Lactose intolerance is a common digestive problem where the body is unable to digest lactose, a type of sugar mainly found in milk and dairy products.
Symptoms of lactose intolerance usually develop within a few hours of consuming food or drink that contains lactose. They may include:
The severity of your symptoms and when they appear depends on the amount of lactose you've consumed.
Some people may still be able to drink a small glass of milk without triggering any symptoms, while others may not even be able to have milk in their tea or coffee.
When to seek medical advice
The symptoms of lactose intolerance can be similar to several other conditions, so it's important to see your doctor for a diagnosis before removing milk and dairy products from your diet.
For example, the symptoms above can also be caused by:
- irritable bowel syndrome (IBS) – a long-term disorder that affects the digestive system
- milk protein intolerance – an adverse reaction to the protein in milk from cows (not the same as a milk allergy )
If your doctor thinks you have lactose intolerance, they may suggest avoiding foods and drinks containing lactose for two weeks to see if your symptoms improve.
Read more about diagnosing lactose intolerance .
What causes lactose intolerance?
The body digests lactose using a substance called lactase. This breaks down lactose into two sugars called glucose and galactose, which can be easily absorbed into the bloodstream.
People with lactose intolerance don't produce enough lactase, so lactose stays in the digestive system where it's fermented by bacteria. This leads to the production of various gases, which cause the symptoms associated with lactose intolerance.
Depending on the underlying reason why the body isn't producing enough lactase, lactose intolerance may be temporary or permanent. Most cases that develop in adults are inherited and tend to be lifelong, but cases in young children are often caused by an infection in the digestive system and may only last for a few weeks.
Read more about the causes of lactose intolerance .
In the UK, lactose intolerance is more common in people of Asian or African-Caribbean descent.
Lactose intolerance can develop at any age. Many cases first develop in people aged 20 to 40, although babies and young children can also be affected.
Is it an allergy?
Lactose intolerance isn't the same as a milk or dairy allergy. Food allergies are caused by your immune system reacting to a certain type of food. This causes symptoms such as a rash, wheezing and itching.
If you're allergic to something, even a tiny particle can be enough to trigger a reaction, while most people with lactose intolerance can still consume small amounts of lactose without experiencing any problems (although this varies from person to person).
Treating lactose intolerance
There's no cure for lactose intolerance, but limiting your intake of food and drink containing lactose usually helps to control the symptoms.
Depending on what dairy products you're able to eat, you may also require additional calcium and vitamin D supplements to keep your bones strong and healthy. In some cases, your doctor may refer you to a dietitian for further advice.
In addition to dietary changes, lactase substitutes may also be helpful. These are drops or tablets you can take with your meals or drinks to improve your digestion of lactose.
Read more about treating lactose intolerance .
Complications of lactose intolerance
Milk and other dairy products contain calcium, protein and vitamins such as A, B12 and D. Lactose also helps your body absorb a number of other minerals, such as magnesium and zinc. These vitamins and minerals are important for the development of strong, healthy bones.
If you're lactose intolerant, getting the right amount of important vitamins and minerals can prove difficult. This may lead to unhealthy weight loss and put you at increased risk of developing the following conditions:
- Osteopenia – where you have a very low bone-mineral density. If osteopenia is not treated, it can develop into osteoporosis.
- Osteoporosis – where your bones become thin and weak. If you have osteoporosis, your risk of getting fractures and broken bones is increased.
- Malnutrition – when the food you eat doesn't give you the nutrients essential for a healthy functioning body. If you're malnourished, wounds can take longer to heal and you may start to feel tired or depressed.
If you're concerned that dietary restrictions are putting you at risk of complications, you may find it helpful to consult a dietitian. They can advise you on your diet and whether you require food supplements.
Your doctor should be able to refer you to a dietitian. Alternatively, you can contact a private dietician. The British Dietetic Association has information on how to find a private dietitian.
