Introduction

The 2018 revision of World Urbanisation Prospects reported that 55% of the world’s population lived in urban settlements, and it is expected to increase to 68% by 2050.1 A lion’s share of the future growth of the world’s urban population is expected to happen in low/middle-income nations.1 In advanced economies, city dwellers normally enjoy better living conditions, better healthcare access and more effective public-health interventions than their rural counterparts do. However, in low/middle-income countries, where urbanisation is rapid and unplanned, it is more likely to pose a threat to public health through environmental degradation, unhealthy lifestyles, increased stress and inadequate sanitation.2–5

China, the largest low/middle-income country in the world, has been undergoing urbanisation at an unprecedented rate over the last three decades.1 A small but growing body of literature has investigated the effect of urbanisation on the Chinese population’s health.6–15 Most earlier studies used either a single indicator (eg, urbanisation rate) or a composite indicator derived from a set of neighbourhood characteristics (eg, urbanicity index) to assess the level of urbanisation and explore its relationship with individual health.6–11 However, these studies have failed to recognise urbanisation as a multifaceted process involving population concentration, economic growth, land-use conversion, infrastructure upgrading, and lifestyle changes, and that different aspects of urbanisation may have complex effects on residents’ health.5 16–18 For example, the healthy migrant hypothesis suggests that a massive inflow of migrants to cities may improve the overall level of residents’ health.19 On the other hand, ‘salmon bias’ hypothesis implies that the unhealthy migrants who are retired or close to retirement age may return to their rural and small-town hometowns. A traditional Chinese aphorism is: ‘Fallen leaves return to the roots’ implying reverting to one’s origin. Economic growth and land-use change in rapidly industrialising countries are normally accompanied by increased environmental pollution, which is detrimental to residents’ health.2 3 12 20 21 On the other hand, economic growth may lead to better access to health knowledge and services, which could improve residents’ health.5 Lifestyle changes associated with urbanisation, such as less physical activity and more high-calorie food intake, may also affect residents’ health.8 22 23 Therefore, considering the effects of multiple dimensions of urbanisation on residents’ health could provide a complete picture of how urbanisation affects individual health.

Another limitation of previous studies is that the extent to which the urbanisation rate influences residents’ health has been rarely examined. For example, a previous study investigated the effect of living in more urbanised areas on health at a given time point (ie, urbanicity) in the Chinese context.6 8 However, highly urbanised areas do not necessarily experience rapid urbanisation.4 5 24 The rate of urbanisation also affects residents’ health, as a rapid urban growth is usually accompanied by environmental and behavioural transitions, such as environmental deterioration, increased stress, lifestyle change, changing population composition and declining social cohesion.2 4 5 8 22 25 Only a few studies have considered both the level and rate of urbanisation simultaneously. For example, Chen et al16 investigated the effects of urbanisation on health using multiple measures of urbanisation dynamics including the level and rate of urbanisation; however, their conclusion was drawn from the analysis of a small-scale survey conducted in 27 prefectures, which had the limitations of poor generalisability and homogeneous environmental settings.26 27 Therefore, including the rate of urbanisation in the analytical framework of urbanisation–health relationships is essential.

Another research gap is the lack of investigation into the moderating effect of individual attributes on urbanisation–health relationships. It is hypothesised that these relationships vary by education, as higher and lower educated people are likely to have different health practices and different levels of access to health services in large cities, whereas this educational gap is less pronounced in small towns and rural areas.28 29 It is also hypothesised that higher and lower educated people have differing propensities to migrate, and the effect of health selective migration varies by education level.30 Furthermore, higher and lower educated people differ in their ability to adapt to stress arising from rapid urbanisation and consequent social life changes.5 22 31 Therefore, the moderating effect of education on urbanisation–health relationships among older people is worth exploring.

This study aimed to investigate the association between urbanisation and self-rated health of older adults using the 2005 China’s 1% population sample survey and statistical data from statistical yearbooks. In particular, the study focused on how different dimensions of urbanisation (population growth, land-use change, economic growth and health service improvement) are related to older people’s health and how both the level and rate of urbanisation are associated with their health. Further, it examined the moderating effect of education on the association between each of the four dimensions of urbanisation and health. The study is significant in several respects. First, it considers the different dimensions of urbanisation, thus capturing the complex association between urbanisation and self-reported health (SRH) of the older adults. Second, it provides an in-depth understanding of the urbanisation–health relationship among older adults. Moreover, this study used nationally representative survey data covering 267 prefectures across 31 provinces, thus providing a more comprehensive picture of urbanisation–health relationships across the country.

Methods

Results

The descriptive analysis of the variables is presented in table 1. Of all the respondents, 66.19% reported good health, 22.73% reported fair health and 11.08% reported poor health. 62.13% of respondents were aged between 60 and 69, 96.5% of respondents were Han Chinese, 75.3% of individuals were not married, 63.8% of respondents were local agricultural hukou and about 90% of individuals with low education (junior high school or below). Only 25% had primary endowment insurance scheme, and about 40% had basic medical insurance scheme. About 50% of the respondents lived in rural areas. The average housing area per capita was 32.57 square metres. About 77% lived in houses constructed after 1978, and 45.64% in houses with less than two types of facilities.

