Comparative Analyses of Height Growth Velocities of School Boys in South Korea and Japan in the Past 50 Years

The paper compares the height growth velocities of male schoolchildren in South Korea and Japan over the period 1961-2018. Growth in height was measured with the same birth cohorts, not by comparing mean height of as-cending ages in the same year. Starting from a lower economic base and mean height in the 1960s, high school males aged 17 in South Korea became 3 cm taller in mean height than their Japanese peers in the mid-2000s versus 2 - 3 cm shorter in the 1960s through 1970s. Children in Japan ceased to grow taller by the end of the 1980s, not because they quit taking more animal-sourced foods, meat and milk, but because they had drastically steered away from fruit and vegetables in their diets since the end of the 1970s. Having largely con-verged economically with Japan, South Korean children ceased to grow any taller in the mid-2000s. More importantly, it was discovered in this study that successive cohorts in South Korea started to fall gradually but steadily in height growth velocity from 1 st graders in middle school, aged 12 years to 3 rd graders in high school, and aged 17 years, to be once again 3 cm below their Japanese peers in the early-2010s. Analysis of Korea Household Expenditure Surveys classified by age groups of household head, decomposed by the author, revealed that children under 20 years of age in South Korea began to steer away from fruit and, particularly, vegetables in their at-home consumption in the mid-1990s, to average only 15% of the level of older adults in their 50s in the mid-2010s. These results lend supports to the importance of fruit and vegetables as determinants in height and its growth velocities in two ge-netically similar nations over time and stages of economic


Introduction
In the arena of economic history, human height has been widely held to represent standards of living in the society [1]. Comparing mean height of high school seniors, Japanese were a few cm taller than South Koreans in the 1960s through the early-1980s but overtaken by the latter by a few cm in the mid-2000s ( Figure   1). In the beginning of the 1990s, Japan's economy suddenly fell into a decades' long recession, with normal growth resuming only in the mid-2010s, whereas South Korea maintained rapid and steady economic progress over the same period.
Thus, per capita disparity in net GDP between the two countries has sharply narrowed during the past three decades. When purchasing power parity is taken into consideration, South Koreans may be enjoying almost the same standard of living as Japanese at the end of the 2010s. No doubts remain, but South Korea was still considerably behind Japan in respect of living standards in the early-2000s [2]. The statistical fact that Korean teens were a few cm taller than their Japanese peers in the mid-2000s could be attributed to alleged ethnic difference [3]. On the other hand, for decades South Koreans' diets, differed from those of the Japanese: appreciably more rice and vegetables; and less milk than in Japan, with nearly the same amount of animal meat only in recent years [4]. As a food economist, the author has attempted to explore the reversed differences in child height between the two countries in the past half century, with the tacit assumption of similarity of the two nations in ethnic endowments in stature [5].

Child Height Growth by Birth Cohorts
Secular changes in mean height of children in South Korea and Japan in the past half century have been identified by the author and his colleagues, with the utmost concern placed on the comparative analyses of mean height of fully-grown teenagers, i.e., high school seniors, 17 -18 years of age [4] [19]. In this paper, changes in height growth patterns of school children, from age 6 to 17, mostly boys, will be analyzed and compared between South Korea and Japan since the mid-1960s to the mid-2010s.

This may have caused apparent declines in height growth velocity of South
Korean adolescents, statistically observed since the late-1990s, as was the case with their Japanese peers, since the end of the 1970s, which was coincided with the wakamono no kudamono-banare [25] (steering away from fruit by the young) in Japan.

Brief Conclusions
South Korean high school seniors (boys aged 17) were 2 -3 cm shorter than their Japanese peers in the 1960s through the 1970s. The differences were, however, close to zero by the mid-1990s and South Koreans outgrew Japanese peers by 3 cm in the mid-2000s. Both countries made remarkably fast economic progress in the post-war era, beginning with South Korea distinctly behind Japan, and converging at the end of the 2010s. In terms of GDP per capita, Japan was still twice as large as South Korea in the mid-2000s, with appreciably more animal proteins in their diets than the latter. Household surveys decomposed into age groups of household members show that younger generations in Japan started to steer away from fruit and vegetables at-home consumption in the mid-1970s.
After converging and surpassing their Japanese peers, male high school seniors in South Korea ceased to grow taller in the mid-2000s and even began to decline slightly in mean height since the early-2010s, with growth velocities from 1 st graders in middle school to high school seniors falling steadily as much as 6 cm from the late-1990s to the early-2010s. When the author decomposed the household expenditure surveys classified by the age groups of household head, he was astonished to discover that children and young adults in South Korea started to steer away from vegetables, not meat, in their household food consumption. In the mid-2010s, children under 20 years of age are estimated to eat less than 15% of vegetables than the control group of 50-year-olds in the mid-2010s. As the Dutch national diet guidelines recommend, an adequate intake of fruit and vegetables is essential to activate protein intakes in food consumption [27].