Causes of lactose intolerance
Lactose intolerance is usually the result of your body not producing enough lactase.
Lactase is an enzyme (a protein that causes a chemical reaction to occur) normally produced in your small intestine that's used to digest lactose.
If you have a lactase deficiency, it means your body doesn't produce enough lactase.
After eating or drinking something containing lactose, it passes down your oesophagus (gullet) into your stomach, where it's digested. The digested food then passes into your small intestine.
The lactase in your small intestine should break lactose down into glucose and galactose (other types of sugar), which are then absorbed into your bloodstream. If there isn't enough lactase, the unabsorbed lactose moves through your digestive system to your colon (large intestine).
Bacteria in the colon ferment (break down) the lactose, producing fatty acids and gases such as carbon dioxide, hydrogen and methane. The breakdown of the lactose in the colon, and the resulting acids and gases that are produced, cause the symptoms of lactose intolerance such as flatulence and bloating.
Types of lactase deficiency
The main types of lactase deficiency are outlined below.
Primary lactase deficiency
Primary lactase deficiency is the most common cause of lactose intolerance worldwide. This type of lactase deficiency is caused by an inherited genetic fault that runs in families.
Primary lactase deficiency develops when your lactase production decreases as your diet becomes less reliant on milk and dairy products. This is usually after the age of two, when breastfeeding or bottle-feeding has stopped, although the symptoms may not be noticeable until adulthood.
Secondary lactase deficiency
Secondary lactase deficiency is a shortage of lactase caused by a problem in your small intestine. It can occur at any age, and may be the result of another condition, surgery to your small intestine, or taking certain medication.
Secondary lactase deficiency is the most common cause of lactose intolerance in the UK, particularly in babies and young children.
Possible causes of secondary lactase deficiency include:
- gastroenteritis – an infection of the stomach and intestines
- coeliac disease – a bowel condition caused by an adverse reaction to a protein called gluten
- Crohn's disease – a long-term condition that causes inflammation of the lining of the digestive system
- ulcerative colitis – a long-term condition that affects the large intestine
- chemotherapy – a cancer treatment
- long courses of antibiotics
The decrease in the production of lactase in secondary lactase deficiency is sometimes only temporary, but it may be permanent if it's caused by a long-term condition.
It's also possible to develop secondary lactase deficiency later in life, even without another condition to trigger it. This is because your body's production of lactase naturally reduces as you get older.
Congenital lactase deficiency
Congenital lactase deficiency is a rare condition that runs in families and is found in newborn babies.
It's caused by an inherited genetic fault that means affected babies produce very little or no lactase.
The genetic mutation responsible for congenital lactase deficiency is passed on in an autosomal recessive inheritance pattern. This means both parents must have a copy of the faulty gene to pass on the condition.
Read more about genetic inheritance .
Developmental lactase deficiency
Some babies born prematurely (before the 37th week of pregnancy) have a temporary lactose intolerance because their small intestine wasn't fully developed by the time they were born.
This is known as developmental lactase deficiency and it usually improves as affected babies get older.
Diagnosing lactose intolerance
It's important to visit your doctor if you think you or your child may have lactose intolerance, as the symptoms can be similar to other conditions.
Before seeing your doctor, keep a diary of what you eat and drink, and what symptoms you experience. Tell your doctor if you notice any patterns, or if there are any foods you seem particularly sensitive to.
Your doctor may suggest trying to remove lactose from your diet for two weeks to see if it helps to relieve your symptoms. This will provide further evidence of whether you're lactose intolerant.
Other tests aren't usually needed, but your doctor may sometimes suggest further tests to:
- help confirm the diagnosis
- find out how much lactase (the enzyme used to digest lactose) your body is producing
- try to determine what might be causing your lactose intolerance
Some of the main tests that may be used are described below.
Hydrogen breath test
A hydrogen breath test is a simple way of determining if you may be lactose intolerant.
