obstacle to overcome. In China, the inequity of healthy aging between rural and urban areas is significant. Although the trajectory of being unhealthy is irreversible for older adults, the risk of unsuccessful aging is much higher in rural areas than in urban areas. It is caused by socioeconomic level, family structure, demographic characteristics, public resources etc. Based on our study, older adults with higher levels of education are less likely to develop high risk than those who have not received higher education. Relevant studies have shown that higher levels of education are associated with longer lifespans and delayed disease onset . People with higher education may have higher socioeconomic status, resulting in increased life satisfaction . People who are still working are less likely to develop high risk, which may be related to the fact that those who work are responsible for the family and are generally a source of income, and there is a significant positive gradient between life satisfaction and finances . Furthermore, the empty nest phenomenon is widespread in China, which means that there are a large number of elderly people who lack support because of the absence of children . Rural respondents are more likely to lack support, including economic support and emotional support, which has been proven to be significantly associated with the physical and psychological health of the older population . People who are involved in social life are less likely to develop a high risk, related to the environmental factors in which they live . We should encourage older people to participate more in social activities to develop a good environment and outlook. In addition, based on previous studies, we found that there are differences between urban and rural areas in terms of basic health status  and resources that can be accessed for medical services , which are the reasons for the differences in healthy aging between urban and rural areas.
According to our study, we know that income level is an important cause of the difference in healthy aging between urban and rural areas. In general, there is a link between income level and consumption level, and the higher the income level is, the higher the consumption level . According to the concentration index curve as income increases, the healthy aging score increases, indicating that income level has an effect on healthy aging. Related studies have shown that the rich have better health status than the poor in terms of self-assessed health , health-related quality of life , and individual height-for-age z-scores . Despite their higher level of need, the poor typically receive less health care than the better-off [43, 44]. The great disparity of income level between urban and rural areas still exists, and therefore, income levels affect the differences in aging between urban and rural areas, with healthy aging being better among urban older adults than among rural older adults.
By clarifying the differences in healthy aging between urban and rural areas and finding the factors that influence the differences between urban and rural areas, we can take more effective measures to reduce inequities. To alleviate the disparity in healthy aging between urban and rural areas, China has established a relatively well-developed social security system. However, this system still separates urban and rural areas and maintains a "dual-track" operation, and inequities remain. For this reason, it is important to balance the urban and rural economies, promote rural revitalization, and establish a national social security network to maintain efficiency and equity and alleviate the urban-rural healthy aging gap [43, 44]. Rural areas have low population density and large distances between homes and services . Health care facilities are difficult to operate, and the level of population health utilization is low. For this reason, rural infrastructure should be well developed. Finally, the older population should be encouraged to participate more in social activities, and a good social atmosphere should be formed by setting up clubs, promoting a diversity of activities, strengthening publicity and education for the older population in urban and rural communities, etc.
There are some limitations of this study. First, because our study used CHARLS data from respondents’ self-administered questionnaires, the results of the questionnaire depend on the respondents, and respondents may inevitably experience recall bias when filling out the questionnaire due to unclear recall and other reasons. Second, our study is a retrospective study, which cannot explore the relationship between urban-rural disparities and healthy aging trajectories in a deeper way. Third, when we compiled the CHARLS database, we found that many respondents did not provide income indicators, but we found a link between income and consumption, so we selected household consumption indicators when studying the impact of income level on the urban-rural healthy aging trajectory.