||日本における青少年の身長の推移 : 食料消費の観点から
Secular Trends in Body Height of Children in Japan : Food Consumption Perspectives
84 , 2016-11-30 , 専修大学経済学会
Overview : Why Have Japanese Youths Stopped Growing Taller in Body Height? (Hiroshi Mori)
<Preface>Many Japanese, the older generations in particular, may presume that the westerners (seiyoujin) are (on average, to be omitted hereafter) substantially taller in height than Japanese, who belong to the north - east Asians. Sitting around the international conference table, for example, all attendees look to be the same in height, whereas people from America or north Europe tend to prove a head taller than the Asian attendees, when standing up after the conference. The westerners have longer legs and arms than the Asians and have different hair colors and facial characteristics. Until a few months ago, the author was not aware of the fact that Dutch conscripts were 166cm in mean height in the last quarter of the 19[th] century, 5-6cm shorter than young Japanese currently (Steckel, 1995;Hatton, 2013; Mori, June,2016;etc.).Dutch male adults in their early 20s have kept growing at a speed of 2cm per decade since the end of the 19[th] century to 184cm in the end of the 20[th] century, becoming the world's tallest, closely followed by those in Norway, Sweden, and Denmark in the northern Europe. On the other hand, of those in the southern Europe, Portuguese and Italians have been substantially slower in growth (Larnkjaer, et al.,2006). Many researchers in various fields, including clinical-nutrition, anthropology, epidemiology, economic-history, etc., have participated in exploring the major determinants of the growth in stature and the differences in growth speed and patterns observed in various parts of the world (Rona, 2000;Silventonien, 2003;Hass and Campirano, 2006;Hatton and Bray, 2010;Hatton, 2013;Baten and Blum, 2014;Grassgruber et al., 2014 and 2016; Moradi and Hirvonen 2016;etc.).The subsequent short note, drafted in Japanese, is intended to contribute to the discussions regarding the developments of human stature by comparing the secular changes in height of children before reaching maturity in two neighboring countries, Japan and South Korea, in the past half century. It has been widely recognized that the decreases in the infant mortality (Schmidt et al., 2015;etc.) and the intake of high quality proteins such as milk and dairy products and meat should be major determinants of a positive height trend (Baten and Blum, op.cit.) and plant protein from wheat and rice negative ones (Grasgruber et al. , 2014;2016;etc.).The young adults in both countries kept growing very rapidly (at a speed of 2cm per decade), but then the advance in height stopped. Japanese boys, age 20, were 162cm in 1950, 167.5cm in 1975, and 171cm in the mid-1990s and have stopped growing any taller since then. Their Korean peers were 168cm in 1975, 173cm in 1997 and still kept growing taller to 174.4cm in the mid-2000s and ceased to grow since then. Why these differences? The infant mortality rates have been very close to zero for some time in the two countries. Even in the mid-2000s, Japan was higher in per capita consumption of milk and meat, and much lower in rice consumption than Korea, respectively (Grasgruber, 2016, Fig.9). Predicted male height, based on "nutrition + socioeconomic variables" for Japan and S. Korea are estimated at 174.5 and 172.0cm, respectively, whereas observed values are 172.1 and 174.3cm, respectively (ibid. Fig.12). Explaining this anomaly may require further research.
<Short Concluding Remarks>A group of researchers at the Fruit Tree Science Institute in conjunction with the Hamamatsu University School of Medicine have been engaged in longitudinal studies of the residents in Mikkabi-cho, known for their production of mandarins. One of the findings they reached after nearly a decade of cohort studies is that intakes of fruits, mandarins in particular, have high positive associations with bone mineral density for post-menopausal female subjects, remarkably reducing the risk of osteoporosis. In their study reports, they refer to several studies conducted overseas which ascertained the positive associations between fruit and vegetable intakes and bone mineral density for the subjects of adolescents (McGartland et al., 2004;Prynne et al.,2005;etc.).We suspect that radical decline in the consumption of fruit, mandarins, in particular by the Japanese youths in the past some 30 years (Mori et al., 2009;Mori and Stewart, 2011; etc.) might have something to do with the observed cease in height growth of Japanese youths, as compared to their peers in S. Korea, where per capita consumption of fruit, tangerine in particular, has been soaring during the same period of time.