Table 2 presents the results of the multilevel logistic regression. Model 1 includes covariates only. Older people who were female, at advanced age, not married, and less-educated were more likely to report fair or poor health than were their male, younger, married and more-educated counterparts. Local and agricultural hukou holders were more likely to report fair or poor health than were their non-local and non-agricultural counterparts. Primary endowment insurance recipients and urban residents were less likely to report fair or poor health than were non-recipients and rural residents. Moreover, older people who lived in larger, more recently constructed and better-equipped houses were less likely to report fair or poor health than those living in smaller, older and less-equipped houses.

The results of model 2 show that the level and rate of population concentration were negatively associated with the odds of reporting fair or poor health (OR 0.93, 95% CI 0.87 to 0.99 and 0.74, 95% CI 0.59 to 0.93, respectively), while the level of health services was positively correlated with the odds of reporting fair or poor health (OR 1.12, 95% CI 1.06 to 1.19). There was no significant relationship between the odds of reporting fair or poor health and the level of land-use conversion, economic growth (land-use conversion: OR 0.99, 95% CI 0.97 to 1.01; economic growth: OR 0.91, 95% CI 0.81 to 1.01). Similarly, no significant relationship was observed between the odds of reporting fair or poor health and land-use conversion rate, economic growth rate and health service improvement (land-use conversion rate: OR 0.96, 95% CI 0.90 to 1.02; economic growth rate: OR 0.94, 95% CI 0.85 to 1.05; health service improvement: OR 0.91, 95% CI 0.67 to 1.25).

The results of the moderating effect of education on the association between the level of urbanisation and SRH are shown in table 3. The level of land-use conversion was negatively associated with the SRH of the least educated (OR 0.98, 95% CI 0.96 to 1.00) and positively associated with the odds of those who had completed primary education reporting fair or poor health (OR 1.02, 95% CI 1.02 to 1.03; OR 1.04, 95% CI 1.03 to 1.05; and OR 1.03, 95% CI 1.02 to 1.05) (model 3). The level of economic growth was not significantly associated with the SRH of the least educated (OR 0.95, 95% CI 0.88 to 1.02) and was positively associated with that of other educational groups (OR 1.08, 95% CI 1.05 to 1.12; OR 1.19, 95% CI 1.11 to 1.26 and OR 1.14, 95% CI 1.05 to 1.24) (model 4). The level of population concentration was negatively correlated with the odds of reporting fair or poor health across all educational groups, and the strength of the negative relationship decreased with higher level of education (OR 0.84, 95% CI 0.79 to 0.89; OR 1.08, 95% CI 1.05 to 1.10; OR 1.19, 95% CI 1.13 to 1.26 and OR 1.19, 95% CI 1.11 to 1.28) (model 5). The level of health services was positively correlated with the odds of reporting fair or poor health across all educational groups with the strongest positive relationship found in senior high school (OR 1.05, 95% CI 1.01 to 1.09; OR 1.04, 95% CI 1.02 to 1.05; OR 1.07, 95% CI 1.04 to 1.10 and OR 1.04, 95% CI 1.00 to 1.07) (model 6).

Table 4 presents the results of the moderating effect of education in the association between the rate of urbanisation and SRH. The rate of land-use conversion was negatively correlated with the SRH of the least educated (OR 0.92, 95% CI 0.86 to 0.98) and not significantly associated with the odds of those who had completed primary education reporting fair or poor health (OR 1.01, 95% CI 0.99 to 1.04; OR 1.04, 95% CI 0.99 to 1.10 and OR 1.06, 95% CI 1.00 to 1.13) (model 7). Economic growth rate was negatively correlated with the odds of those who had education of junior high school or below reporting fair or poor health (OR 0.95, 95% CI 0.91 to 1.00) and not significantly correlated with other educational groups’ SRH (OR 1.00, 95% CI 0.90 to 1.12; OR 0.94, 95% CI 0.84 to 1.05 and OR 0.96, 95% CI 0.84 to 1.10) (model 8). The rate of population concentration was negatively associated with the odds of those without schooling reporting fair or poor health (OR 0.73, 95% CI 0.56 to 0.94) and not significantly associated with that of those who had completed primary education (OR 0.99, 95% CI 0.81 to 1.22; OR 1.48, 95% CI 0.97 to 2.24 and OR 0.89, 95% CI 0.52 to 1.51) (model 9). The rate of health service improvement was positively correlated with the SRH of the most educated (OR 1.88, 95% CI 1.21 to 2.94) (model 10).

