Bulletin of the World Health Organization

Physical growth of children and adolescents in China over the past 35 years

Xin-Nan Zong a & Hui Li a

a. Department of Growth and Development, Capital Institute of Pediatrics, No. 2 Yabao Road, Chaoyang District, Beijing 100020, China.

Correspondence to Hui Li (email: huiligrowth@163.com).

(Submitted: 18 June 2013 – Revised version received: 10 December 2013 – Accepted: 14 January 2014 – Published online: 05 June 2014.)

Bulletin of the World Health Organization 2014;92:555-564. doi: http://dx.doi.org/10.2471/BLT.13.126243

Introduction

In 1978, the Government of China introduced economic reforms to convert the country’s planned economy into a free-market system. Since then, sustained economic productivity has greatly increased the food supply, average household income and personal expenditure on food.1,2 With increasing urbanization, the average Chinese diet has become higher in fat and calories, and lower in dietary fibre.3 Also, the level of physical activity during work and leisure time has declined.4 In short, dietary changes after these economic reforms have been accompanied by a rise in diseases related to affluence.5,6

Child-growth assessments are useful not only for monitoring a population’s nutritional status, but also for gauging inequalities in human development among different populations.7 Although many growth and nutrition surveys among children and adolescents have been carried out in China,8,9 few have tried to link trends in child growth and nutrition to changes in economic development. One study that evaluated the effects of China’s economic reforms on the growth of children showed an increase in the average height of children in both rural and urban areas. However, the increase in urban areas was five times that of rural areas.10

Since the economic reforms, income inequalities have increased between western rural areas and coastal areas, as well as between and within rural and urban areas.11 These inequalities have probably influenced the regional distribution of malnutrition and how this distribution has changed over time.12

The objective of this paper is to give an overall picture of long-term trends in the growth and nutritional status of Chinese children and adolescents by examining the results of seven large surveys conducted over the past 35 years. We focused on regional disparities in child and adolescent growth and nutritional status, as well as on changes in the pattern and rates of malnutrition after the transition to a more high-fat, high-energy-density and low-fibre diet in an attempt to determine if these changes were associated with the country’s economic development.

Methods

Data procurement

Growth and nutrition data

Data on the growth and nutritional status of children and adolescents between 0 and 18 years of age were extracted from published data and raw datasets of seven large surveys undertaken in one or more areas with different economic characteristics in China between 1975 and 2010. The following surveys were included: National Growth Survey of Children under 7 years in the Nine Cities of China; National Growth Survey for Rural Children under 7 years in the Ten Provinces of China; National Epidemiological Survey on Simple Obesity in Childhood; Chinese National Survey on Students’ Constitution and Health; China National Nutrition Survey; Chinese Food and Nutrition Surveillance system and China Health and Nutrition Survey. A summary of these surveys can be found in Table 1.

Classification of economic areas was based on five indices: regional gross domestic product (GDP), total yearly income per capita, average food consumption per capita, natural growth rate of population, and the regional social welfare index.8 The areas were categorized from highest to lowest economic status as large coastal cities, high, medium or low cities, high, medium or low rural areas and poor western rural areas.

Economic data

Development indicators for China were obtained from the World Bank;29 GDP per capita, the Gini index and the percentage of the population living in urban areas between 1970 and 2012.

Mortality data

Mortality rates for infants and for children less than 5 years of age between 1990 and 2013 were obtained from the Global Burden of Disease study.30

Dietary data

Dietary data for children and adolescents – daily intake of calories, fats, and protein – were obtained from the China Health and Nutrition Survey24 and the China National Nutrition Survey.20

Sedentary behaviour and physical activity

To describe trends in the level of physical activity, data on sedentary behaviour (hours per day watching television or videos or using the computer) and on passive commuting to and from school were obtained from replies to the China Health and Nutrition Survey questionnaire.25,26

Data analysis

Since the study designs, location and demographic characteristics of the population vary among the surveys, data from subsequent rounds of the same survey were used to assess trends. We assessed undernutrition using data for underweight and stunting. Underweight was defined as less than minus two standard deviations from the median weight-for-age of the reference population. Stunting was defined as less than minus two standard deviations from median height-for-age of the reference population. We assessed obesity using data for both overweight and obesity as defined by the Working Group on Obesity in China, adjusted for each year of age.31

We examined the statistical associations between physical growth and economic development using ecological comparisons and trends. To explore the relationship between height and GDP and urbanization and infant and child mortality rates, we calculated Pearson’s correlation coefficients (r), adjusting for sex. Trends in the prevalence of underweight, stunting, overweight and obesity were assessed using the χ2 test. SPSS version 13.0 (SPSS Inc., Chicago, United States of America) was used for the statistical analyses.

