Lactose intolerance

Expert reviewer Dr Adrian Raby, General Practitioner and Clinical Lecturer
Next review due February 2020

Lactose intolerance means your digestive system can’t break down lactose (a sugar mainly found in milk). This may give you unpleasant symptoms such as bloating, diarrhoea and tummy cramps.

It’s quite a common problem, and unfortunately there’s no treatment that will cure it. However, you can usually control your symptoms by being careful what you eat and drink.

Young woman eating pizza

About lactose intolerance

Lactose is a sugar found in milk and other dairy products. Your small bowel makes an enzyme called lactase. This breaks lactose down into two simpler sugars – glucose and galactose. Your body can then absorb these simpler sugars into your bloodstream.

If your bowel doesn’t make enough lactase, you may develop symptoms of lactose intolerance after eating or drinking milk and other dairy products. The lactose in your food can’t be absorbed so stays in your bowel. The bacteria in your bowel then break it down to form gas and other by-products. The lactose also makes your bowel contents more liquid.

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 such a big part of the usual adult diet, such as South America, Africa and Asia.

Symptoms of lactose intolerance

The symptoms of lactose intolerance usually occur between 20 minutes and 2 hours after you’ve eaten or drunk something that contains lactose. Symptoms may include:

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

Your symptoms may range from mild to severe. How bad they are may depend on how much lactose you’ve consumed. It may also depend on how high your own individual tolerance is.

These symptoms may be caused by problems other than lactose intolerance, including gastroenteritis, irritable bowel syndrome and coeliac disease. If you have any of these symptoms for more than a few days contact your GP for advice.

Diagnosis of lactose intolerance

Your GP will ask about your symptoms and may examine you. They may ask you to keep a diary of your symptoms and what you eat and drink on a day-to-day basis. This is perhaps something you could do anyway before your appointment and take with you. 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.

Other tests aren’t usually needed to diagnose lactose intolerance.

If your GP isn’t sure about the diagnosis they may refer you to a specialist, who may recommend you have a hydrogen breath test. Lactose intolerance can cause the bacteria in your bowel to produce more hydrogen than normal. So if there’s a lot of hydrogen in your breath, this may be a sign that you have lactose intolerance. For this test you’ll be given a drink that contains lactose. Then you’ll be asked to breathe into a balloon-type container. This measures how much hydrogen is in your breath.

If your diagnosis is uncertain and your symptoms keep on going your doctor may recommend a biopsy. This is where a doctor takes a small sample of tissue 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 the enzyme lactase.

If you’re offered any of these tests, you’ll be given information about how to prepare and what will happen during the test. If you have any questions you can ask the healthcare staff carrying out the test.

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Treatment of lactose intolerance

There isn’t a cure for lactose intolerance. If it’s caused by another illness it should go away of its own accord (see our causes section below). If not, you can usually control your symptoms by making changes to your diet. Some people may only need to cut down the amount of lactose they eat and drink, others may need to avoid it altogether. Milk and dairy products are the main sources of lactose.

If you have lactose intolerance, here are some tips to help you reduce your symptoms.

  • Hard cheeses, such as Cheddar, Edam and Parmesan, only contain a small amount of lactose. So you may be able to eat these without having any symptoms.
  • You may also find that you can eat yoghurt without any problems. This may be partly because of the effects of the bacteria that are used to produce yoghurt.
  • You can buy preparations of the enzyme lactase to take. These may help you if you eat foods containing lactose.
  • Watch out for lactose in some foods that you don’t expect to contain it, such as bread, cereals and some ready meals. Check the ingredients – the label should say whether a product contains lactose.
  • You may find you can tolerate milk if you have it with meals, rather than on its own.
  • 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 read the patient information leaflet that comes with your medicine and ask your pharmacist if you have any queries.

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 sardines. Talk to your GP about your diet if you’re concerned. They may refer you to a dietitian for help and support. Your GP may also recommend that you take calcium and vitamin D supplements.

You can get more tips and information about diet and lactose intolerance from the organisations listed in our section below – other helpful websites.

Causes of lactose intolerance

Lactase deficiency is when your small bowel doesn’t produce enough of the enzyme lactase. This means that you can’t absorb lactose from your food. It stays in your bowel and is broken down by bacteria there. This can lead to symptoms of lactose intolerance.

There are four main types of lactase deficiency.

  • Primary lactase deficiency is the most common cause of lactose intolerance. It happens when the amount of lactase in your bowel falls over time, usually from about the age of two. Whether your levels of lactase decline or not over time is linked to your genetic make-up, so runs in families.
  • Secondary lactase deficiency is when the lining of your bowel becomes damaged by a separate condition such as gastroenteritis. It’s usually temporary and gets better once you have recovered from the condition that caused it.
  • Congenital lactase deficiency – where a baby is born with the condition – also runs in families, but it’s very rare. To find out more about congenital lactase deficiency see our FAQ below.
  • Developmental lactase deficiency. This can happen in babies who are born prematurely. This usually only lasts for a short time after the baby is born.