Discussion

This study is the first study to examine the association between the multiple dimensions of urbanisation and SRH among older adults using nationally-representative survey data covering most of the prefectures in China. In contrast to previous studies examining urban health penalty in Chinese people across all ages,6–8 16 our findings show that living in more densely populated areas and areas undergoing rapid population concentration decreases older people’s odds of reporting fair or poor health. Fast-growing and densely populated cities draw numerous healthy and working-aged migrants from rural and small-town areas,35 36 and most of these migrants still perceive themselves to be healthy when they cross the age of 60 years (healthy migration phenomenon).19 On the other hand, as per traditional Chinese culture, people revert to their origin when they are old; migrants who perceive themselves to be unhealthy are likely to return to their rural and small-town hometowns when they retire or are close to retirement age (‘salmon bias’ phenomenon).30 Additionally, unhealthy older migrants would go back to their hometowns to avoid high healthcare expenditure in urban areas. The health selective migration partially accounts for the positive association between population concentration and SRH.

Earlier studies have attributed urban health penalty in China to changes in health behaviours associated with urbanisation.7 8 16 Specifically, people living in more urbanised areas are more likely to have unhealthy lifestyles, such as insufficient physical activity and high-fat and high-calorie intake.7 8 16 Nevertheless, our study found no evidence that economic growth and population concentration may have a detrimental effect on people’s SRH. This suggests that the pathway of lifestyle is less pronounced for older people than for the working-age population in China, as many older people living in well developed and densely populated areas still maintain their existing healthy lifestyle (ie, more physical activities and less high-fat and high-calorie intake) that was established many years ago (when China was a less developed and isolated country). Another pathway of urban health penalty involves environmental pollution and decrease in cultivated land.2 8 12 However, our results show no relationship between land-use conversion and economic growth on the one hand and older people’s SRH on the other, which suggests that environmental pollution and decrease in cultivated land might play little role in the association between urbanisation and older people’s SRH.

Urbanisation may also positively affect people’s health through improved healthcare services and quality of life.5 These pathways are associated with two dimensions of urbanisation, economic growth and health service improvements, which are found to be either non-significantly or counterintuitively positively related to older people’s odds of reporting fair or poor health. Economic growth was not accompanied by an increase in older people’s odds of reporting fair or poor health, probably because health benefits as a result of economic growth might be offset by associated detrimental effects such as environmental deterioration, increased stress and weakened social bonds. Surprisingly, the level of health services was positively associated with the odds of older people reporting fair or poor health, and health service improvement was not linked to an increase in older people’s odds of reporting fair or poor health. One possible explanation for this finding is that older people living in areas with better health services are more likely to receive health knowledge and be aware of their trivial illnesses, and thus, may report themselves as unhealthy.

Education had a moderating effect on the association between each of the four dimensions of urbanisation and older people’s SRH. Land-use conversion was negatively associated with the odds of the least educated individuals reporting fair or poor health. One explanation is that older people without education are indigenous peasants living in their home villages. Those living in areas with a high proportion of urban land and areas that undergo rapid land-use conversion usually have a better economic well-being and quality of life than do their less-urbanised counterparts, and thus report a better health status. The effects of land-use conversion and economic growth on older people’s SRH are more detrimental to those who are more educated, probably because health behaviours differ greatly between those who are more educated and those who are less educated in economically developed areas.7 37 People with a higher level of education are more likely to consume more food than needed and adopt a new lifestyle than do less-educated people. Moreover, high-fat and high-calorie diets and sedentary behaviour are more prevalent in economically developed areas. By contrast, the educational gap in health behaviours is less pronounced in less-developed areas, as educated people in these areas do not have an unhealthy diet and sedentary behaviour.7 The negative effect of population concentration on older people’s likelihood of reporting fair or poor health was stronger for the less educated than for the more educated, probably because in the Chinese context, the effect of health-selective migration is stronger for less-educated people who are often manual labourers and whose employment opportunities rely on their physical health conditions. The relationship between the level of health service and fair or poor SRH was positive; the rate of health service improvement was positively correlated with fair or poor SRH for the most educated individuals. This suggests that they tend to have stronger health awareness and higher expectations regarding their health when already living in areas with a high level of health services.

This study has some limitations. First, we were unable to capture the causal effect of changes in urbanisation over time on older people’s health outcomes due to the cross-sectional nature of the data. Second, our estimates of the effect of urbanisation on health might be subject to self-selection bias, as older people with certain observed or unobserved characteristics (eg, having well-educated parents) are more likely to live in more urbanised areas and report better health than are those who do not have those characteristics. Given that the middle-aged and older people in China have a low migration rate, we can assume that self-selection bias is not a severe issue for the present study. Third, we did not explore the pathways (eg, health behaviours, the use of healthcare facilities and services, and social capital) through which urbanisation affects SRH due to the lack of relevant information in our dataset.

In conclusion, the results show that the odd of older people reporting fair or poor health is negatively correlated with the level and rate of population concentration and is positively correlated with the level of health services. These findings support the healthy migration and ‘salmon bias’ hypotheses. Education had a moderating effect on the association between each of the four dimensions of urbanisation and older people’s SRH. The possible explanations for the difference between more educated and less educated older people in terms of urbanisation–health relationships include health-selective migration, differing quality of life, differing health behaviours and varying health expectations. Public efforts such as the equitable distribution of health services and the elimination of social exclusion of migrants should be made to decrease health inequalities among older people in China.