Index Introduction Subjects and Methods Results Discussion References

Introduction

Secular growth changes, which were one of the great 19th century discoveries in human growth, were prominent in the 20th century, especially after World War II. This phenomenon has been well documented in many developed and developing countries (Eveleth and Tanner, 1990). In the long term, a secular trend is a product of a continuous and often non-additive interaction between genetic and environmental forces. However, the short term ranges involved (a few generations or a single generation) indicate that secular trends are likely to result not from alterations in the genetic constitution of populations, but in the environment in which growth takes place (Castilho and Lahr, 2001). In the 1980s onwards, some studies reported that the acceleration of physical development had already ceased or reached a plateau in some developed countries, which suggests that they were possibly about to achieve their full genetic potential or that their socioeconomic conditions had ceased to improve (Lindgren, 1998; Lintsi and Kaarma, 2003; Krawczynski et al., 2003).

The most important environmental factors to influence secular growth changes are nutrition and health. Socioeconomic living conditions, control of infectious diseases through mass immunization, social and health care (preventive and curative), sanitary conditions, minimum income, level of education, industrialization, and urbanization, as well as psychological state, appear also to be significant factors contributing to secular trends by removing factors that had blocked full expression of biological potential (Van Wieringen, 1986; Malina et al., 1987; Tanner, 1992; Hauspie et al., 1996; Bodzsar and Susanne, 1998; Castilho and Lahr, 2001; Whitehead, 2003).

In fact, during the second half of the 18th century until the mid and late 19th century, a straightforward association between economic growth and improvement in living standards did not necessarily occur. The reason may be deduced from the fact that industrialization did not directly bring increases in real wages and better standards of living to people because of the occurrence of Malthusian crises during episodes of rapid market expansion which led to a generalized decrease in nutritional status in spite of increased in per capita income (Ward and Ward, 1984; Komlos, 1985, 1993; Sandberg and Steckel, 1987). Not until the 20th century, especially after World War II, have positive secular trends in physical growth been shown to accompany economic status (Matsumoto, 1982; Lopez, 1995; Padez, 2003; Krawczynski et al., 2003; Huang et al., 2003). In China, positive secular growth changes have been reported in anumber of respects. Shandong Province, located in the lower reaches of the Yellow River between 34°25′ and 38°23′ N latitude, and 114°25′ and 112°43′ E longitude, is an important littoral province in East China (Figure 1). Shandong Province is one of the birthplaces of Chinese culture and is the hometown of Confucius, widely considered to be the greatest philosopher in Chinese history. In particular, since China adopted the policy of reform and opening up to the world, Shandong has maintained sustained and rapid economic growth and is one of the most economically developed provinces in China (http://www.stats.com.cn/tjsj/tjsj.asp). The aim of the present study is to report secular trends in stature, body weight and body proportion of children and adolescents aged 7–18 years from Shandong Province over the period 1985–2005.

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Figure 1. The location of Shandong Province in China.

Subjects and Methods

The data derived from two national surveys on students’ constitution and health carried out by the government in 1985 and 2005 in Shandong Province, China. (In 1985, the government education and health department set up a system of National Surveys on Chinese Students’ constitution and health. The first author is a member of the leading group in Shandong Province). The sampling method was stratified multistage sampling based on economic status, drawn from Jinan (the capital and the political, economic, and cultural center of Shandong Province: this city has an area of 8227 square km, and a population of 6.43 million in 2005), Yantai (an eastern coastal and developed city, with and area of 13739 square km, and a population of 6.94 million in 2005; people’s living standards and seafood intake were relatively higher) and Jining (an inland developing city, with an area of 11000 square km, and a population of 7.82 million in 2005; people’s living standards were relatively lower) as survey areas (Figure 2), using randomly selected primary and secondary schools. The sample proportions in these three areas in each survey were equal. All of the subjects were primary and secondary school, covering the range from 7 to 18 years of age, and all of them were of Han ancestry, which accounts for approximately 99.32% of the total population in Shandong. All subjects had a thorough medical examination before the measurements were taken. They were all in apparently good health, and free from overt diseases or deformities. Most importantly, the schools from which the subjects were selected were relatively fixed since 1985, and the method and quality control of measurements of two surveys was the same (Research Section of the Constitution and Health of Chinese Students, 2007). From 1985 to 2005, the apparatus recommended by Cameron (1978) was used by doctors to measure height, weight, bicristal breadth, and biacromial breadth; the subjects were required to go barefoot and wore only their underwear. The age groups were divided following criteria of ‘exact age’, so that, for example, cohort 10- (represented by ‘10’ in the plots) designates students aged 10.0–10.9 years. The sample size of the age groups of each survey is given in Table 1.