You'll be asked to avoid eating or drinking during the night before the test. When you arrive for the test, you'll be asked to blow up a balloon-like bag. This sample of your breath will be tested to find out how much hydrogen is present, measured in parts per million (ppm).
You'll then be given a drink of lactose solution and your breath will be tested every 15 minutes over the next few hours to see if the level of hydrogen changes.
If your breath contains a large amount of hydrogen (more than 20ppm above your baseline) after consuming the lactose solution, it's likely that you're lactose intolerant. This is because lactose intolerance can cause the bacteria in the colon (large intestine) to produce more hydrogen than normal.
Lactose tolerance test
In a lactose tolerance test, you'll be given a drink of lactose solution and a blood sample will be taken from your arm using a needle. The blood will be tested to see how much glucose (blood sugar) it contains.
If you're lactose intolerant, your blood sugar levels will either rise slowly, or not at all. This is because your body is unable to break down the lactose into glucose.
Milk tolerance test
In a milk tolerance test, you'll be given a glass of milk (about 500ml) and your blood sugar levels will be tested. If your blood sugar levels don't rise after drinking the milk, you may be lactose intolerant.
Small bowel biopsy
A small bowel biopsy is rarely used to diagnose lactose intolerance. However, it may be carried out to see if your symptoms are being caused by another condition, such as coeliac disease .
In a small bowel biopsy, a sample of your small intestinal lining is taken using an endoscope (a thin, flexible tube with a light and a tiny cutting tool at the end) that's passed down your throat. This will be carried out under local anaesthetic , so it won't hurt.
The sample of intestinal lining will be tested to see how much lactase it contains. If it only contains a small amount of lactase, it's likely you're lactose intolerant. The sample can also be examined to look for signs of possible underlying conditions such as coeliac disease.
Treating lactose intolerance
There's no cure for lactose intolerance, but most people are able to control their symptoms by making changes to their diet.
Some cases of lactose intolerance, such as those caused by gastroenteritis , are only temporary and will improve within a few days or weeks. Other cases, such as those caused by an inherited genetic fault or a long-term underlying condition, are likely to be lifelong.
Changing your diet
In most cases, cutting down on or avoiding sources of lactose and replacing them with lactose-free alternatives is enough to control the symptoms of lactose intolerance.
The exact changes you need to make to your diet depend on how sensitive you are to lactose. Some people are able to tolerate some lactose in their diet without any problems, whereas others experience symptoms after consuming food containing only a tiny amount of lactose.
If you decide to experiment with what you can and can't eat, make sure to introduce new foods gradually, rather than all at once. This will help you to get used to any foods you might be sensitive to and identify any that cause problems.
Eating fewer products containing lactose, or avoiding them completely, can mean you miss out on certain vitamins and minerals in your diet and increase your risk of complications. You'll also need to make sure you're getting enough nutrition from either lacto-free foods or dietary supplements.
If you or your child are extremely sensitive to lactose, talk to your doctor about your diet.
Milk products are rich in calcium needed for healthy bones so you may need to have regular bone density checks.
You may be referred to a dietitian (an expert in diet and nutrition) who can advise you about what foods should be included in your, or your child's, diet.
Sources of lactose
Some of the main sources of lactose you may need to cut down on or avoid if you're lactose intolerant are described below.
A major source of lactose is milk, including cow's milk, goat's milk and sheep's milk. Depending on how mild or severe your lactose intolerance is, you may need to change the amount of milk in your diet.
- you may be able to have milk in your tea or coffee, but not on your cereal
- some products containing milk, such as milk chocolate, may still be acceptable in small quantities
- you may find that drinking milk as part of a meal, rather than on its own, improves how the lactose is absorbed
If even a small amount of milk triggers your symptoms, there are some alternatives you can try, such as soya or rice milk (see below).
Other dairy products made from milk – such as cream, cheese, yoghurt, ice cream and butter – also contain lactose and may need to be avoided if you're lactose intolerant.
