The Secular Improvement in Height, Weight, and Chest Girth, 1901-1985

The anthropometric measures consist of a complex of related measures of physique: height, weight, weight for height (BMI, the body mass index, defined as weight in kilograms divided by the square of height calculated in meters), chest girth, and so forth. The most commonly utilized of the measures is (standing) height.^[1] The widespread use of height as a measure of the standard of living in the field of anthropometric history reflects the fact that for the last several centuries figures on height have been collected and published by and for the use of military organizations in a number of countries (see panel A of table 2). The degree

to which military data is representative of the terminal heights of young adult males is a matter of debate in particular cases (see the special methods developed by Flood, Walter, and Gregory [1990] to handle British data of this sort). But the fact remains that even when one discounts for problems of measurement, there are clear secular trends in adult height for the United States and select European countries. Indeed the estimates marshaled in panel A of table 2 suggest that while heights for males in the United States did not rise appreciably, heights in the Scandinavian countries showed a dramatic increase. Figures for male schoolchildren aged eighteen in Japan show increases that in percentage terms are comparable to those for Scandinavia. For instance, comparing the figures in panel B.1 of table 2 for the years 1981-1985 with those for 1901-1985, it is apparent the percentage gain in height for males is about 6.6 percent, which is roughly equivalent to the percentage gains for Sweden and Norway recorded over a historical period that is almost twice as long.

To a degree the figures on height suggest that the population has "caught up" with Western Europe or at least closed the gap that once existed. However, one must be careful in asserting this. A gap still remains; on average in 1985 males in Japan tended to be shorter than males in most Western European countries. During the 1981-1985 period height for males in Japan averaged about 170 centimeters. These average levels were reached by males in select European countries and the United States at the following dates: United States, 1715; Sweden, 1913; Norway, 1927; Denmark, 1930; Holland, 1950; France, 1960; and Italy, 1977 (Floud, Wachter, and Gregory 1990:26). Whether this increase in heights in Japan will continue and whether the gap will ever be eliminated is, of course, a matter that we cannot resolve here. But one point that was raised in chapter 1 must be kept in mind: the gene pool has a definite effect on standing heights in Japan. Note from the figures in panel B.2 of table 2 that most (but not quite all) of the gain in standing height has been due to a gain in leg length. As can be seen, the ratio of sitting-to-standing height has been declining as legs have become longer.

The other point that can be readily gleaned from a perusal of the figures for Japan in table 2 is the dominance of secular change in tempo over secular change in level. I give figures on ages 6 and 12 as well as on age 18 both to capture the dynamics of the growth spurt and to take advantage of the six-year differences between the ages. Creating a six-year standard interval is of considerable utility to the statistical analysis

taken up in section 2.4, but an additional benefit can be immediately grasped here. We can calculate the gain in average height for persons aged 12 in a given year t and the same cohort of persons aged 6 in year t - 6. That is, we take the average height for persons aged 12 in year t and subtract from that the average height for persons aged 6 in year t - 6 in order to estimate the gain for the cohort in year t - 6. A secular trend toward earlier maturation, that is, a downward drift in the mean age of the growth process and in the adolescent growth spurt in particular, can be seen from the fact that the anthropometric measures at age 6 and age 12 increase disproportionately in comparison to the gains at age 18. For instance, the percentage gains in height over the 1901-1910/1981-1985 period at age 6 is 8.8 percent and at age 12 is 12.2 percent. The fact that mean age of the growth spurt is shifting downward means that the secular trend in the gains in the anthropometric measures between age 6 and 12 is unusually great. For instance, the age 6 to age 12 gain in centimeters averaged over the 1901-1910 period is 27.2 and the gain averaged over the 1971-1980 period is 34.4. In short, the secular trend in the tempo of growth in height up to age 6 dominates over the secular trend in levels of height at age 18. That is to say, the improvement in population quality can be discerned both in the trends in levels and in the trends in tempo.

The dominance of secular trends in tempo over secular trends in levels is even more evident for females than it is for males. Figures are given in table 3. The percentage increases in height levels over the 1901-1910/ 1981-1985 period for girls aged 6, 12, and 18 are 9.3 percent, 12.6 percent, and 6.4 percent, respectively. The percentage gain at age 18 for females is less than that for males at age 18, but the percentage gains at age 6 and at age 12 exceed the gains for males. The difference in secular changes in tempo is surely linked to the fact that females mature at younger ages than do males, which can be easily gleaned by comparing the gains between ages 6 and 12 for females with those for males. Note that the increase in the amount of the gains from ages 6 and 12 between 1901-1910 and 1971-1980 is identical for both sexes (7.2 cm) and that the gains are always larger for females than for males. Note also that gains between ages 12 and 18 are far larger for males than for females. This reflects both earlier maturation for females and the fact that terminal average adult heights for females are less than those for males. The secular decrease in gains in height for females aged 6 and 12 is an unusually dramatic indicator of the secular trend in the tempo of growth.

