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Introduction

If a young male in East Asia is tall in height, above 180 cm, one or both his parents is likely to be tall. It’s genetics. In Europe, people in the northern regions, Sweden and the Netherlands, are conspicuously taller than those in the southern regions, Italy and Portugal, for example. It is also genetics, or so the author presumed, until recently.

Figure 1 displays changes of mean height of young men at age 20 in the Netherlands, France and Portugal from 1860 to 2000 [2]. Young men in the Netherlands were 183-4 cm, 7-8 and 10 cm, respectively, taller in mean height than in France and Portugal in the end of the 20^th century. In the mid-19^th century, young men in the Netherlands, were 165 cm, barely 1.0 cm and 2.0 cm taller, respectively than in Portugal and France. Men in France overtook men in Portugal in the turn of the century and were 2.5 cm taller in the end of the last century, as mentioned above. Genetics alone is powerless in explaining the secular changes in men’s height in the past one and a half centuries in Western Europe.

Economies in North East Asia achieved very rapid progress after the end of WW II. Young men, accordingly, increased in height at unprecedently high speed. Children in Japan ceased to grow any taller in the mid-1990s, whereas Korean children kept growing in height afterwards to exceed their Japanese peers in mean height by 3-4 cm in the mid-2000s and they ceased to grow any taller (Table 1). The “bubble” burst in the early-1990s in Japan’s economy but Korean economy kept growing very vigorously in the 2000s to match Japan in respect of per capita GDP in the end of the 2010s (IMF database) [3]. Supply(=consumption) of animal sourced-foods kept increasing in the 1980s and 1990s in Japan and consumption of animal protein continued to increase in South Korea until the end of the 2010s. Did the two countries attain their respective “genetic potentials” in height, with Koreans commanding a 3.0 cm advantage over their Japanese peers?

Comparisons in Growth Velocity

Data

Japan and South Korea have conducted national nutrition surveys, in which mean the height of subjects from 1 to 25 years old, and 26-29, 30-39, so on by age are published. However, the size of survey samples in Japan is not very large, 46 boys for the age group, 17 years old in 2000, for example, with mean height=170.9 cm, and SD=6.4[4]. School Health Examination Surveys have been conducted in the two countries for years, with nationwide samples, with some data limitations, with preschool children under 5 years of age and college students, above 18 years of age not covered [5;6]. Accordingly, this article will analyze changes in mean height of 1^st graders in primary school, 6 years of age through seniors in high school, 17 years of age.

Growth Curves or Velocity

Children born in 2017, for example, grew to 1 year old on their birthdays in 2018 and it will be the year 2034 when they will reach age 17 years. No one grows from 1 year old to 17 years old instantly in the same year. The year 2000 birth cohort, grew to 1^st graders, 6 years of age in 2006, 1^st graders in middle school, 12 years of age in 2012 and seniors in high school, 17 years of age in 2017, the end year in this analysis. Similarly, children 6 years-old, in 2000, the 1994 birth cohort, grew to middle school 1^st graders in 2006 and reached their last school years as, seniors in high school in 2011. No one grows instantly from 1^st graders in primary school to seniors in high school in the same survey year, say in 2000 or 2011.

Figure 2 displays changes in growth velocity of school boys in Japan and Korea, from 1^st grade in primary school, 6 years old to senior grade in high school, 17 years old, for the period from 2000 to 2017. Upper left in the graph, 55.3 cm for Korean boys, measures the differences in the mean height of senior high school boys in 2000, 172.9 cm from primary school 1^st graders in 1989, 117.6 cm. At the lower end of the same graph, 52.7 cm represents the difference between senior high school boys and 1^st graders in primary school in 2000, 120.2 cm, which is by no means actual, or longitudinal growth at all.

High school seniors in Korea in the beginning of the 2000s have grown 1.1 cm faster than their Japanese peers but they began to grow appreciably slower than their Japanese peers and Korean boys have grown nearly 2 cm, less or slower in velocity than their Japanese peers in the end of the survey period, 2017. This raises the questions: why has growth velocity declined steadily among Korean school boys since the early 2000s, whereas their Japanese peers have kept almost constant in growth velocity, growing appreciably faster than their Korea peers toward the end of the 2010s? South Korea’s economy kept rapid prosperity since the early 1990s, when the “bubble burst” in Japan’s economy and people’s food consumption improved only modestly.

