Lack of secular trend in adult stature in white South African males born between 1954 and 1975

Abstract

The object of this study was to determine whether there was a secular trend in the body height of white South African males born between 1954 and 1975. The survey used the body heights of conscripts, measured between 1990 and 1991 at South African Defence Force training camps. The participants comprised 21264 healthy white South African male conscripts from the National Serivce intakes of July 1990, January 1991, and July 1991. The measurements were analysed by establishing the averages and standard deviations of the adult body heights by year of birth. It was found that there was a decrease of the measured stature with the year of birth. For instance, those conscripts born between 1954 and 1962 were handled as one group (n = 36) and their average height was 1793 mm (s = 79). The heights of those born in 1967 (n = 385) and 1972 (n = 5168) were 1800 mm (s = 69) and 1776 mm (s = 69) respectively. The 9 conscripts born in 1975 were 1749 mm tall (s = 73). the apparent decrease in stature of younger conscripts can be attributed to the fact that some males continue to grow into their late twenties. Thus the raw data were corrected by adding an appropriate number of millimetres to the average stature, e.g. 6 mm to that of the 24 year olds, 14 mm for the 19 year olds, and 59 mm for the youngest (HULANICKA and KOTLARZ 1983). These additions resulted in similar body heights for all conscripts: 1806 mm, 1790 mm and 1808 mm for those born in 1967, 1972 and 1975 respectively. It was concluded that the secular trend in body height of S.A. white males was either negative or absent. The living conditions of most white South Africans were improving during this period. There is a strong positive secular trend amongst conscripts in Europe born at a similar time. Furthermore, the European conscripts were taller than our subjects, e.g. the adult stature of Dutch conscripts born in 1966 was 1835 mm. The lack of a secular trend in South Africa therefore cannot be explained by the attainment of the so-called genetic potential.