Why the height of adolescents vary according to their nationality?

A team of researchers from Imperial College London found disparities of up to 20 cm in adolescents’ height, which varied according to their nationality, and analyzed the causes.

For a large study, published in The Lancet, researchers at Imperial College London looked at height differences in nearly 50 million children and adolescents, from their five to 19 years of age, in nearly 200 countries. A gap of up to 20 centimeters was found between 19-year-old participants from various nations.

The researchers notably dusted off 2,181 reports devoted to the evolution of young people’s height and body mass index over the period between 1985 and 2019.

The biggest and the smallest

Among the 19-year-olds, the tallest young people are of Dutch origin (183.8 cm on average for boys and 170.4 cm for girls). The Icelanders and Montenegrins follow them.

The smallest young men live in East Timor (160.1 cm on average), while the shortest young women are the Guatemalans (150.9 cm).

This represents a disparity of 20 cm in the extreme values.

“The 19-year-olds who were on average the shortest in 2019 lived in the south and southeast Asia, Latin America, and East Africa: Timor-Leste (160·1 cm, 158·0–162·2), followed by Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala (150·9 cm; 149·4–152·4), followed by Bangladesh, Nepal, and Timor-Leste for girls. The 20 cm or higher difference between countries with the tallest and shortest mean height represents approximately 8 years of growth gap for girls and approximately 6 years for boys.”

France

19-year-old French teenagers turn out to be the same size as 16-year-old Dutch, and teenage girls are the size of 14-year-old Dutch girls.

In 2019, French women’s average height increased from 163.2 cm (1980 value) to 164.5 cm. However, average adolescents from other countries have grown more, and France has fallen from 35th to 45th place among the countries evaluated according to this criterion.

Reasons

The factors on which this difference depends are food, a favorable economic and health situation, indicating the study’s authors.

Case study: in 30 years, China has experienced a significant improvement in living standards. As for height, the correlation is eloquent: 19-year-old young men grew 8.1 cm (up to 175.7 cm), and young women at this age 6.1 cm (up to 163, 5 cm on average), according to data collected for the year 2019.

What about genetics?

The lead author of the study, Andrea Rodriguez Martinez, confirms the species’ lesser role in genetics.

“We have also observed that the size of populations of immigrant descent tends to converge within a few generations with that of the new country, which reinforces the idea that genetics play only a small role in relation to nutrition or ‘environment,’ she said.

On the other hand, establishing “nutritional programs targeting early childhood and the school period covering almost the entire population” characterizes the countries that have recorded significant gains in size.

Decreasing size

In Sierra Leone, the Democratic Republic of the Congo, or in Burundi, there has been a decrease in the height of boys since 1980.

The height of children at age 5 in South Africa, Chile, or the United Arab Emirates is in line with World Health Organisation (WHO) references, but no longer when they are of school age.

“Pacific island countries in Oceania had the highest mean BMI in the world in 2019, surpassing 28 kg/m2

for 19-year-olds in many of these nations (figure 3A). Late-adolescence BMI was also high for boys and girls in Middle Eastern and North African countries such as Kuwait and Bahrain; in Caribbean islands such as the Bahamas; in Chile, the USA, and New Zealand; and, for girls, in South Africa.”

“The mean BMI of 19-year-old boys and girls was lowest (approximately 21 kg/m2 or lower) in countries in South Asia (e.g., India and Bangladesh), southeast Asia (e.g., Timor-Leste), and east and central Africa (e.g., Ethiopia and Chad), as was it for 19-year-old girls in Japan and some central European countries (e.g., Romania and Bosnia and Herzegovina).”

The highest and lowest worldwide BMIs were approximately 9–10 kg/m2 apart, equivalent to about 25 kg of weight.

Researchers, therefore, emphasize the need for good nutrition to ensure adequate development during childhood and adolescence.

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