What decides your height?

The height a person reaches as an adult depends on the genes they inherit from their parents as well as general health and nutrition during their years of growth. The child of short parents is more likely to be short themselves than the child of tall parents. There is a lot of variation; 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.  

Illnesses or poor nutrition during childhood or being small or premature at birth may mean children do not reach their full potential adult height. 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. 

Normal growth

The fastest period of growth is before birth, with the baby growing from almost zero to a length of about 50cm in nine months. This speed falls after birth with an average growth of 5.5cm per year at eight years old. During puberty, growth speeds up again. This is called the pubertal growth spurt. Before puberty, boys and girls grow at similar speeds, but during puberty boys grow more than girls. The average height of an adult man is 14cm taller than the average height of an adult woman.

Bones increase in length because of growth plates in the bones called epiphyses. As puberty progresses, the growth plates mature, and at the end of puberty they fuse and stop growing. The whole of the skeleton does not stop growing at the same time; hands and feet stop first, then arms and legs, with the last area of growth being the spine. Growth slows down and stops when a child has gone all the way through puberty and has reached an adult stage of development. This means that growth does not stop at a particular age, but children who are ‘early developers’ will stop growing before late developers. After the growth plates fuse, there is no more increase in height, and we all then shrink gradually as we get older.

Normal growth is controlled by a number of hormones:

• Growth hormone, made in the pituitary gland, which is the most important factor
   
• Thyroid hormone
   
• Sex hormones, testosterone or oestrogen, which are important for growth during puberty

What is too tall or too short?

Normal height ranges can vary between continents, races or ethnic groups of people, so the height of a person who is medically or socially defined as ‘short’ or ‘tall’ can be different depending on where they live or their ethnic background.

Doctor measuring height of young girl.

There are also variations in the height of each individual population, and most people who are very short or very tall are completely healthy, but just at the top or bottom end of the normal range for that particular population. A medical problem that affects growth is more likely if a child is growing slower or faster than expected.

Causes of a child growing too slowly include:

• Deficiency of thyroid hormone or growth hormone.
   
• Conditions where the hormones controlling growth are normal but the skeleton does not respond normally. This can be caused by, for example, Turner syndrome and achondroplasia.
   
• An illness that can affect growth, for example, a child with a serious gut or chest problem may grow slowly because of this.

Almost everyone who is very tall is normal and has no medical problems. Marfan syndrome and Klinefelter's syndrome can cause very tall stature, and extremely rare tumours of the pituitary gland producing too much growth hormone can result in very rapid growth (gigantism). 

Who should see a doctor about their height?

A doctor should be consulted if a child is growing slower or faster than expected or appears to be particularly short or tall relative to other children of the same age. 

Can anything help to increase height?

If a child is not growing normally, the cause is normally investigated. Treatment for a medical condition or a hormone deficiency will help the child to catch up and grow nearer to their potential adult height. 

Once the skeleton has stopped growing, no medical (drug) treatments will increase height. A surgical procedure where the leg bones are sawn and then gradually stretched apart can increase the length of the bones and so increase height. Because there is a risk of complications like fracture and infection, this procedure is not normally performed to increase height in adults. 

What can growth hormone do?

Children - If tests show that a child is deficient in growth hormone, they can be treated with artificial growth hormone, which will help them to catch up and reach a normal height. Treatment using a normal dosage cannot make them grow to a taller adult height than they would have had if they had not had a growth hormone deficiency. Studies have shown that growth hormone can help to increase the final adult height of children with Turner syndrome, Prader-Willi syndrome, kidney failure and for some children who were of very low birth weight for their gestational age.

Most children who are short are completely healthy and do not have any medical cause for their short stature. There have been studies looking at whether these short children (with no underlying medical condition) would be taller if given growth hormone treatment. These studies have shown that growth hormone treatment in the shortest children will result in a slightly taller adult height. However, treatment is not given to short healthy children, because, in Europe, the very small increase in adult height is not considered to justify giving years of daily injections. 

Adults - Some adults with growth hormone deficiency have growth hormone treatment. This is because, in adults, growth hormone is important in maintaining muscle bulk, a healthy skeleton and normal energy levels. Treatment is to help these problems and not to increase height. Once growth has stopped and the growth plates are fused, growth hormone treatment will not change adult height.

There are many adults who would like to be taller and some who would like to be shorter. There are also many parents who are concerned that their children are too short or too tall. In most cases, the situation cannot be changed and should not be considered unnatural.

Height cannot be altered once someone has stopped growing. Treatment can only change the height of children in very limited circumstances, and, almost always where treatment is for an underlying medical condition.