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Figure 2. The location of the three cities studied in Shandong Province, China.

Cross-sectional height, weight, BMI, relative sitting height and acromiocristal index curves were created for both sexes. t-tests were utilized to analyze differences between every target of the 1985 and 2005 samples. Data concerning demography, socioeconomic status, and housing conditions were obtained from the statistical yearbook released in the official website of Shandong Provincial Statistics Bureau (http://www.stats.com.cn/tjsj/tjsj.asp). The main indicators included: total population, birth rate, natural increase rate, GDP per capita, income per capita, and housing area per capita.

Statistical tests were performed using the statistical package SPSS 11.0.

Results

Table 1 shows the means and SD of stature, body weight, sitting height, bicristal breadth, and biacromial breadth for subjects aged 7–18 in 1985 and 2005. t-tests indicate that the average height, body weight, sitting height and biacromial breadth for both boys and girls surveyed in 2005 were significantly higher than the 1985 values for all cohorts from 7 to 18 years (P < 0.01). The average bicristal breadths in 2005 were significantly higher than the 1985 values except for boys age 16 and girls aged 13–18. Figure 3, Figure 4, Figure 5, and Figure 6 show the positive secular trends in height and body weight from 1985 to 2005. In 7-year-old boys, height increased from 121.93 to 128.17 cm, and weight from 22.11 to 26.76 kg, a rate of 3.12 cm and 2.33 kg per decade. The girls increased from 120.75 to 125.87 cm and 21.16 to 24.54 kg, corresponding to a positive trend of 2.56 cm and 1.69 kg per decade. In 18-year-old boys, height increased from 169.56 to 174.23 cm, and weight from 58.81 to 65.82 kg, a rate of 2.34 cm and 3.51 kg per decade. The girls increased from 158.29 to 161.55 cm and 51.21 to 54.90 kg corresponding to a positive trend of 1.63 cm and 1.85 kg per decade. The biggest increments in height and weight were found in 13-year-old boys (from 154.27 to 163.07 cm and 41.84 to 54.69 kg), a rate of 4.40 cm and 6.43 kg per decade, and 12-year-old girls (from 147.69 to 154.90 cm and 36.80 to 44.83 kg), a rate of 3.61 cm and 4.02 kg per decade. These changes might represent the peak growth periods of adolescents.

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Figure 3. Curve of average stature for boys, 1985–2005.

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Figure 4. Curve of average stature for girls, 1985–2005.

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Figure 5. Curve of average weight for boys, 1985–2005.

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Figure 6. Curve of average weight for girls, 1985–2005.

Table 2 shows the means and SD of relative sitting height, acromiocristal index and BMI for subjects aged 7–18 in 1985 and 2005. Figure 7 and Figure 8 show the positive secular trends in BMI from 1985 to 2005. t-tests indicate that the average BMIs for both boys and girls surveyed in 2005 were significantly above the values of 1985 for all cohorts from 7 to 18 years (P < 0.01 or 0.05). In 7-year-old children, BMI increased from 14.83 to 16.17 kg/m² (boys), and from 14.48 to 15.39 kg/m² (girls). In 18-year-olds, BMI increased from 20.43 to 21.65 kg/m² (boys), and from 20.43 to 21.03 kg/m² (girls). In the 20-year study period, BMI increased rapidly: the average increments of BMI for all the subjects were 2.13 kg/m² (boys) and 1.20 kg/m² (girls).

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Figure 7. Curve of average BMI for boys, 1985–2005.

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Figure 8. Curve of average BMI for girls, 1985–2005.