Results

Secular trends in growth

Between 1975 and 2010, the average height of children and adolescents increased steadily, without any tendency to plateau. The largest increment was noted around puberty, particularly among males, e.g. an increase of 11.9 cm in 13-year-old urban boys. The difference in height between the sexes at 18 years of age increased from 10.3 cm to 12.3 cm during this same period.

Body weight increased in both sexes and all age groups from 1985–2010. After 2005, in all age categories boys were heavier than girls (Fig. 1). To assess whether the increase in adolescents’ average height was associated with economic development – as captured by urbanization, GDP per capita and the Gini index – (Fig. 2), we looked for correlations between two of these indicators and the average height of adolescents 17–18 years of age.

Fig. 1. Changes in physical height and body weight of children and adolescents living in Chinese urban areas, 1975–2010
Fig. 1. Changes in physical height and body weight of children and adolescents living in Chinese urban areas, 1975–2010
Sample size: n = 140 229 aged 0–18 years in 1975; n = 79 194 for children less than 7 years of age in 1985; n = 79 154 for children less than 7 years of age in 1995; n = 69 760 for children less than 7 years of age in 2005; n = 204 973 aged 7–18 years in 1985; n = 105 409 aged 7–18 years in 1995; n = 117 997 aged 7–18 years in 2005 and n = 107 574 aged 7–18 years in 2010.
Data sources: National Growth Survey of Children under 7 years in the Nine Cities of China13 and Chinese National Survey on Students Constitution and Health.32
Fig. 2. Trends in gross domestic product (GDP) per capita, Gini index, urban population and child mortality rate in China, 1975–2010
Fig. 2. Trends in gross domestic product (GDP) per capita, Gini index, urban population and child mortality rate in China, 1975–2010
US$, United States dollars.
Data sources: GDP, Gini index and urban population from the World Bank;29 infant mortality and under-5 years mortality rates from the World population prospects: the 2010 revision.30

Height showed a close correlation with GDP per capita (r = 0.90, P < 0.0001) and with urbanization (r = 0.92, P < 0.0001). We also looked for a correlation between the decline in infant and under-5 mortality rates (Fig. 2) and average height and observed that they were both negatively correlated (r = −0.95; P < 0.0001), even after sex adjustment (r = −0.94; P < 0.0001).

Geographical disparities

Differences in height were observed in areas having different economic characteristics. Data from the National Growth Survey of Children under 7 years in Nine Cities of China and the National Growth Survey for Rural Children under 7 years in Ten Provinces of China showed that, on average, children of both sexes in rural areas were 2.1 cm (standard deviation, SD: 1.2) shorter than those in suburban areas and 3.6 cm (SD: 2.0) shorter than those in urban areas.

According to the Chinese National Survey on Students’ Constitution and Health, children and adolescents between 7 and 18 years of age who lived in a coastal city were taller, on average, than those living in other provincial capitals. They were also markedly taller, on average, than those living in medium-sized or small cities. Similar differences were observed among rural areas showing high, moderate and poor economic development (Fig. 3).

Fig. 3. Physical heighta in children and adolescents of different economic status groups, China, 2005
Fig. 3. Physical height<sup>a</sup> in children and adolescents of different economic status groups, China, 2005
a Height was measured as length for children less than 3 years of age.
Sample size: n = 69 760 urban children less than 7 years of age; n = 69 015 suburban children less than 7 years of age; n = 95 925 rural children less than 7 years of age; n = 81 438 urban children and adolescents aged 7–18 years; n = 111 584 rural children and adolescents aged 7–18 years.
Data sources: National Growth Survey of Children under 7 years in the Nine Cities of China,13 National Growth Survey for Rural Children under 7 years in the Ten Provinces of China9 and Chinese National Survey on Students Constitution and Health.17,18

Trends in malnutrition

The prevalence of undernutrition in children less than 5 years of age was highest in poor rural areas. Compared with the 1990s, the overall prevalence of undernutrition has declined sharply – by 74% for underweight and 70% for stunting. Significant downward trends in the prevalence of both underweight and stunting were observed for all areas (P < 0.001). However, in poor rural areas in 2010, the prevalence of underweight and stunting was still high, at 8.0% and 20.3%, respectively (Fig. 4).

