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Lactose intolerance

Key points

  • Lactose intolerance means your bowel can’t break down the sugar found in milk and dairy products.
  • Some of the symptoms of lactose intolerance include feeling bloated, pain in your tummy (abdomen) and diarrhoea.
  • Lactose intolerance can’t be cured, but you can control your symptoms by cutting down the amount of lactose in your diet.

Lactose intolerance means your body can’t break down lactose (a sugar mainly found in milk).

About lactose intolerance

Lactose is a sugar found in milk and other dairy products. An enzyme (a type of chemical) called lactase, which is produced by your small bowel, breaks lactose down into two simpler sugars (glucose and galactose). Once lactose has been broken down, it's absorbed from your bowel into your bloodstream.

If your body doesn’t make enough lactase, you may develop symptoms of lactose intolerance. Lactose intolerance usually affects older children and adults because the level of lactase starts to decrease naturally as you get older.

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 can occur after you’ve eaten or drunk something that contains lactose. Symptoms of lactose intolerance may include:

  • feeling bloated
  • pain or cramps in your tummy (abdomen)
  • diarrhoea
  • wind
  • feeling sick

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

Complications of lactose intolerance

If you have lactose intolerance, you can control your symptoms by reducing the amount of lactose in your diet. However, the lack of dairy products in your diet will mean you need to get vitamin D and the mineral calcium, from other sources. If you don’t get enough calcium in your diet, your bones may become weak and you may develop a condition known as osteopenia.

Babies born with the rare but more severe form of lactose intolerance may not grow as they should if they don’t receive the right nutrients. They will need to be fed a lactose-free formula from birth.

Causes of lactose intolerance

Lactase deficiency is when your body doesn’t produce enough lactase, which can lead to symptoms of lactose intolerance.

There are three main types of lactase deficiency.

  • Primary lactase deficiency is caused by an inherited faulty gene that runs in families. It can occur at different ages.
  • Secondary lactase deficiency is when the lining of your bowel becomes damaged by a separate condition such as gastroenteritis. This may reduce the amount of lactase that your body makes. Secondary lactase deficiency is usually temporary and gets better once you have recovered from the condition that caused it. 
  • Congenital lactase deficiency is a condition that also runs in families, but it’s very rare. It can cause you to produce little or no lactase from birth, and if left untreated, it can lead to serious complications. To find out more about congenital lactase deficiency see our FAQ.

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 eat and drink on a day-to-day basis. This will help your GP to look for any links between your symptoms and your diet.

Your GP may suggest you completely remove foods and drinks containing lactose from your diet for a trial period of two weeks. If your symptoms get better during this time, but come back when you start having lactose again, it's likely that you have lactose intolerance.

If you think your child may have symptoms of lactose intolerance, your GP may ask for a sample of his or her faeces (stool sample). This will be sent away for testing to check if your child’s body is absorbing lactose.

Having specific tests to diagnose if you have lactose intolerance is uncommon. However, if there is uncertainty about your diagnosis, your GP may refer you to have one or more of the following tests.

  • Hydrogen breathe test. After you’ve drunk some milk, the level of hydrogen (a type of gas) in your breath will be measured. Lactose intolerance can cause the bacteria in your bowel to produce more hydrogen than normal. Therefore, if there’s a large amount of hydrogen in your breath, this may be a sign that you have lactose intolerance. 
  • A lactose tolerance blood test. Your doctor will take a blood sample after you’ve had some lactose by mouth to measure your blood sugar (glucose) level. If your blood sugar level increases by a small amount or not at all, this suggests that your body hasn’t digested or absorbed the lactose. This is a sign that you may have lactose intolerance.
  • Biopsy. If your diagnosis is uncertain 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. Milk and dairy products are the main sources of lactose and cutting down how much of these products you have may help your symptoms. We’ve put together some tips to help you with this.

  • Hard cheeses, such as Cheddar, Edam and Parmesan, only contain a small amount of lactose. Therefore, you may be able to eat these without having any symptoms.
  • You may also find that you can eat yoghurt without any problems. This is thought to be partly because of the effects of the bacteria that are used to produce yoghurt.
  • You can also buy lactase preparations to take if you eat foods containing lactose.
  • There may be lactose in some foods that you don’t expect to contain it, for example bread, cakes, cereals, margarine and some ready meals. Check the ingredients as the label should say whether a product contains lactose.
  • You may be able to have some milk (about 200ml – a small glass) without reacting to it. You could try having small amounts of milk to find out how much you can drink without getting any symptoms.
  • You can buy milk and other products that contain a reduced amount of lactose. It’s important to remember that milk from goats and sheep contains lactose and so these aren’t suitable alternatives to cow’s milk.
  • Some medicines may contain lactose. Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

If you can’t 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 if you have any questions. He or she may refer you to a dietitian for help and support. Your GP may also recommend that you take calcium and vitamin D supplements.

Reviewed by Kuljeet Battoo, Bupa Health Information Team, July 2014.

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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.

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