While the differences between males and females in terms of the tempo of growth in and levels of height are of interest, the main point I wish to stress is the similarity in the secular trends between the sexes. The correlations between levels of male and levels of female height at ages 6, 12, and 18 are very high: over the 1900-1985 period the correlations are +.997, +.99, and +.97, respectively; and over the 1900-1940 period the correlations are +.97, +.98, and +.96, respectively.

That trends in tempo and level differ somewhat in magnitude does not mean that the heights at the various key ages that we focus on here are not highly correlated. For instance, over the 1900-1985 period the correlation between heights for males at age 6 and 12 is +.98; at ages 6 and 18, +.99; and at ages 12 and 18, +.97. For females the correlations over the same period are somewhat lower: +.96, +.90, and +.91, respectively. That correlations are lower for females probably reflects the striking dominance of secular trend of tempo. It is interesting and useful to keep in mind that over the period 1900-1940 the correlations between heights at ages 6 and 12, at ages 6 and 18, and at ages 12 and 18 are lower than over the entire period 1900-1985. For instance, for males the correlations are respectively +.96, +.90, and +.91; and for females the correlations are respectively +.91, +.88, and +.92. A final point to keep in mind in considering both the differences and similarities between secular trends in the tempo and in the levels of human growth is the greater sensitivity of six-year gains in height to changes in nutrition and other components of per capita consumption. To see this consider figure 1, which graphs annual figures on an index for nutrition (described in the next section), heights for females aged 6, and six-year gains in height between ages 6 and 12. Notice that the drop in nutritional intake occurring in the late 1930s and early 1940s due to Japan's growing military involvement is clearly mirrored with a slight lag in the case of six-year gains in height but that the impact on height levels is far less pronounced. In sum, tempo dominates over levels in terms of secular trend; it is also a more sensitive barometer of changes in the factors underlying population quality. To be sure, individuals who are deprived in the short run may "catch up" later on and therefore the overall impact of a short-term diminution in net nutrition may not be long lasting. Nevertheless, insofar as we are interested in ascertaining the causal connection between net nutrition and population quality, the greater sensitivity of gains in height and gains in other anthropometric measures is an important point that must not be forgotten.

Figure 1.
Indexes of Nutrition, Height for Females Age 6 and Growth for Females
from Age 6 to 12

I have begun my discussion of secular trends in the anthropometric measures in Japan with figures on height because height figures are the ones that are most commonly encountered in anthropometric history. While I do make use of some Japanese military conscription data later on in this study and T. Shay (1994) makes extensive use of it in his study, the bulk of my data is for schoolchildren and comes from surveys conducted in schools by the Ministry of Education. Why do I favor the use of this data? First, it is more comprehensive than the military recruitment examination data: it covers both sexes; it includes figures on weight and chest girth; and it is available throughout both the 1900-1940 and postwar periods (the military draft in Japan ended after World War II, although Japan currently maintains a small self-defense force). Second, the data are available for a variety of ages under 18 and hence allow analysis of tempo effects that, as noted above, are far more sensitive to short-run fluctuations in net nutrition than are levels, especially adult levels.

Despite the compelling virtues of the data set analyzed here, there are defects in it which we must confront before proceeding further. Chart 2 provides a summary background for a general discussion of the data used not only in this section but throughout this chapter. At this junc-

ture I will concentrate on the anthropometric measures covered in panels A, B, and C of the chart. As can be seen, the figures are for schoolchildren, and therefore children in the relevant age groups who did not attend school are excluded. Who was attending school? This depends on the period involved. S. B. Levine and H. Kawada (1980: 48-52) note that by 1900 four years of schooling (typically from ages 6 to 10), made compulsory in 1886, was virtually universal in practice. In 1907 it was decreed that compulsory education be extended to six full years, although this requirement was not successfully enforced until 1918. However, the extent of underregistration should not be exaggerated. For instance, in 1910, 98.8 percent of males and 97.4 percent of females of compulsory school age were reported as attending school (Japan Statistical Association 1988: table 22-1, p. 212). It is thus reasonable to suppose that by the early 1900s most children aged 6 and 12 are covered in the Ministry of Education data set. After the war nine years of education was made compulsory (from ages 6 to 15), and by the 1970s most children in Japan were in fact graduating from high school, which means that the coverage of individuals aged 18 in the Ministry of Education data set is by and large universal for all three ages analyzed here. The problem, of course, is the potential bias resulting from the selectivity of enrollment of children over age 12 before that period.

