Urbanization and the spread of diseases of affluence in China

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Abstract

We quantify, track and explain the distribution of overweight and of hypertension across Chinese provinces differentiated by their degree of urbanicity over the period 1991–2004. We construct an index of urbanicity from longitudinal data on community characteristics from the China Health and Nutrition Survey and compute, for the first time, a rank-based measure of inequality in disease risk factors by degree of urbanicity. Prevalence rates of overweight and hypertension almost doubled between 1991 and 2004 and these disease risk factors became less concentrated in more urbanized areas. Decomposition analysis reveals that one-half of the urbanicity-related inequality in overweight is directly attributable to community level characteristics, while for hypertension the contribution of such characteristics increased from 20% in 1991 to 62% in 2004. At the individual level, lower engagement in physical activity and farming explain more than half of the urban concentration of overweight and a rising share (28%) of the greater prevalence of hypertension in more urbanized areas. Higher incomes explain around one-tenth of the urban concentration of both overweight and hypertension, while the education advantage of urban populations has a similar sized offsetting effect.

Introduction

China is currently experiencing an urbanization process of remarkable scale. The percentage of the Chinese population living in urban areas increased from 27% in 1990 to 40% by 2005 (National Bureau of Statistics China, 2006; UN, 2007). By 2020, it is expected that this percentage will rise further to well over 50%, adding an additional 200 million mainly rural migrants to the current urban population of 560 million (UN, 2007, Yusuf and Saich, 2008). The consequences for population health are likely to be mixed. On the one hand, urban populations benefit from better access to health services, information and education, and have higher cash incomes and more economic opportunities (Liu et al., 1999, Moore et al., 2003). However, the rapid environmental, economic and social changes that follow urbanization increase the prevalence of major risk factors for chronic disease. In particular, urban areas in low and middle-income countries are moving through a rapid nutritional transition towards Western-style diets, dominated by more processed foods and a higher fat content (Popkin, 2003, Popkin and Du, 2003). Increasing urbanization also leads to equally rapid shifts toward more sedentary occupations through the acquisition of new technology and transitions away from a mostly agricultural economy (Monda et al., 2007a, Monda et al., 2007b). In China, these transitions have contributed to stark increases in the prevalence of conditions such as overweight and hypertension, especially amongst males, in urban areas and within high-income groups (Liu et al., 2004, Wang et al., 2005, Wang et al., 2007, Weng et al., 2007). The emergence of non-communicable diseases as a major health threat in countries still coping with infectious diseases and childhood malnutrition threatens to overstretch already struggling health services. Forecasts estimate that heart disease, stroke, and diabetes will cost China $556 in the period 2005–2015 (Wang et al., 2005).

Increasing urbanization and development is likely to drastically change the geographical distribution of these non-communicable diseases. This paper investigates how the prevalence of overweight and hypertension varies across areas of China at different stages of urbanization, and how and why this spatial distribution is changing over time. In order to target public health interventions appropriately, it is important to establish whether these disease risk factors are spreading to less urban areas, or whether they are merely rising in the most urban ones. Knowledge of whether the geographic distribution of so-called diseases of affluence is changing because of changing population characteristics, behaviors or environmental factors is essential in identifying the type of interventions that are most likely to be effective in halting the spread of these diseases.

Analysis based on an urban–rural dichotomy does not adequately distinguish the different living and health conditions experienced in areas at different stages of urbanization (McDade and Adair, 2001, Vlahov and Galea, 2002, Champion and Hugo, 2004, Dahly and Adair, 2007). Further, there is no universally agreed definition of “urban” and “rural”, and in China the classification may have been influenced by the privileges to which non-agricultural residents were entitled (Kojima, 1995, Heilig, 1999).1 New criteria for the designation of cities and towns were introduced in 1983, resulting in changes in the definition of urban administrative areas. These have necessitated changes in the census definition of the urban population from time to time, causing much confusion in counting the number of urban Chinese dwellers (Wu, 1994, Shen, 2006). Analysis of longitudinal survey data often presents a further problem in that the categorization of an area as urban or rural is fixed over survey waves. This is the case in the China Nutrition and Health Survey (CHNS) used here and so the dichotomous urban–rural variable does not capture the rapid urbanization of many designated rural areas that has occurred over the survey period.

To overcome these problems, we construct an urbanicity index using community data from the CHNS.2 This index gives a ranking of communities from low to high levels of urbanicity, facilitating, for the first time in the urbanization literature, the use of rank-based measures of spatial inequality in overweight and in hypertension across areas at different stages of urbanization. We also use a decomposition method to explain what is driving these urbanicity-related inequalities in overweight and hypertension, and their trends over time. This method identifies the contribution of each determinant to inequality in the distribution of the disease risk factor by urbanicity, and makes clear that this contribution depends both on the urban concentration of the determinant and on the strength of its correlation with the risk factor. Changes can occur because the factors that determine overweight/hypertension are becoming more/less concentrated in urban areas over time, or, for a given geographical distribution of the determinants, because their impact on overweight/hypertension is strengthening/weakening.

Section snippets

Data

This study uses data from the CHNS (http://www.cpc.unc.edu/projects/china), a large scale (and ongoing) longitudinal survey conducted in nine provinces of China in 1991, 1993, 1997, 2000 and 2004.3 The provinces represented in the survey are Liaoning, Shandong, Jiangsu, Henan, Heilongjiang, Hubei, Hunan, Guangxi and Guizhou (Fig. 1). We have not included Heilongjiang in our analysis as

Index construction

The concept of an urbanicity index was introduced by Allen (1976), and since then there have been attempts to develop an index from community level survey data. McDade and Adair (2001) use factor analysis on data from the Philippines, while Dahly and Adair (2007) assign weights to various community variables from the same data. For China, Liu et al. (2003) create an index by weighting various community characteristics. Recently, Ng et al. (2009) explored the different dimensions of urbanization

Measurement

Following Wagstaff et al. (1991), the concentration curve and index have been popular tools for assessing socioeconomic inequalities in health. Given these are rank-based measures of inequality, they can also be used to assess urbanicity-related inequality with ranking provided by the urbanicity index. We use this approach to measure the degree to which overweight and hypertension are disproportionately concentrated among individuals located in more urbanized areas.

A concentration curve plots

Results

In this section, we first document the extent to which overweight and hypertension are concentrated among more urbanized areas and how this concentration has changed from 1991 to 2004. We then explain the urbanicity-related inequality in the two disease risk factors in relation to the distribution and impact of their determinants. By comparing how the contributions of these determinants have changed from 1991 to 2004, we identify which factors are driving changing urbanicity-related

Discussion

This paper has quantified, tracked and explained the distribution of two important risk factors for chronic diseases – overweight and hypertension – across Chinese communities at various stages of the urbanization process over the period 1991–2004. Both in 1991 and in 2004, overweight and hypertension were more prevalent in the more urbanized areas. However, while the prevalence rates of these conditions have almost doubled over the period 1991–2004, inequalities across areas at different

Acknowledgments

The authors wish to thank five referees and John Komlos (editor) for valuable comments on previous versions of this paper. The data were supplied by the China Health and Nutrition Survey, funded by NIH (R01-HD30880, DK056350, and R01-HD38700) and the Carolina Population Center and the Chinese CD. We thank Alex Fu, Gordon Liu, Lars Osberg and Kuan Xu for information on data issues. Funding from the Institute for Housing and Urban Development Studies, Erasmus University Rotterdam under the

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