But the level of lactose in these products varies and is sometimes quite low, so you may still be able to have some of them without experiencing any problems.
It's worth experimenting with different foods to find out if there are any dairy products you can eat because they're a good source of essential nutrients such as calcium .
Other foods and drinks
As well as milk and dairy products, there are other foods and drinks that can sometimes contain lactose.
- salad cream, salad dressing and mayonnaise
- boiled sweets
- some types of bread and other baked goods
- some breakfast cereals
- packets of mixes to make pancakes and biscuits
- packets of instant potatoes and instant soup
- some processed meats, such as sliced ham
Check the ingredients of all food and drink products carefully, because milk or lactose are often hidden ingredients.
The lactose found in some foods won't necessarily be listed separately on the food label, so you need to check the ingredients list for milk, whey, curds and milk products such as cheese, butter and cream.
Some ingredients may sound like they contain lactose when they don't, such as lactic acid, sodium lactate and cocoa butter. These ingredients don't need to be avoided if you're lactose intolerant.
Some prescription medicines, over-the-counter medicines and complementary medicines may contain a small amount of lactose. While this isn't usually enough to trigger the symptoms of lactose intolerance in most people, it may cause problems if your intolerance is severe or you're taking several different medicines.
If you need to start taking a new medication, check with your doctor or pharmacist in case it contains lactose.
Lactose-free foods and drinks
There are a number of alternative foods and drinks available in supermarkets to replace the milk and dairy products you need to avoid.
Food and drinks that don't usually contain lactose include:
- soya milks, yoghurts and some cheeses
- milks made from rice, oats, almonds, hazelnuts, coconut, quinoa, and potato
- foods which carry the 'dairy-free' or 'suitable for vegans' signs
- carob bars
You can also buy cow's milk containing additional lactase (the enzyme used to digest lactose). This means you still get the nutritional benefits of the milk, but you're less likely to experience any symptoms after consuming it.
Getting enough calcium
If you're unable to eat most dairy products, you may not be getting enough calcium in your daily diet. Calcium has several important functions, including:
- helping build strong bones and teeth
- regulating muscle contractions (including heartbeat)
- ensuring blood clots normally
Therefore, it's a good idea to choose lactose-free products with added calcium and ensure your diet contains alternative sources of calcium, such as:
- green leafy vegetables, such as spinach, kale, broccoli, cabbage and okra
- soya beans
- bread and anything made with fortified flour
- fish containing edible bones (for example, sardines, salmon, and pilchards)
You can also buy combined calcium and vitamin D supplements from most pharmacists to help maintain good bone health.
It's important to check with your doctor or dietitian whether you should be taking supplements, however, as taking excessively high levels of calcium can cause side effects.
In addition to dietary changes, you may also find it useful to take liquid drops, tablets or capsules that contain lactase substitutes. These are available from most health foods shops.
Lactase substitutes replace the lactase your small intestine isn't producing, which can reduce your symptoms by helping your body break down any lactose in your diet more easily.
Lactase substitutes can either be added to milk or taken just before eating a meal containing lactose.
Lactose intolerance in children
If your child is lactose intolerant, they may be able to consume small amounts of lactose without experiencing symptoms. This is quite safe, but you may need to experiment to find out how much they can comfortably eat or drink.
If your child is unable to tolerate any lactose, your doctor may refer you to a dietitian for nutritional advice because it's important for young children to have certain nutrients in their diet to ensure healthy growth and development.
In general, the same rules about foods to try or to avoid are similar for children and adults (see above).
For babies with lactose intolerance, lactose-free formula milk is available to buy from pharmacies and supermarkets. However, soya formula isn't recommended for children under six months because it contains hormones that may interfere with your baby's future physical and sexual development.
Breastfed babies may benefit from lactase substitute drops to help their bodies digest the lactose in breast milk.
For many children, lactose intolerance is only temporary and will improve after a few weeks. After this point it's safe to gradually reintroduce milk and dairy products into their diet.