Relative sitting height reflects body proportion (ratio between trunk and legs); it decreases with age before puberty and increases with age after puberty (Figure 9, Figure 10). The mean values of boys and girls surveyed in 2005 were below the 1985 values; t-tests indicate that the differences between the two surveys are significant (P < 0.01) except for boys aged 13–15 and girls aged 13. The results show clearly that the increment in leg length was larger than that in trunk length during the 20-year study peroid.

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Figure 9. Curve of average relative sitting height for boys, 1985–2005.

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Figure 10. Curve of average relative sitting height for girls, 1985–2005.

The acromiocristal index reflects body shape (ratio between bicristal breadth and biacromial breadth); the curves of mean values are different between boys and girls. In boys, the index decreases with age, to a broad-shouldered, sturdy form, and in girls, the indes increases with age, showing a form with chubby buttocks. t-tests indicate that the average acromiocristal indices recorded in 2005 are significantly below the 1985 values except for boys aged 8–10. The results show clearly that the increment of biacromial breadth is bigger than bicristal breadth during the 20-year study periods (Figure 11, Figure 12).

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Figure 11. Curve of average acromio-cristal index for boys, 1985–2005.

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Figure 12. Curve of average acromio-cristal index for girls, 1985–2005.

Discussion

Secular changes were prominent in the 20th century (especially after World War II) and were expressed as a steady increase in mean height and weight of European and US populations (Van Wieringen, 1986). Concomitantly, assessments of the age at menarche have revealed progressively earlier ages of puberty onset in adolescents, largely related to improved health, general nutrition, and fat content in diet (Eveleth and Tanner, 1990). Positive secular trends in body dimension and growth rate are apparent worldwide in both genders during the last century, regardless of country, climate, ethnic group, or socioeconomic situation (Vlastovsky, 1966; Brundtland et al., 1975; Vercauteren and Susanne, 1985; Ji et al., 1995; Loesch et al., 2000; Padez, 2003). However, the extent of the changes varies during different periods, and some reports have even concluded that the tendency for the height of children to increase stopped or had come near to stopping in some European countries in the 1980s (Bodzsar and Susanne, 1998; Krawczynski et al., 2003).

This study on secular trends of physical growth in Shandong, China has shown that positive increments in height and weight occurred in boys and girls aged 7–18 years during the 20-year period from 1985 to 2005. The total increases of height and weight for the 8-year-old groups from 1985 to 2005 were 6.35 cm, 6.18 kg for boys and 6.14 cm, 4.62 kg for girls, which yielded rates of 3.18 cm, 3.09 kg and 3.07 cm, 2.31 kg per decade, respectively. The overall increases in height and weight for the 18-year-old groups during the 20-year study were 4.67 cm, 7.01 kg for boys and 3.26 cm, 3.69 kg for girls, which yielded rates of 2.34 cm, 3.51 kg for boys and 1.63 cm, 1.85 kg per decade respectively. These increments were higher than those of Brazilians (Castilho and Lahr, 2001). Ji et al. (2007) reported secular trends in Chinese urban children and adolescents aged 7–18 from 1979 to 2005; the average increments were 6.5 and 4.7 cm (2.5 and 1.8 cm/decade) for stature, and 8.9 and 5.2 kg (3.4 and 2.0 kg/decade) for weight, for boys and girls, respectively. The present article reports that the average increments of stature and weight for children and adolescents aged 7–18 from 1985 to 2005 in Shandong, China were 3.5, 2.7 cm/decade and 4.5, 2.7 kg/decade, for boys and girls, respectively, higher than those of China as a whole. This article also finds that a change in relative sitting height and acromiocristal index occurred over the 20-year study period, which we propose is probably related to the decrease in the amount of physical labour and needs further research.

