Why are some children taller? Diet a bigger factor than genes
A recent study published in medical journal The Lancet suggests that, while genetics play a part in the height of a person, nutrition and the environment can play a bigger role. Within a few generations, the height of migrant descendants typically catches up to the height of non-migrant children in their new country.
The study, which came out this month, analyses the physical growth of children in different countries by pooling height and body mass index data from 193 countries.
It notes that teenagers in China have achieved significant gains in height over the past 35 years.
In 1985, the mean height of 19-year-old women in China was 157.4cm (5.2 feet) and that of 19-year-old men 167.6cm. In 2019, the corresponding figures were 163.5cm and 175.7cm respectively. According to the study, the increase in boys’ height in China is the largest in the world and the increase in girls’ height is the third largest.
Previous research has shown that economic development in China in the past four decades has reduced childhood malnutrition. However, growing inequality has also seen children living in rural areas of China lag behind their urban peers in nutrition intake and height.
According to a 2014 study published by the World Health Organisation, the more developed regions of China are also experiencing a rise in childhood or adolescent obesity thanks to greater access to sugary snacks and fast food.
The Lancet study compares the changes in body mass index (BMI) of children and adolescents globally. Countries that have the highest BMI for both genders include the United States, New Zealand and Kuwait, while countries with the lowest include India, Bangladesh, East Timor, Ethiopia and Chad.
It also estimates there is a 20cm difference in mean height between 19-year-olds in the tallest and shortest nations. Countries with the tallest adolescent populations include the Netherlands, Montenegro, Estonia and Denmark.
Despite their growth spurt in the past 35 years, 19-year-old men in China are, on average, 8.1cm shorter than their counterparts in the Netherlands. Women are 6.9cm shorter.
Emerging economies, including China, have seen the biggest gains in children’s height, but in many countries in Sub-Saharan Africa, the height of children has stayed the same – or even dropped.
Overall, girls in South Korea, Vietnam, Saudi Arabia, Turkey and some Central Asian countries, and boys in central and western Europe, had the healthiest changes in body growth status over the past three-and-a-half decades because they had a much larger gain in height than they did in BMI.
Having low height and low BMI is associated with increased risk of morbidity and mortality, impaired cognitive development, and poorer educational performance and work productivity in later life.
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High BMI comes with a higher risk of disability and premature death in adulthood, as well as poorer mental health and educational outcomes, The Lancet study says.
Researchers therefore recommend policies to support healthy growth for young people, such as implementing free school meal programmes and applying restrictions on how much processed carbohydrates a child should eat.
This article was first published in South China Morning Post.