Genes – The DNA blueprint for height

A lot of a person’s height depends on the genes they inherit from their parents – about 80% of our height is genetically determined. If parents are tall, then there is a good chance they will have tall children; if parents are short, then they are more likely to have short children. The adult height someone should expect to achieve genetically is called the ‘Mid-Parental Height’. This can be worked out by measuring the height of both parents, adding the results together and dividing by two, and then to this number adding 7.5cm for a boy, or taking away 7.5cm for a girl. But there is a lot of variation, so brothers or sisters with the same parents will not all end up the same height and parents can, by chance, have a child who is unexpectedly tall or short in relation to the rest of the family.  

Nutrition – The Fuel for growth

While genes set the stage, food is important to keep growth going. A balanced diet with vitamins, minerals, proteins and other nutrients is needed for someone to reach their full height potential. The average height of the population has gradually increased over the centuries because children have been better nourished and have had fewer illnesses and infections. Poor nutrition in childhood, either from not having access to adequate, healthy food, or because of illnesses that affect absorption of that food may mean children do not grow as much as they should.

Hormones – The body’s signals for growth

Hormones are the chemical messages that move through the body, telling it to grow. The important hormones for growth include: growth hormone, which is made by the pituitary gland; sex hormones such as oestrogen and testosterone; and thyroid hormone. Growth hormone is what drives growth in children – so that the average primary school child grows 5cm per year. Oestrogen and testosterone are important during puberty, when both girls and boys have a growth spurt, and may grow 8-9cm/year on average. Girls have their growth spurt on average two years before boys, and usually six months before menarche (when menstrual periods start).  

During all this growth, bones increase in length because they have growth plates where new bone can form. As puberty progresses, those growth plates mature, and eventually fuse and stop working. After the growth plates fuse, bones can no longer grow and there is no more increase in height. 

Sleep – Magic time for growth

Most growing happens when you sleep. That is why getting enough sleep is important, especially in teenage years – so most experts say teens need eight to ten hours sleep each night.

The Environment – the setting for growth

The environment where people live also has an impact on growth. Living in a place with clean air, access to good healthcare and a healthy lifestyle will mean you are likely to grow better than someone who doesn’t have access to these things. Even stress can affect growth so having a supportive environment is important too.

But could it be a medical issue affecting height?

As we have said, there are can be lots of reasons that height can vary and these people can be completely healthy. But sometimes there can be medical problems that mean someone can grow more or less, or faster or slower than expected. 

Doctor measuring height of young girl.

Small (but perfectly formed?) –why may someone grow slowly or not enough

Most often when a parent is worried that their child isn’t growing tall or fast enough it is due to their genetics, or a normal but slightly delayed puberty. Sometimes giving time for puberty to kick in, or understanding how tall you are likely to be because of your genes, is all that is needed. But occasionally there are issues that stop people growing like normal.  

Sometimes there can be a problem with hormone production – such as growth hormone or thyroid hormone deficiency, or pituitary problems from tumours, or radiation to the brain. There are also some conditions where hormones are produced normally but the skeleton doesn’t respond to them normally– for example in Turner’s syndrome or achondroplasia (sometimes called Dwarfism). There are other genetic conditions where children have a short stature, like Prader-Willi syndrome and SHOX deficiency, a condition where people have marked shortening of the forearm and lower legs.

Significant childhood illness can slow growth, like kidney failure, or a serious gut or chest problem. Also, some children who are born prematurely do not grow as tall as expected.

Reach for the stars –why someone may be unexpectedly tall

For the majority of tall people, their height simply reflects their unique genetic blueprint. Rarely, the body produces too much hormone – for example ‘gigantism’, where too growth hormone is produced by the pituitary gland. Some genetic conditions, such as Marfan syndrome and Klinefelter's syndrome, can cause individuals to grow very tall. And some children start producing sex hormones early (‘precocious puberty’) and so they can grow faster and earlier than their peers, though often they stop growing sooner than their friends as well as their bone growth plates fuse quicker, and they do not end up taller than expected.  

Who should see a doctor about their height?

It is sensible to see a doctor if a child is growing slower or faster than expected or appears to be particularly short or tall compared to other children of the same age. 

How can I make myself taller?

In a child with no medical problems, making sure they have a good diet, regular exercise and plenty of sleep will help them reach their full potential height. If there is an underlying medical condition, then often treating this can help a child to grow more. However, once the growth plates in bones are fused, no drug treatments can help someone grow taller.  

It is possible for someone to have surgery to gradually increase their leg length – the leg bones are sawed in two, and gradually stretched apart with new bone growing in between – but this is a complex procedure with potential complications such as infection and blood clots, so is not usually recommended.

What about hormone treatment?

If tests show that a child has growth hormone deficiency, then treatment with synthetic growth hormone can help their growth catch up and they can reach their expected height – but it won’t make them taller than their genetic blueprint suggests. Growth hormone treatment can also help growth in children with other medical issues such as chronic kidney disease, Turners’ syndrome, or those born at a very small size.

In children who are healthy and have no medical cause for their short stature, growth hormone can cause a slight increase in height – but on average that increase is less than 5cm. In the UK, growth hormone is not recommended for short but healthy children because it is felt that the years of daily injections does not justify this small increase in height.

In children where puberty is delayed or does not happen, then giving hormones such as testosterone and oestrogen can bring on the pubertal growth spurt. However, these hormones do also cause the bone growth plates to fuse, so the effect on height is limited.

In adults, growth hormone therapy won’t cause any increase in height, even in individuals with growth hormone deficiency, because their bones are already fused. However, growth hormone can help with building muscle, keeping a healthy skeleton, and maintain normal energy levels.

Fun facts about height

Robert Wadlow holds the Guinness World record for being the tallest person ever recorded, at 272cm (8ft 11.1 inches).  Until 2020, if you wanted to be a pilot in the US Air Force, you had to be 163-196cm (5 foot 4 inches to 6 foot 5 inches) tall. Gravity compresses us, so astronauts grow taller in space as they don’t experience the normal effects of gravity for months at a time.