As can be seen from panel A of chart 2, there is a potential upward bias in heights, weights, and chest girth for males and females aged 18; and the earlier the date, the greater the upward bias. The reason is that the earlier the date, the lower the advancement rate past age 12 in the school system, and as a result the greater the selectivity of the population of those examined by the Ministry of Education. It is demonstrated in Part II of this volume that there are socioeconomic differentials in the anthropometric measures: in general the higher the social and economic status one is born into, the greater the height, weight, and chest girth and the higher the probability of advancing past age 12 in the school system. But as advancement rates increased the extent of this upward bias began to fall. It is likely that there is a contrary tendency at work on heights, weights, and chest girths for individuals aged 18, a contrary tendency that may allow us to conclude that this declining upward bias does not present a major problem for our analysis. The reason for the existence of a contrary tendency lies in the declining mean age of maturation. While I use age 18 as my oldest age for analysis (since advancement rates in the educational system after age 18 are so low that we

cannot usefully employ data on persons over 18 as auxological indicators for the population at large), in fact growth does not necessarily terminate at age 18. But as the mean age of maturation declines, the proportion of the population that continues to mature after age 18 declines. Hence it is likely that the secular trend toward earlier maturation, according to which there is a declining downward bias in the anthropometric measures (the earlier the year, the greater the downward bias), does counteract the upward bias due to a decline in the selectivity of the population receiving an education through age 18. For this reason I feel relatively comfortable using data for all three ages, 6, 12, and 18. But I must caution the reader that the problem does exist.

Now to return to a point made earlier about the virtues of using a data set that allows us to measure and analyze a variety of anthropometric characteristics of Japan's population, let us turn to figures on weight and the BMI. Figures for males appear in table 4 and figures for females appear in table 5. The virtues of having data on weights for both males and females (not just males, as is usually the case when one is using military recruitment data) can be seen from a comparison of trends in the BMI for males and for females. For if we calculate percentage gains in weight for the period 1901-1910 to 1981-1985, we get the following figures for percentage increase in weight and the BMI.

Note that the increase in weight for females at age 18, contrary to the increase at ages 6 and 12, is far less than that for males. The reason cannot be physiological: as can be seen from table 5, this is almost entirely a postwar phenomenon. The obvious explanation is dieting, and the reason for dieting is the concept of beauty for women that places strong emphasis on being slender. (The concept of sacrificing potential physical work capacity for beauty is undoubtedly much more typical of the urban nonagricultural population than of the farming population for whom potential for work is a virtue among young women on the

marriage market. Hence it is not surprising that the trend is much more evident during the postwar period when the farming population has been rapidly dwindling than during the prewar era.) Thus the weight and BMIs of young adults were apparently shaped by a cultural rule that does not appear to have been operating for younger children. This is an additional argument in favor of using data for young children as well as adults. It should be noted, however, that height of females at age 18 appears to be unaffected by the practice of dieting. Correlations between measures of height and weight for males and females presented in panels B and C of chart 1 testify to differences between height, on the one hand, and weight and the body mass index, on the other, which must be kept in mind in interpreting the anthropometric measures as measures of population quality.

Trends for a third major auxological measure, chest girth, are explored in table 6. Particularly striking for females is the secular trend in tempo that overshadows the secular trend in levels. For instance, in comparison with 1901-1910 when the six-year gain in chest girth for girls aged 6 is 11.6 centimeters, the average six-year gain during the 1981-1985 period is 18.2 centimeters.

Finally, the figures on anthropometric measures in table 7 illustrate several points about the drawbacks and strengths of the data set for school children on which my analysis in this chapter rests and provide additional background about prewar trends in height.^[2] The following observation supportive of use of the data on schoolchildren leaps out at us. Trends in average height and weight for persons examined for conscription examinations are much less striking—indeed, the trends in averages are almost ambiguous—than are the trends we secured for schoolchildren. To be sure, it may be argued that truth may lie on the side of an ambiguous or uncertain trend and that, therefore, finding this trend in the military recruit data is a virtue and not a deficiency. But there are reasons for thinking that the figures on schoolchildren more accurately represent the true underlying pattern. To see my point, note that the figures on percentages "small" (defined as 150 cm or less) and on percentages "tall" (defined as 170 cm or more) point toward an unfaltering increase in height that is consistent with what—using averages—we have found for male schoolchildren. Indeed, the fact that moments of the distribution of heights other than averages are available for military recruits is one of the most attractive features of the military recruitment data. But the shortness of the time period for which the data on distribution of heights is available (1915-1940), the lack of figures

on females, the absence of any measurements capturing the timing of the growth spurt, and so forth, make sole reliance on these data alone problematic. I do make use of them to a limited degree in Part II of this study.