An intolerance to lactose

Lactose is a sugar found in milk and those people suffering from lactose intolerance are not able to digest and break this sugar down. The cells that line the small intestine produce an enzyme called lactase and people who are lactose intolerant have a shortage of this enzyme. If there is not enough lactase, the lactose cannot be absorbed and it passes into the colon (the large intestine), where it can start to cause symptoms. A lactose intolerance can sometimes be referred to as Lactase Deficiency.

Lactose intolerance

There is sometimes confusion between lactose intolerance and a cow milk allergy. A milk allergy is a reaction by the body’s immune system to one or more milk proteins and can be life threatening when just a small amount of milk or milk product is consumed. It is therefore important that the two are not confused. A milk allergy will generally appear in the first year of life, while lactose intolerance occurs more often in adulthood.

Lactose is most commonly found in the milk of mammals (cows, goats and sheep) although it can also be found in other food products including:

  • Dairy products (i.e. butter, cream, cheese, yoghurt)
  • Biscuits, cakes and chocolate
  • Processed breakfast cereals
  • Salad dressings
  • Ice cream
  • Packets of instant potatoes and instant soup

Some cultures, that aren’t used to having milk as part of their diet, are more susceptible to developing a lactose intolerance than others. These include people of Hispanic, south Indian, black, Ashkenazi Jewish, American Indian, or Asian, ethnicity. Also babies born prematurely are more likely to have a lactase deficiency since lactase levels only increase in the third trimester of pregnancy.

There are two types of lactase deficiency:

Primary Lactase Deficiency

This runs in families and is genetically inherited. It will generally develop between the ages of 2 and 20 when your lactase production decreases, often when breastfeeding or bottle-feeding has stopped. However the symptoms may not develop or be noticeable for several years.

Secondary Lactase Deficiency

This is caused by an injury to the small intestine and can occur at any age although is more common in infancy. It can also develop as a result of surgery to your small intestine, some medications or other medical conditions including coeliac disease, gastroenteritis, Crohn’s disease and chemotherapy.

Most people with lactose intolerance can tolerate some amount of it in their diet and therefore the symptoms will vary from mild to severe depending on the amount of lactose an individual can tolerate. A person with lactose intolerance will start to feel uncomfortable anywhere from 30 mins to 2 hours after digesting lactose. These symptoms include:

  • abdominal pain
  • abdominal bloating
  • wind
  • diarrhoea
  • nausea

Lactose intolerance is usually diagnosed after speaking with your doctor, who is likely to give you one of the following tests:

Lactose Tolerance Test – after taking a lactose solution drink, a sample of blood is taken from the arm. This is then tested to see how much glucose it contains. If the blood sugar levels rise slowly, or not at all, you will be lactose intolerant. This is due to the fact that your body is unable to break down the lactose in glucose.

Hydrogen Breath Test – following consumption of a lactose-loaded drink your breath is analysed at regular intervals to measure the amount of hydrogen in it. Usually there is very little hydrogen detectable in the breath so if it then contains high levels of hydrogen this is due to the undigested lactose.

Stool Acidity Test – since the above tests involve a large intake of lactose these are generally not given to infants or very young children since it can be dangerous for them. In these instances a stool acidity test can be used. This will measure the amount of acid in the stool. If there is a high amount of fatty acid, such as acetate present, a lactose intolerance will be diagnosed.

If you suffer with a lactose intolerance it can usually be controlled by monitoring your diet. You may find that you can eat many dairy products in some quantity or another. It is, however, important to ensure that you are getting enough calcium in your diet if you have to avoid milk and other calcium rich dairy products. This can be done by increasing your intake of foods such as fish with soft bones (i.e. salmon, sardines, pilchards), dark green vegetables (i.e. spinach, broccoli, kale) and dried fruits.

Over-the-counter lactase enzyme drops or tablets are now available; these are taken when consuming milk or milk products and can make them more tolerable for people with a lactose intolerance. In addition, you can now purchase lactose-free and lactose-reduced milk and milk products.

Information contained in this Articles page has been written by talkhealth based on available medical evidence. Our evidence-based articles are certified by the Information Standard and our sources are available on request. The content is not, though, written by medical professionals and should never be considered a substitute for medical advice. You should always seek medical advice before changing your treatment routine. talkhealth does not endorse any specific products, brands, or treatments.

Information written by the talkhealth team

Last revised: 6 December 2012

Next review: 14 August 2014