Fig. 4. Trends in underweighta and stuntingb in children less than 5 years of age, China, 1990–2010
Fig. 4. Trends in underweight<sup>a</sup> and stunting<sup>b</sup> in children less than 5 years of age, China, 1990–2010
a Underweight was defined as below minus two standard deviations from median weight-for-age of the reference population.
b Stunting was defined as below minus two standard deviations from median height-for-age of the reference population.
Sample size: n = 3200 rural children and n = 1130 urban children in 1990; n = 2139 rural children and n = 765 urban children in 1995; n = 10 729 rural children and n = 5770 urban children in 2000; n = 10 501 rural children and n = 5535 urban children in 2005; n = 10 596 rural children and n = 4803 urban children in 2010.
Data source: Chinese Food and Nutrition Surveillance System.2123

In 2010, the combined prevalence of overweight and obesity was found to be highest among urban boys (23.2%), followed by rural boys (13.8%), urban girls (12.7%) and rural girls (8.6%). Significant increases were noted in the combined prevalence of overweight and obesity in all groups (P < 0.001) (Fig. 5). Between 1985 and 2010, the proportion of obese males increased faster than that of obese females. In urban areas, male obesity increased 0.34 percentage points per year, compared with 0.15 for female obesity. In rural areas, the increase was 0.18 percentage points per year for male obesity, compared with 0.10 for female obesity. The increase in obesity in urban areas between 1985 and 2000 was twice that of the increase in rural areas during the same time period. However, between 2005 and 2010, the annual increase in obesity in rural areas has outpaced that of urban areas (0.34 versus 0.30 percentage points in males and 0.17 versus 0.10 percentage points in females).

Fig. 5. Trends in overweight and obesitya in children and adolescents, 7–18 years of age, China, 1985–2010
Fig. 5. Trends in overweight and obesity<sup>a</sup> in children and adolescents, 7–18 years of age, China, 1985–2010
a Overweight and obesity were defined by using the references of the Working Group on Obesity in China. The cut-offs for overweight and obesity were adjusted for each sex–age group.31
Sample size: n = 409 946 in 1985; n = 204 997 in 1995; n = 216 786 in 2000, n = 234 421 in 2005 and n = 215 319 in 2010.
Data source: Chinese National Survey on Students Constitution and Health.16

Fig. 6 illustrates the burden of obesity in areas with different economic characteristics. Large coastal cities were the first to exhibit a rise in overweight and obesity and had the largest increase in prevalence – 32.6% (males) and 19.1% (females) in 2010. Similar increases followed in other areas: first in large, prosperous cities, followed by medium-sized cities with a large middle class and, finally, by the more affluent rural areas. Although an increase in obesity was noted between 1985 and 2010 in western rural areas with low economic development, these areas still had the lowest prevalence of obesity in 2010.

Fig. 6. Changes in overweight and obesea children and adolescents, 7–18 years of age, in areas with different economic characteristicsb, China, 1985–2010

Trends in nutrition and physical activity

To assess whether factors associated with increased body weight in children and adolescents were affected by China’s economic reforms, we obtained data on fat and protein intake and level of physical activity. Between 1991 and 2009, people’s diets in China changed considerably. For children and adolescents between 7 and 17 years of age, the average daily fat intake increased from 55 to 66 g and the average daily protein intake decreased from 66 to 58 g. There was also an increase in fats as a proportion of total caloric intake and an increase in the proportion of children and adolescents obtaining more than 30% of their energy from fat. In addition, during this period time spent in front of a television, video or computer also increased, as did the proportion of children and adolescents who commuted to school in a motorized vehicle (Fig. 7).

Fig. 7. Changes in dietary intake (1991–2009)a and physical activities (1997–2006)b for children and adolescents, China
Fig. 7. Changes in dietary intake (1991–2009)<sup>a</sup> and physical activities (1997–2006)<sup>b</sup> for children and adolescents, China
a Dietary graphs include children and adolescents aged 7–17 years.
b Screen time includes watching television in 1997 and 2000, and watching television and using computers in 2004 and 2006. Passive commuting is the percentage of school-aged children who commuted to school in a bus.
Sample size: n = 2714 in 1991; n = 2542 in 1993; n = 2516 in 1997; n = 2142 in 2000; n = 341 in 2004; n = 1072 in 2006 and n = 996 in 2009.
Data source: China Health and Nutrition Survey.2426

