Lactose intolerance
Introduction
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 include
Read more about the symptoms of lactose intolerance.
An intolerance is not the same as a food allergy. 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 with no ill-effects.
The amount of lactose a person can consume can change, sometimes sharply, from person to person.
What causes lactose intolerance?
The body digests lactose by using an enzyme called lactase to break down lactose into two simpler sugars called glucose and galactose, which can then be easily absorbed into the bloodstream. Enzymes are proteins that cause chemical reactions to occur.
In cases of lactose intolerance, the body does not produce enough of the lactase enzyme so lactose stays in the digestive system, where it is fermented by bacteria (in the same way that yeast is fermented to produce beer). It’s this fermentation process that causes the symptoms associated with lactose intolerance.
Levels of lactase often fall as people grow older and some health conditions can also reduce the production of lactase.
Read more about the causes of lactose intolerance.
Diagnosing lactose intolerance
If you suspect that you may be lactose intolerant it is important to get a diagnosis confirmed (or ruled out) by a doctor.
Many experts are concerned that people wrongly ‘self-diagnose’ themselves as lactose intolerant and miss out on the nutrients that dairy product provide.
Similarly, many parents wrongly assume they have passed the condition on to their children, where this may not actually be the case.
Lactose intolerance can be diagnosed with a breath and /or blood test that can assess how the body reacts to lactose.
Read more about the diagnosis of lactose intolerance.
Treating lactose intolerance
Limiting your intake of food and drink containing lactose is the main treatment for lactose intolerance.
Depending on a person’s levels of intolerance, they may also require additional calcium and vitamin D supplements to keep the bones strong and healthy.
Advice from a dietitian may sometimes be helpful in determining the best diet for a person.
Lactase substitutes are also available. These are drops that you can add to your meals or drinks to improve your digestion of lactose.
Read more about treating lactose intolerance.
Who is affected
Levels of lactose intolerance can differ in different ethnic groups. For example, it is thought that only 1 in 50 people of Swedish descent have some degree of lactose intolerance whereas almost all people of Chinese descent have the condition.
In the UK, it’s more common in people of Asian or African-Carribean descent.
Most cases first develop in people aged 20-40, although in rare cases the intolerance can be present at birth. Both sexes are equally affected by lactose intolerance.
Outlook
It can sometimes be difficult at first for a person to assess how much lactose they can eat without ill effects. But usually, with time, a person learns to ‘judge their own limits’ and work out what they can eat and drink without it causing symptoms.
Complications such as osteoporosis that arise from a lack of nutrients in the diet can usually be avoided with advice from a GP and/or dietitian on whether food supplements are required.
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Symptoms
The symptoms of lactose intolerance will occur after consuming food or drink that contains lactose, such as dairy products.
The main symptoms include:
- flatulence (wind)
- diarrhoea three or more times a day
- bloated stomach
- stomach pains
- stomach rumbling
- feeling sick
- stomach cramps
The severity of your symptoms and when you begin to experience them will depend on the amount of lactose that you have consumed.
The amount of lactose that it takes to cause your symptoms will vary from person to person. For example, 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.
Conditions that cause similar symptoms
The symptoms of lactose intolerance can be similar to those of other conditions, such as irritable bowel syndrome (IBS) or milk protein intolerance. IBS is a chronic (long-term) disorder that affects the digestive system.
Milk protein intolerance is an adverse reaction to the protein in milk from cows, but it does not involve the immune system (and so is not the same as milk allergy). Due to the similarities, these three conditions can sometimes be confused.
This is why it is always important to get a medical diagnosis if you think that you or your child may have lactose intolerance.
Read more about diagnosing lactose intolerance.
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Causes
Lactose intolerance is usually the result of a lactase deficiency. Lactase is an enzyme (protein that causes a chemical reaction to occur) that is normally produced in your small intestine.
If you have a lactase deficiency, it means that your body does not produce enough lactase.
Digesting lactose
After eating or drinking something that contains lactose, it passes down your oesophagus (gullet) and into your stomach, where it is digested. The digested food then passes into your small intestine.
The lactase in your small intestine should break down the lactose into glucose and galactose (another type of sugar), which are then absorbed into your bloodstream. If there is not enough lactase, the intact, unabsorbed lactose moves through your digestive system to your colon (your 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.
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. This type of lactase deficiency is genetically inherited (it runs in families).
Primary lactase deficiency develops when your lactase production decreases as a result of your diet being 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 or surgery to your small intestine, or it can be caused by some medications.
Possible causes of secondary lactase deficiency include:
- coeliac disease, a bowel condition that is caused by an intolerance to a protein called gluten
- gastroenteritis, an infection of the stomach and intestines
- Crohn's disease, a chronic (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 treatment for cancer
- long courses of antibiotics
Certain conditions and treatments can cause a decrease in the production of lactase. Sometimes the deficiency is temporary, but if it is caused by a long-term condition it may be permanent.
It is 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 is caused by a genetic mutation (a gene change), which stops one or more processes of the body from working in the right way. Read more about genes and how they can affect our health.