Secular growth change is a complex biological phenomenon resulting from genetic and many environmental factors. It is generally considered to relate to economic development and improvement in social and health indicators (Robert and Anthony, 1979; Thomas et al., 1995; Loesch et al., 2000; Ayatollahi et al., 2006). Socioeconomic factors cannot influence physical growth directly, but act through biological factors such as nutrition (quantity and quality of food), infectious diseases, and access to health care and safe water. Some authors, such as Bogin (1998), considered that milk is an important component that influences positively the growth of children. Takahashi (1984) has linked the secular trend in height in Japan to the consumption of milk, which has risen steeply since World War II and concluded that milk consumption among the younger generation was one of the most important causes of the acceleration of growth in height. In Japan, there were similar increasing trends between children’s stature and the consumption of milk and eggs from the 1950s to 1960s (Ye, 1999). In Portugal, in addition to the increase in milk consumption, sugar consumption is another important element: the increase in sugar consumption has implications for the secular trend too because refined sugars provide more rapidly accessible energy (Ziegler, 1967). One of the present authors had previously collected the data of youngsters’ stature, body weight and the gross industrial output value per capita in 1956, 1962, 1972, 1979, 1985, and 1995 in Jinan, Shandong, China and reported the secular change of youngsters’ growth and its correlation with the development of social economics from 1956 to 1995. There were significant positive correlations among youngsters’ stature, body weight and the gross industrial output value per capita in different years (Zhang and Yu, 1997). Zhang et al. (2005a) also reported the secular growth change of children in Qingdao City, Shandong, China and its correlation with the development of socioeconomic status from 1962 to 2002. There were significant positive correlations among children’s stature and body weight and the main economic indicators (including GDP per capita, gross industrial output value per capita, total volume of retail sales of social consumer goods per capita, fishery output value index and annual income per capita) in different years (Zhang et al., 2005b). I had compared the secular growth change of children in Jinan and Qingdao Shandong, China from 1962 to 2000, the difference of children’s stature increases between the two cities were related to the difference of socioeconomic development (Zhang et al., 2005b).

Secular growth change is the result of a comprehensive effect involving many complicated factors, and cannot be explained by a single factor. These factors include genetic and environmental aspects: the possibility of growth is controlled by genetic factors and the reality by environmental factors. Improvements in environmental factors, including socioeconomic development, nutrition and living conditions, etc., provide conditions that allow genetic potential to be fully realized. The socioeconomic status of Shandong Province, including population size, economy, average income, and living conditions, improved rapidly from 1985 to 2005 (Table 3, http://www.stats.com.cn/tjsj/tjsj.asp), especially, the GDP per capita and income per capita in city and country, which increased by 21.7, 13.4, and 12.9 times, respectively. This provides suitable condition for positive secular growth trends in children and adolescents.

Secular growth trends are an important biological phenomenon. China is now experiencing a positive secular trend, which is reflected not only in faster growth in childhood, earlier puberty, and steady increments in adult height, but also by dramatic changes in body shape (Ji et al., 2007). This study has shown that the BMI of children and adolescents increased rapidly from 1985 to 2005; this trend might indicate that the prevalence of overweight and obesity increased rapidly, and overweight and obesity among adolescents has indeed become a serious public health problem. The recent increases in prevalence rates for both overweight and obesity in children merit particular attention. In the USA, rates of obesity increased from 5% to 10% between 1963 and 1990 amongst 6–11 year olds (Troiano et al., 1995). In a North American low-income population, the prevalence of overweight in preschool children based on the 85th cutoff point for weight-for-height increased from 18.6% in 1983 to 26.3% in 1995 (Mei et al., 1998). In China, the prevalence rates of obesity reported by CNSSCH in 1985 were only 0.2% and 0.1% for boys and girls, and the prevalence of overweight was between 1% and 2%, indicating no obesity epidemic at that time (Ji et al., 2004). However, a rapid increase in the prevalence of overweight has been noticed since the early 1990s. The prevalence rates of obesity plus overweight reported by CNSSCH had reached 25.4%, 25.5%, 17.0% and 14.3% in 2000 for boys aged 7–9 years and 10–12 years, and girls aged 7–9 years and 10–12 years, respectively (Ji et al., 2004).

In summary, these results reveal a sharp positive trend in growth in boys and girls aged 7–18 years during the 20-year period from 1985 to 2005 in Shandong Province, China. The major reasons for this change most likely relate to socioeconomic development and improvements in nutrition and living conditions.