LIFE (elifesciences.org) produced a research article discussing trends in human height spanning over a century (July 26, 2016). We shall heavily draw upon the article below - even paraphrase - for two reasons. First, the findings show that child malnutrition matters for income generated in adulthood and secondly, average height of a population could change over time.
First, a few words on the advantages of tallness. Available empirics, both from medical and social sciences, tend to argue that being taller is associated with enhanced longevity, lower risk of adverse pregnancy outcomes and cardiovascular and respiratory diseases, and higher risk of some cancers. Besides, there is also evidence that taller people on average have higher education, earnings, and possibly even social position.
"Although height is one of the most heritable human traits, cross-population differences are believed to be related to non-genetic, environmental factors. Of these, foetal growth (itself related to maternal size, nutrition and environmental exposures), and nutrition and infections during childhood and adolescence are particularly important determinants of height during adulthood.
Information on height, and its trends, can therefore help understand the health impacts of childhood and adolescent nutrition and environment, and of their social, economic, and political determinants, on both non-communicable diseases (NCDs) and on neonatal health and survival in the next generation".
The eLIFE's research observed that people born in 1896 were shortest in Asia and in Central and Andean Latin America. For example, the 1896 male birth cohort on average measured only 152.9 cm in Laos, which is the same as a well-nourished 12.5-year-old boy according to international growth standards. This was followed by Timor-Leste and Guatemala. Women born in the same year in Guatemala were on average 140.3 cm, the same as a well-nourished 10-year-old girl. El Salvador, Peru, Bangladesh, South Korea and Japan had the next shortest women. The tallest populations a century ago lived in Central and Northern Europe, North America and some Pacific islands. The height of men born in Sweden, Norway and the USA surpassed 171 cm, 18-19 cm taller than men in Laos. Swedish women, with average adult height of 160.3 cm, were the tallest a century ago and 20 cm taller than women in Guatemala. Women were also tall more than 158 cm in Norway, Iceland, the USA and American Samoa.
Changes in adult height over the century of analysis varied drastically across countries. Notably, although the large increases in European men's heights in the 19th and 20th century have been highlighted, the paper found that the largest gains since the 1896 birth cohort occurred in South Korean women and Iranian men, who became 20.2 cm and 16.5 cm taller, respectively. As a result, South Korean women moved from the fifth shortest to the top tertile of tallest women in the world over the course of a century. Men in South Korea also had large gains relative to other countries, by 15.2 cm. There were also large gains in height in Japan, Greenland, some countries in Southern Europe (e.g., Greece) and Central Europe (e.g., Serbia and Poland, and for women, Czech Republic). In contrast, there was little gain in height in many countries in sub-Saharan Africa and South Asia.
The research argues that the pace of growth in height has not been uniform over the past century. The impressive rise in height in Japan stopped in people born after the early 1960s. In South Korea, the flattening began in the cohorts born in the 1980s for men and it may have just begun in women. As a result, South Korean men and women are now taller than their Japanese counterparts. The rise is continuing in other East and Southeast Asian countries like China and Thailand, with Chinese men and women having surpassed the Japanese (but not yet as tall as South Koreans). The rise in adult height also seems to have plateaued in South Asian countries like Bangladesh and India at much lower levels than in East Asia, e.g., 5-10 cm shorter than it did in Japan and South Korea.
Male and female heights were correlated across countries in 1896 as well as in 1996. Men were taller than women in every country, on average by 11 cm in the 1896 birth cohort and 12 cm in the 1996 birth cohort. In the 1896 birth cohort, the male-female height gap in countries, where average height was low, was slightly larger than in taller nations. In other words, at the turn of the 20th century, men seem to have had a relative advantage over women in undernourished compared to better-nourished populations. A century later, the male-female height gap is about the same throughout the height range. Changes in male and female heights over the century of analysis were also correlated, which is in contrast to low correlation between changes in male and female.
Change in population mean height was not correlated with change in mean BMI or Body Mass Index across countries for men (correlation coefficient = 0.016) and was weakly inversely correlated for women (correlation coefficient = 0.28). Countries like Japan, Singapore and France had larger-than-median gains in height but little change in BMI, in contrast to places like the USA and Kiribati where height has increased less than the worldwide median.
Over the past century, adult height is believed to have changed substantially and unevenly in the world's countries; there is almost no indication of convergence across countries. The height differential between the tallest and shortest populations was 19 cm for men and 20 cm for women a century ago, and has remained about the same for women and increased for men a century later despite substantial changes in the ranking of countries in terms of adult height.
"In particular, South Korean and Japanese men and women, and Iranian men, have had larger gains than European men, and similar trends are now happening in China and Thailand. These gains may partially account for the fact that women in Japan and South Korea have achieved the first and fourth highest life expectancy in the world. In contrast to East Asia's impressive gains, the rise in height seems to have stopped early in South Asia and reversed in Africa, reversing or diminishing Africa's earlier advantage over Asia."
The writer is a former Professor of Economics at Jahangirnagar University.
abdulbayes@uyahoomail.com
On human height
Abdul Bayes | Published: August 23, 2016 00:00:00 | Updated: February 01, 2018 00:00:00
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