A few years ago, when the author began to be involved in the comparative analyses of child height development, he surmised that Korean children tended to grow appreciably faster than their Japanese peers in their adolescent years, say after 12-13 years of age, likely because of their ethnic traits, although data were very limited. To verify his initial impression, Fig. 3 was prepared, showing height growth velocity from 1^st graders in middle school, 12 years of age to high school seniors, over the slightly expanded period from 1995 to 2017.

As the author presumed, Korean boys grew much faster than their Japanese pears in velocity in adolescence, from middle school 1^st graders to high school seniors in the 1990s through the early 2000s but they kept declining persistently in growth velocity to 2012, nearly 3 cm slower than their Japanese peers (Figure 3). The same question is raised here again: what factors may have caused these changes?

Height as a Net Measure of Inputs to Health

Per capita supply of animal products kept increasing steadily in the 2000s and 2010s in South Korea (Table 2) [7]. Per capita supply of vegetables kept remaining at high level after the turn of the century (Table 3) [8, 9]. It was discovered by the author, however that children in South Korea started to turn away from vegetables in the mid-1990s at their household food consumption, including boxed-lunch brought to school before nation-wide school lunch programs launched in the early-2000s. Children in growing ages, 0-9 and 10-19 began to reduce their at-home consumption of vegetables drastically, along with their rice consumption at home, including boxed-lunch. In the end of 2010s, children in Korea are estimated to consume only 10% of vegetables as compared to the older cohorts in their 50s, although per capita national consumption of vegetables kept quite high in the international context.

Household Income and Expenditure Surveys, Statistics Korea [10], provide household expenditures (in won) on major food items, grains, meats, fruit, vegetables, etc. classified by age groups of household head (HH). The author derived per capita household expenditures on vegetables, grains (≒polished rice) and meats (processed meats included) by individual members of household by age groups, 0-9, 10-14, 15-19, 20-29, --, by means of the TMI model [11], every year from 1990 to 2019. The estimates of per capita expenditures on vegetables, rice and meats, by 2 year-averages, from 1990-91 to 2017-19 are provided in Table 5, in terms of percentage of the control age group in their 50s every year.

Traditionally, bowls of rice with lots of kimchi [12-16], plus some meat/fish typify Korean dishes. As more meats/fish added, children grew taller in height, as shown in Table 1. Children seem not grow taller in height, or tend to decline in height, however, if consumption of kimchi is reduced appreciably in accordance with greater meat intakes. The author was told by native Korean colleagues that some burger-chains launched “kimchi-burgers” some time ago, with no success.

Conclusions

“A high consumption of animal protein does not result in increasing body height, if overall consumption of calories and other nutrients is insufficient” [1] (Blum, 2013). The author has been arguing that children in Japan began to slow-down in body height growth in the 1980s, when the national economy prospered and they ceased to grow taller at any age in the early-1990s, when consumption of animal products was still on the steady increase but per capita consumption of fruit had been radically reduced among children and younger generations [17,18].

Per capita fruit consumption among Korean children was plentiful but consumption of vegetables started to decline steadily in the mid-1990s and the Korean children consumed only one-tenth of vegetables as the older adults in their 50s in the mid-2010s. Consumption of ‘essential nutrients’ was apparently insufficient among the Korean children and pregnant mothers in their 20s and 30s (Table 5). Cole and Mori concluded a few years ago that most of the height increment seen in adults had already accrued by age 1.5 years of age [19].

It is possible that the reduced fruit consumption by young Japanese and the reduced vegetable consumption by young Koreans influenced the extent and timing of the declines in height growth velocity that are documented here. Further research on these possible associations is encouraged.

Acknowledgements

The author is grateful to Dr. Howard Elliott, former Deputy Director General, ISNAR, The Hague, for advices on discussions and usage of technical language. The author is also grateful to Mr. John Dyck, formerly an economist at ERS, USDA, for his thorough English editing.