The genetic mutation is passed through families in what is known as autosomal recessive inheritance.
Familial lactase deficiency
Familial lactase deficiency is similar to congenital lactase deficiency, and is also found in newborn babies. However, with this type of lactase deficiency, your body is able to produce a substantial amount of lactase, but the enzyme does not work and cannot break down the lactose.
As with congenital lactase deficiency, the genetic mutation responsible for the production of lactase is passed on in autosomal recessive inheritance.
Lactose intolerance and evolution
It is thought that rates of lactose intolerance differ so widely among different ethnic groups because of evolution.
In cultures where there was ready access to milk or similar dairy products, such as Europe, being able to digest lactose improved your chances of surviving to adulthood and having children. So over time, people without the lactose intolerance gene were more likely to reproduce than people with it.
But in other cultures where there was no ready access to milk, such as Africa or China, there was no significant benefit in being able to digest lactose. So the same evolutionary forces did not apply.
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Diagnosis
You should visit your GP if you think you have lactose intolerance. Before visiting your GP, keep a diary of what you eat and drink, and what symptoms you experience. Tell your GP if you notice any patterns, or if there are any foods that you seem particularly sensitive to.
Your GP may suggest that you try removing lactose from your diet for two weeks to see if it helps to relieve your symptoms. This will provide further evidence that you are lactose intolerant.
Further testing
Your GP may suggest further tests to find out how much (if any) lactase your body is producing and what might be causing your lactose intolerance.
Hydrogen breath test
A hydrogen breath test is a simple and useful test.
You will be given a drink of lactose solution after you have fasted overnight. The concentration of hydrogen is measured in the air that you breathe out. It is measured in parts per million (ppm).
If after about an hour your breath contains a large amount of hydrogen (more than 20 ppm above your baseline), it is likely that you are lactose intolerant. The baseline is the amount of hydrogen that is present in your breath before drinking the lactose solution.
Lactose tolerance test
In a lactose tolerance test, you will be given a drink of lactose solution, and then a sample of blood 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 are 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 will be given a glass of milk (about 500ml) and afterwards, your blood sugar levels will be tested. If your blood sugar levels do not rise, you may be lactose intolerant.
Stool sample
A stool sample may be taken from babies and young children to test for lactose intolerance. This is because large doses of lactose, such as those given in the lactose and hydrogen breath tests, are dangerous for young children.
The amount of acid in the stool sample is measured. If the baby or child is lactose intolerant, there will be a high amount of fatty acid, such as acetate, present. This is created by the bacteria in the colon breaking down the undigested lactose.
The stool sample can also be tested to determine whether there are any parasites present, which can also cause stomach problems.
Small bowel biopsy
As a small bowel biopsy is an invasive surgical procedure, it is rarely used to diagnose lactose intolerance. However, it may be carried out to confirm whether or not your symptoms are being caused by another condition, such as coeliac disease (a bowel condition that is caused by intolerance to a protein called gluten).
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). The procedure will be carried out under local anaesthetic (a painkilling medication), so it will not 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, lactose intolerance is likely. The biopsy will also reveal whether there is another underlying cause for your lactose intolerance.
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Treatment
Treatment for lactose intolerance depends on how sensitive you are to foods that contain lactose. The condition can usually be controlled by monitoring your diet.
If you decide to experiment with what you can and cannot eat, make sure that you introduce new foods gradually rather than all at once. This will help you to get used to any foods that you might be sensitive to.
Missing out on the nutrients provided by products that contain lactose can lead to deficiencies in calcium, plus other important minerals. It is particularly important for young children to have certain nutrients in their diet to ensure healthy growth and development.
If you or your child are extremely sensitive to lactose, talk to your GP about your diet. You may need to have regular bone mineral density checks, or you may be referred to a dietitian (an expert in diet and nutrition). They can advise you about what foods should be included in your (or your child’s) diet.
Milk
A major source of lactose is milk - cow milk, goat milk and sheep milk.
Depending on how mild or severe your lactose intolerance is, you may need to change the amount of milk in your diet. For example:
- 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 that you can try, such as soya milk. You can now also buy milk that is made from rice, oats, potatoes and even peas.
Dairy products
Other dairy products, such as butter, ice cream and cheese, can also contain high levels of lactose, Some dairy products may be easier to digest than others. Cheese, for example, usually contains less lactose than milk. In particular, fermented dairy products, such as yoghurts, are often easier to digest.
Fermented dairy products are products that have been broken down by substances, such as yeast, bacteria, or other micro-organisms. This means that the lactose they contain will already be partially broken down, and they may be easier to digest than fresh dairy products.
Possible dairy products you could try include:
- yoghurts, including probiotic yoghurts (that contain live bacteria)
- probiotic milk
- sour cream
- cottage cheese
- hard cheeses, such as Edam and Cheddar
It is important that you do not eliminate dairy products completely from your diet because they provide essential nutrients.
Food and drink containing lactose
Aside from dairy products there are also a number of food and drinks that contain lactose. Depending on how intolerant you are to lactose, you may need to remove them from your diet.
