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How tall? That depends upon 80% genes and 20% environment (Source: Getty Images)

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Why did the US lose the height advantage?

Tuesday 19th April 2016 2:09 pm

People in the US used to be among the tallest in the world, but now that honour goes to the Dutch. Dr Karl gets to the bottom of the slide in height.

You’ve got to love history — in its own way, it’s the “ultimate science fiction”.

History shows us the past in many ways, so why not use the literal measure of a man to see where we’ve been, and where we’re going.

Welcome to auxology — the study of height. Height is a general marker for many aspects of biological wellbeing, including life expectancy.

So riddle me this little mystery. For about two centuries, the Americans were among the tallest people on Earth, and back then, the Dutch were way down at the short end. What changed, so that today, the Dutch are the tallest people on Earth?

We think that height is (like many other human characteristics) due to a mix of nature and nurture. The current estimate is that it’s about 80 per cent genetic, and 20 per cent environmental.

The latest studies have examined the DNA of about a quarter-of-a-million people — and it appears that about 700 different genes in about 400 different locations help control height. These genes seem to operate in three body zones — the legs, the spine and head, and finally, the overall body.

But environmental factors can be very powerful. We have three major growing periods after you get born — a huge spurt when we are babies and infants, a little one around age six or seven, and another big spurt during puberty.

Obviously, diet and nutrition are important to reaching your full potential height. But if a well-fed child is abused or neglected, they can be stunted in height. For example, children would slow down their growth at boarding school, and then catch up when on holidays with their parents.

Education is another environmental factor that helps you grow taller and also should make your life better. For example, people who have more education tend to need social services less.

Another factor that led to increased height was the trend to smaller families. This meant that each child would get more of the family’s time and resources.

Height difference throughout history

History shows us some quite extreme height differences. Around the time of American independence, in the late 1770s, the American-born soldiers were over seven centimetres taller than their English equivalents.

In early 19th century England, the difference in height in the youth between the upper class and the lower class was an incredible 22 centimetres.

And then around the mid-1930s, the Americans dramatically slowed down their previously regular increase in height with each passing decade.

They didn’t recover it until the late 1970s — but then, with two oddities. First, their increase in height resumed, but at a much slower rate.

Second, it applied only to the whites — the adult height of American black people stood still.

We don’t fully understand the American slow-down in height, relative to the Europeans — but we have identified some factors.

The first and major factor was the general improving nutrition and health of the European population, associated with a simultaneous lowering of disease in the community. From around 1850 to 1900, in the cities there was a decrease in disease carriers, such as horse poo in the street, and pigs and chickens in the backyard. Industrial pollution began to drop. In housing, sanitary conditions began to improve, and there were increasing supplies of fresh food to the cities, especially milk.

But most importantly, around that time, there began the professionalisation of health services and public health programming.

The power of health

Government-sponsored health services began in Germany and Austria in the 1880s, Belgium, Denmark, France and Sweden in the 1890s, and the UK and Ireland in 1911.

The increasing income of families was another factor, allowing better and more food. For example, in the UK around 1900, about 60 per cent of working class income was spent on food.

Nutritionists have identified some 50 nutrients that are each essential for health and growth. Missing out on any of these subtly nibbles away from your overall health and ultimate height. (Just as an aside, let’s compare current European and American children’s diets. American children eat more meals outside the home, and this food is higher in fat and energy, but lower in essential micronutrients. Another surprising fact is that each year, 25 million Americans get emergency food rations.)

Now remember those lanky Dutch, the tallest people on Earth?

One factor unique to the Netherlands was the extensive nature of the free system supporting Dutch mothers from all social classes. All mothers could get advice on infant feeding, child nutrition and hygiene from a paediatrician.

But in the USA, the expensive health care system with its weak safety net means that full and complete medical care has been effectively denied to both the children and adults in a large proportion of the population. For example, half of sicker adults in the US did not see a doctor when sick, or did not get recommended treatment, or did not fill a prescription because of cost.

So while the USA might be at its height as a military and economic super power, that doesn’t translate to its citizens standing taller than the rest of us.

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This blog first appeared on Dr Karl's Great Moments in Science

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