Complications of lactose intolerance

If you have lactose intolerance, you can usually control your symptoms by reducing the amount of lactose in your diet. However, reducing milk and other dairy products in your diet may make it hard for you to get enough calcium and vitamin D. If you don’t get enough calcium in your diet this may eventually affect your bones. They may become weak and less dense, making them more likely to fracture (osteoporosis).

See our section on treatment of lactose intolerance above for tips on how to make safe changes to your diet. And speak with your GP if you’re concerned about your diet. They may recommend that you take calcium and vitamin D supplements. They may also be able to refer you to a dietitian for further advice.

Frequently asked questions

  • It’s possible, but it’s very rare for babies to be born with lactose intolerance.

    More information

    Some babies may be born without the ability to produce lactase, but it’s very rare. The condition is known as congenital lactase deficiency. If your baby has congenital lactase deficiency, they may develop diarrhoea when they drink milk (breast milk or formula milk) that contains lactose.

    The only treatment for congenital lactase deficiency is to remove lactose from your baby’s diet from birth. Your GP will refer you to a specialist to confirm the diagnosis and arrange for you and your baby to see a dietitian. A dietitian can help ensure your baby’s diet is lactose-free. Your baby will probably need to take calcium and vitamin D supplements.

    If your baby seems to be having problems with feeding or is having symptoms such as diarrhoea, contact your GP or health visitor. Don’t stop breastfeeding or giving your baby milk without talking to your GP first.

  • No. If you or your child have lactose intolerance, it means your body can’t break down a sugar in milk called lactose. If your child has a milk allergy, it means they’re allergic to some of the proteins found in milk. Lactose intolerance tends to affect older children and adults, whereas milk allergy is much more common in babies and young children.

    More information

    Lactose intolerance and milk allergy can be confused because the symptoms of both occur after eating or drinking dairy products.

    If you or your child have lactose intolerance, it means the body doesn’t have enough lactase. This is an enzyme that your body needs to break down the lactose in milk. If lactose isn’t broken down, it can cause symptoms, such as diarrhoea and bloating.

    If your child has an allergy to milk, their immune system mistakes some of the proteins found in milk as harmful. This leads to an allergic reaction. Children usually start having symptoms in their first few months, and almost always by the end of the first year. Most children grow out of milk allergy by the age of five so it’s unusual for older children and adults to have it.

    The symptoms of milk allergy usually begin within a week of starting your baby on cow’s milk, although they may be delayed for many weeks. Symptoms are often mild, but can be severe. They may include vomiting, diarrhoea and a skin rash.

    Very rarely, a baby with milk allergy can have a severe reaction called anaphylaxis. They may have breathing difficulties and go floppy – if so, they will need immediate medical attention.

    If you or your child feel unwell after drinking milk or eating dairy products, contact your GP. Don’t cut milk or dairy products out of your own or your child’s diet without talking to your GP first. Babies with a cow’s milk allergy may be given a special formula. Goat’s milk and sheep’s milk are not suitable alternatives to cow’s milk for those with cow’s milk allergy or lactose intolerance.

  • Yes, because soya milk doesn’t contain lactose. Although there isn’t a cure for lactose intolerance, you can control your symptoms by reducing the amount of lactose in your diet. One way of doing this is by drinking soya milk instead of cow, sheep or goat milk, as it doesn’t contain any lactose.

    It’s important not to completely cut out dairy products from your diet unless you’re very sensitive to lactose. This is because these foods are an important source of calcium and vitamin D. Calcium is important to keep your bones healthy. If you want to drink soya milk as an alternative, it’s a good idea to choose a product that has added calcium. See our section on treatment of lactose intolerance above.

    If you need more information, ask your dietitian or GP for advice. The organisations listed below in our section ‘other helpful websites’ also have more information on diet and lactose intolerance.

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Related information

    • Lactase deficiency. BMJ Best Practice., last updated 8 February 2016
    • Lactose intolerance. Medscape., updated 14 July 2015
    • Lactose intolerance. PatientPlus., last checked 2 December 2016
    • Food allergy and food intolerance. PatientPlus., last checked 8 May 2015
    • Lactose intolerance. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), 2014.
    • Lactose intolerance. British Nutrition Foundation., last reviewed September 2009
    • Milk allergy. Allergy UK., last updated January 2015
    • Does my child have cow’s milk allergy? Allergy UK., last updated October 2013
    • Calcium: Food fact sheet. BDA, The Association of UK Dietitians., 2014
    • Soya, food and health: Food fact sheet. BDA, The Association of UK Dietitians, 2014.
    • Luyt D, Ball H, Makwana N, et al. BSACI guideline for the diagnosis and management of cow’s milk allergy. Clin Exp Allergy 2014; 44(5):642–72. doi:10.1111/cea.12302.
  • Reviewed by Dr Kristina Routh, Freelance Health Editor, February 2017
    Expert reviewer Dr Adrian Raby, General Practitioner and Clinical Lecturer
    Next review due February 2020

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