These include:
- salad cream, salad dressing and mayonnaise
- biscuits
- chocolate
- boiled sweets
- cakes
- peanut butter
- 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
Make sure that you check the ingredients of all food and drink products carefully because milk or lactose are often hidden ingredients.
The lactose contained within milk or milk ingredients will not be listed separately on the food label, so you need to check the ingredients list for milk or milk ingredients such as cheese, butter, cream or yoghurt as well.
Food labelling
Some foods may be labelled "reduced lactose". However, there are currently no rules to say how much less lactose a product must contain in order to be able to display this label. You should check the list of ingredients to find out exactly how much lactose the product contains.
If a product is labelled "lactose-free", it usually means that the product does not contain natural lactose. It is also a good idea to choose products with added calcium.
Lactose-free food and drinks
Food and drinks that do not contain any lactose include:
- all soya milks, yoghurts and some cheeses
- all milks made from rice, oats, quinoa, almonds, hazelnuts, coconut and potato
- all foods which carry the "dairy-free" or "suitable for vegans" signs
- carob bars
Lactose in medicines
Some prescription medicines, over-the-counter (OTC) medicines and complementary medicines may contain a small amount of lactose. While this is not usually enough to trigger the symptoms of lactose intolerance, it may be if your intolerance is severe, or if you are taking a number of different medicines.
If you need to start taking a new medication, you should check with your GP or pharmacist in case it contains lactose.
Lactase substitute
Lactose intolerance is usually caused by a deficiency of the enzyme called lactase (a protein that causes a chemical reaction to occur). A lactase substitute is available that can be taken to replace the lactase that your body cannot produce.
The lactase substitute comes in liquid form (usually as drops) that can be taken before a meal or added to milk. This can be very effective in helping your digestive system to digest the lactose in the meal. You can also take lactase pills (lactase enzyme capsules) before a meal.
Both lactase enzyme drops and capsules are available from most health foods shops.
Calcium
If you are unable to eat most dairy products, you may not be getting enough calcium in your daily diet. You can stock up on calcium by eating foods such as:
- broccoli
- cabbage
- okra
- kale (a leafy green vegetable)
- dried fruit
- soya drinks with added calcium
- soya beans
- tofu
- nuts (such as almonds, brazil nuts and sesame seeds)
- fish containing edible bones (for example, sardines, salmon, and pilchards)
Food supplements
You can also buy combined calcium and vitamin D supplements, available in tablet form, from most pharmacists.
It is important to check with your GP or dietitian whether you should be taking supplements as taking excessively high levels of calcium can cause kidney problems, constipation and tissue damage.
Lactose intolerance in children
If your child is lactose intolerant, they may be able to consume small amounts without experiencing symptoms. This is quite safe, but you may need to experiment to establish a comfortable threshold.
In some cases, your child may not be able to tolerate any quantity of dairy food at all. If so, your doctor can refer you to a dietitian for nutritional advice. There are also lactose-free formulas available for babies, while soya and nut milks make good substitutes for dairy milk, so older children can drink these instead.
Fish, tofu, nuts and green vegetables are also calcium rich and lactose free.
Your doctor or dietitian may recommend the use of lactase drops, as discussed above. These can be added to milk to help digest the lactose in it, making it safe to drink.
Remember that secondary lactose intolerance, brought on by a bout of illness such as flu or gastroenteritis, is only temporary. Avoid feeding your child dairy food during the illness, but a few days after symptoms have passed you can gradually reintroduce dairy into the diet.
Advice for breastfeeding women
It is perfectly safe to breastfeed your child if you're lactose intolerant. It does not put them at greater risk of becoming lactose intolerant and breastfeeding brings important health benefits to your baby.
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Complications
Dairy products such as milk are an important part of a healthy diet. They contain calcium, protein and vitamins such as vitamins A, B12 and D. For adults, the recommended daily allowance (RDA) for calcium is 700mg.
Lactose is also important because it helps your body to absorb a number of other minerals, including magnesium and zinc. These vitamins and minerals are important for the development of strong, healthy bones.
If you are lactose intolerant, getting the RDA of important vitamins and minerals can prove difficult.
This may put you at increased risk of developing the following conditions.
- Osteopenia, a condition where you have a very low bone mineral density. If osteopenia is not treated, it can develop into osteoporosis.
- Osteoporosis, a condition that causes your bones to become thin and weak. If you have osteoporosis, your risk of getting fractures and broken bones is increased.
- Malnutrition - this occurs when the food that you eat does not give you the nutrients that are essential for a healthy functioning body. If you are malnourished, wounds can take longer to heal and you may start to feel tired or depressed.
- Weight loss. Excessive weight loss can damage your health, and it can also lead to conditions such as osteoporosis.
If you are concerned that dietary restrictions are putting you at risk of complications, you should consult with a dietitian. They should be able advise you on your diet and whether you require food supplements.
Your GP should be able to refer you to a NHS dietitian free of charge. Alternatively, you can contact a private dietician.
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