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Lactose intolerance

This factsheet is for people who have lactose intolerance, or who would like information about it.

Lactose intolerance is when your body is unable to break down lactose (a sugar found in milk).

About lactose intolerance

Lactose is a sugar found in milk and other dairy products. Usually, your body breaks it down into two simpler sugars, called glucose and galactose, by a chemical (enzyme) called lactase. Lactase is made in the inner lining of your small bowel. Once lactose has been broken down, it's absorbed from your bowel into your bloodstream.

Lactose intolerance develops when your body doesn’t make enough lactase. If you don't produce enough lactase, then you won’t be able to digest or absorb lactose properly from your bowel. When this happens, you get the symptoms of lactose intolerance.

Lactose intolerance usually affects older children and adults because your levels of lactase start to decrease naturally as you get older. Some children are born with lactose intolerance because they don't have any lactase at all from birth, but this is rare. Sometimes you can have lactose intolerance temporarily because the lining of your small bowel (where lactase is produced) has been damaged. This is called secondary lactose intolerance.

In the UK, around five in 100 people have lactose intolerance. It’s more common in countries where milk isn't part of the usual adult diet, such as South America, Africa and Asia.

Symptoms of lactose intolerance

The symptoms of lactose intolerance appear after you’ve consumed something that contains lactose – and include:

  • feeling bloated
  • stomach pains or cramps
  • diarrhoea
  • wind
  • bowel sounds that you can hear
  • feeling sick
  • an urgent need to have a bowel movement

These symptoms may be caused by problems other than lactose intolerance. If you have any of these symptoms, see your GP for advice.

Complications of lactose intolerance

If you have lactose intolerance and don’t include enough alternative sources of calcium in your diet, you’re bones may become weaker and you can develop a condition known as osteopenia.

Babies born with lactose intolerance (congenital lactase deficiency) don’t put on weight as they should and will show signs of not getting enough nutrients. They will need to be fed a special diet from birth.

Causes of lactose intolerance

Lactose intolerance develops when you have a shortage of the enzyme lactase in your body. There are three main causes of lactose intolerance.

  • Primary lactase deficiency. This is a gradual reduction in the amount of lactase your body produces as you get older.
  • Congenital lactase deficiency. This means you have inherited a rare disorder in which you produce little or no lactase from birth.
  • Secondary lactose intolerance. This is when a separate condition such as gastroenteritis damages the lining of your bowel and reduces the amount of lactase you produce. It's usually only temporary and your symptoms should disappear several weeks after the condition goes away.

Diagnosis of lactose intolerance

Your GP will ask about your symptoms and examine you. He or she may ask you to keep a diary of your symptoms and what you consume on a day-to-day basis. This will help your GP to look for any links between your symptoms and what you eat and drink.

To confirm whether you have lactose intolerance, your GP may suggest you completely remove dairy products from your diet for a trial period of two or three weeks. If your symptoms are relieved during this time, it's likely that you have lactose intolerance.

If you think your child may have the symptoms of lactose intolerance, your GP may ask for a sample of his or her faeces (stool sample), which will be sent away for testing. This is called a stool acidity test.

Having specific tests to diagnose lactose intolerance is uncommon. If there is uncertainty about your diagnosis, you may be referred to a specialist doctor for further tests. He or she may ask you to have one or more of the following.

  • Blood test. Your doctor will take a blood sample after you’ve consumed lactose by mouth to measure your blood sugar (glucose) level. If your blood sugar level increases by only a small amount or doesn't increase at all, this suggests that your body hasn’t digested or absorbed the lactose into your bloodstream and is a sign that you may have lactose intolerance.
  • Hydrogen breath test. After you’ve drunk some milk, you doctor will measure the level of hydrogen in your breath. If there is a large amount of hydrogen in your breath, this may be a sign that you have lactose intolerance. This is because hydrogen is formed when bacteria in your bowel act on undigested lactose.
  • Biopsy. You may need to have a biopsy (a small sample of tissue) taken from the lining of your small bowel. This is done using a narrow, flexible tube-like instrument called an endoscope. The sample will be sent to a laboratory to be tested for lactase.

Treatment of lactose intolerance

There isn’t a cure for lactose intolerance, but you can control your symptoms by reducing the amount of lactose in your diet.

Most people who have lactose intolerance can have a small amount of milk (around 200ml) with a meal, without reacting to it. You could try drinking small amounts of milk to find out how much you can tolerate without having any symptoms.

You should try to include cheese, yoghurt and low lactose milk in your diet as dairy products are a good source of calcium. You can buy milk and other products that contain a reduced amount of lactose from supermarkets. Hard cheeses, such as cheddar, edam and parmesan only contain a small amount of lactose, so you will usually be able to eat these without having any symptoms. You may also find that you're able to eat yoghurt without any problems. This is thought to be partly because there is an enzyme similar to lactase found in the bacteria that is used to produce yoghurt.

You can also buy lactase preparations, either as a liquid that you add to milk, or as tablets that you take before consuming something containing lactose.

If you're very sensitive to lactose, remember that it's often found in some processed food products such as bread, meats and some drinks, such as lagers and beers. Check the labels for ingredients.

If you're unable to eat any dairy foods, you may not be getting enough calcium in your diet. Non-dairy foods that contain calcium include green leafy vegetables, soya beans, tofu and nuts. Talk to your GP about your diet and he or she may refer you to a dietician for help and support.


For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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  • Produced by Krysta Munford, Bupa Health Information Team, February 2012.

Nutrition and dietetics

Bupa's private Cromwell Hospital has a team of registered dieticians that can offer tailored dietary advice based on specific medical conditions.