Discussion

The economic transition

In the wake of the 1978 reforms, China underwent many changes in its social structures, living conditions and diet. This has been accompanied by a positive trend in the physical growth of children.33 An empirical division of China’s economic development into stages based on the time cycle of China growth surveys facilitates the analysis of its association with trends in children’s growth. In Stage I (before 1975) – out of scope of this analysis – a previous subtle upward trend in growth ceased and even reversed owing to the detrimental effects of famine. In Stage II (1975–1985), children’s growth began to improve again with the recovery of the national economy, and positive trends emerged in older age groups of children in the major cities. In Stage III (1985–1995), physical growth continued to improve in parallel with sustained economic growth. The increment in height among children in rural areas exceeded that seen in children living in urban areas because of improved living standards, health care and increased food supply in the rural areas in the mid-1980s.9 In Stage IV (1995–2005), even higher growth increments were documented among both urban and rural residents. According to data from 2005 to 2010 (Stage V), the increment has continued and does not seem to be levelling off.34

The growth of children in China has improved in recent decades and this improvement is more pronounced at puberty than at earlier or later ages, consistent with other population-based studies.35 The increase in height at the age of 18 years is already present in younger ages and the eventual increase in adult height is established during the first 2 years of life.

In the Netherlands, the secular increase in growth has come to a halt after 150 years, with males now 13.1 cm taller on average than females.36 Since sex difference in adult height widens gradually as secular increases in growth continue, the difference of 12.3 cm between the sexes in 2010 suggests that the positive trend in Chinese children may continue.

Before the economic reforms, food had been in short supply,3 but after 1978, when a policy of liberal food production was introduced and annual economic growth improved, people began to eat more meat and grains and less vegetables. Child growth and nutrition improved and overweight and obesity were still rare. In 1985 and 1986, the prevalence of obesity in children and adolescents was below 1% in large cities.15,19

In 1986, China started its first specific survey on obesity and found that the Chinese diet had become richer in fats and calories and lower in fibre, a change that was introducing an increased risk of chronic diseases.37,38 Obesity among infants and preschool children increased by a factor of 2.8 between 1986 and 2006.15 And between 1985 and 2010, overweight among school-aged children and adolescents increased from 1.11% to 9.62% and obesity from 0.13% to 4.95%.16 Additionally, between 1993 and 2009 the prevalence of obesity rose from 6.1% to 13.1% among children between the ages of 6 and 17 years.39 The higher prevalence of overweight males contrasts with the situation in some non-Asian countries.40

In 2012, for the first time in history, China’s urban population outnumbered its rural population.41 This urbanization can be seen as a double-edged sword. Although it has brought increased access to health care and improvements in basic health infrastructure for many, it has also brought about changes in diet and lifestyle, such as an increase in the availability of sweets and fast-food restaurants and in the use of television, personal computers and cars, all of which can pose substantial health risks.42,43

We have shown that in recent decades fat intake and physical inactivity have risen among Chinese children, with a resulting increase in childhood obesity and a documented decline in physical fitness. For instance, the capacity for endurance running among Chinese students declined significantly between 1985 and 2010.32,44

Dual burden of malnutrition

Large discrepancies still exist between rural and urban areas both in health conditions and in health care.45 Decades of observation suggest that despite improved growth in children belonging to all economic groups, a large growth disparity persists between the rural and suburban areas and the urban areas,9 and among different economic subgroups within these areas.17,18

Compared with the late 1980s and early 1990s,46 in 2010, malnutrition in childhood declined dramatically, owing to sustained economic development, sound nutrition policies, improved health services for women and children and broad implementation of child nutritional interventions.23 However, in the same year, nutrition in rural areas was still poor, with a high prevalence of underweight and stunting among children less than5 years of age. Another survey in 2009 reported 15.9% prevalence for stunting, 7.8% for underweight and 3.7% for wasting in poor rural ares.47

We have also observed a paradoxical situation: in 2006, prevalence of overweight children was as high as 16.8%, while that of stunting was 57.6% among the children in the same poor areas of China’s midwestern provinces.48 The coexistence of stunting and overweight in the same child is a result of protein and energy malnutrition, which retards height despite increased body weight,49 and Chinese rural children have a lower daily protein intake than urban children.24

Childhood obesity has become a serious public health problem in China.19,50 The current strategies for preventing and controlling malnutrition need to be re-examined. Research on obesity prevention and control needs to be improved and nutrition policies need to be aligned with appropriate obesity prevention strategies. Cross-sectoral collaboration such as between health and agriculture, needs to be promoted.

Our study has shown that regional inequalities in child growth and nutrition in China accompany regional economic disparities. Therefore, to promote equitable growth for all children in China, strategies for optimal nutrition need to focus more closely on disadvantaged groups in the poor and underdeveloped areas.


Funding:

National Natural Science Foundation of China (No.81302439).

Competing interests:

None declared.

References

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