The average height of adults born in a given year (cohort) is based on the disease environment that birth cohort faced in early childhood. In poor countries, it may also be an indication of insufficient availability or diversity of nutrients. How do you think this applies to Latin America?
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To see whether some of these patterns are found in Latin America, I carried out some calculations based on data on adult height of women mainly drawing on the Demographic and Health Surveys (DHS) for groups born between 1950 and 1990 in nine countries: Bolivia, Brazil, Colombia, Dominican Republic, Guatemala, Haiti, Honduras, Mexico and Peru. For three of these countries (Brazil, Colombia, and Mexico) I also have data on the height of adult men. Results show that height has been increasing in all countries (with the possible exception of the Dominican Republic).
On average, across all countries, women born one year later are 0.076 centimeters taller than those born one year earlier. Over a forty-year period, this amounts to an increase in average height of about 3 centimeters. Similar patterns can be found for men in Brazil, Colombia, and Mexico.
Adult Height determined in Early Childhood
For researchers, using height as an early measure of exposure to the disease environment in early childhood is complicated because there are two offsetting effects.
- There is a selection effect: the weakest children die early on but, had these children survived, they would on average have been shorter than other children born in the same year.
- There is a scarring effect: for those who survive childhood, early exposure to disease leads to inflammation and this, in turn, reduces height in adulthood.
These two effects (mortality selection and scarring) can result in surprising patterns. A high mortality population can be tall because of the selection effect. As the disease environment improves somewhat, the scarring effect may begin to dominate, so that height falls. Finally, as countries progress further, and infectious diseases, among other factors, become relatively unimportant, improved conditions in childhood will result in taller individuals in adulthood.
Another example: Adult Height in European Countries
Some studies such us “Adult Height and Childhood Disease” report interesting patterns mainly drawn from the record of heights of thirty one birth cohorts (1950-1980) from England, the United States, and ten continental European countries. Infant mortality has been falling and adult height has been increasing in all countries. The declines in infant mortality and the increases in height generally occurred for people from the sample who were born the same year in each country.
The finding that people from groups with higher mortality at early ages also tend to be shorter, on average, has also been reported in another study that uses historical data (mainly from the 19th century) for England, France, Sweden and Switzerland. In addition, this study shows that average mortality in old age for each birth cohort is more highly correlated with childhood mortality (which captures the disease environment in childhood) than it is with concurrent childhood mortality for that cohort (which would capture conditions at the time of old age, including, for example, average income levels at the time).
Based on the results, circumstances in early childhood matter more than circumstances in old age in determining not only cognitive development and language, but also adult height and mortality among the elderly.
What do you think about the results?
Norbert Schady is the Principal Economic Advisor for the Social Sector at the Inter-American Development Bank (IDB).