Lactose Intolerance

What else is it called?

  • Alactasia
  • Dairy product intolerance
  • Hypolactasia
  • Lactose malabsorption
  • Milk sugar intolerance

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What causes it?

Lactose Intolerance is characterised by your body’s inability to break down lactose for energy. Lactose is a sugar which is found primarily in dairy products such as milk, yoghurt and cheese. It is recommended that if you have this disorder you avoid lactose containing products, so you do not suffer from the side effects.

Due to this deficiency your body is unable to breakdown lactose or can only break down a small quantity of it.

Currently, there are four known types of lactose intolerance, these are:

  • Primary lactose intolerance
  • Secondary lactose intolerance
  • Congenital lactose intolerance
  • Development lactose intolerance

Primary lactose intolerance is caused through a genetic disorder from your parents. This may be due to an error within the MCR gene which is inherited from your parents. This gene usually allows your body to break down lactose in your small intestine for energy by producing the substance lactase. Symptoms occur when you become less reliant on milk, such as after the weaning stage. This is when your body loses the ability to break down lactose. Symptoms with this disorder may not present until adulthood.

Secondary lactose intolerance is caused by a shortage of the substance lactase within your small intestine. This intolerance is caused through another primary cause. Some other causes of secondary lactose intolerance may be coeliac disease, chemotherapy, crone’s disease and long courses of antibiotics.

Congenital lactose intolerance is caused by a genetic disorder in the gene which makes lactase. This is a rare form of lactose intolerance and becomes apparent within infancy and new born babies.

Developmental lactose intolerance is caused when the new born baby is born prematurely. This occurs due to the small intestine not being fully formed in the new born body. This type of lactose intolerance usually gets better as the baby gets older.

Tolerance to lactose is specific to the individual and you may be able to consume more lactose containing foods then someone else who has been diagnosed with lactose intolerance.

How common is it?

Approximately 65% of the current world’s population has the inability to break down lactose after infancy. Higher prevalence of this condition exists in east Asian where this disorder can affect up to 90% of the population. Also, within some regions of Finland, it is estimated to affect 1- 60,000 new born babies.

Secondary lactose deficiency is the most common cause of lactose intolerance within the United Kingdom.

What are the signs and symptoms?

If you consume food or drink containing lactose when you have lactose intolerance, symptoms will usually present between 30 minutes to 2 hours. Symptoms may include:

  • Diarrhoea
  • Stomach cramps and abdominal pain
  • Bloating
  • Excessive gassiness
  • Nausea
  • Dehydration

Weight loss

How is it diagnosed?

It may be suggested by your general practitioner [GP] to keep a food diary before coming to your appointment. This would be used to write down any symptoms you experience after you have after eating certain foods. It may also be suggested to remove lactose containing foods from your diet to see if you notice a difference in the symptoms, these would then be reintroduced to identify which foods cause the symptoms.

Lactose intolerance can be diagnosed by a hydrogen breathe test. This would involve you fasting overnight and then once you arrive at your appointment you will be asked to breathe into a large balloon. After this you will be given an oral solution of lactose and asked to repeat the balloon test. If there is more hydrogen in the balloon, then the usual baseline amount then this is an indication for lactose intolerance. This is because lactose intolerance can cause the bacteria in your large intestine to produce more hydrogen than usual.

Another test which your health professional may perform would be a bowel biopsy. This is done to check your lactase levels and make sure that there is not a primary cause of this such as coeliac disease due to damage to the lining of your gut. A bowel biopsy involves placing a fine needle into your bowl to check the levels of lactase in there. You will be given pain relief to make sure that you do not feel any pain. If you have low levels of this substance, then this test would confirm lactose intolerance. This is generally not a painful procedure as this is done with pain relief but may be a little uncomfortable.

For infants who cannot undergo a bowl biopsy then it may be suggested that your GP performs a stool acidity test. This is done to check for high levels of lactose in stool samples which would ordinarily be absorbed by your body.

Other tests may include a lactose intolerance test or milk test. This would involve checking your blood sugar levels by a blood test and then drinking a lactose oral solution. The health care professional will then perform another blood test. If you have little or no increase in blood sugar levels, then this can be an indication of lactose intolerance.

testing lactase levels this part is looking at lactose intolerance, but the bowel biopsy is also taken to check for damage in the lining of the gut, which is typical in coeliac disease.

Can it be treated?

Currently there is no treatment for lactose intolerance. Most people with lactose intolerance can eat small amounts of lactose containing foods. The best thing you can do for this condition is to avoid foods and beverages that contain lactose or only consume these in small amounts.. Dairy products which are naturally low in lactose, yoghurts can be tolerated by many with lactose intolerance, as well as cured cheese, plant based beverages such as almond milk and soybean beverages and products labelled lactose free.

There some enzyme containing lactase over the counter medications you may want to consider. These aim to put the substance lactase into your body, so you can absorb lactose. These may help you to not suffer with the symptoms of lactose intolerance.

Probiotics are sometimes used to treat gastrointestinal disorders. Probiotics are live bacteria that come in an oral solution, these bacteria may help to break down some of the lactose you consume so your body does not present symptoms.

Do my family need to be tested?

Lactose intolerance can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.

If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.

If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.

Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inherited lactose intolerance. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.

If you have previously had a child with lactose intolerance and go on to have further children, their Newborn Screening test should be carried out within 24-48 hours of birth.

Relevant Organisations


References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing [Resource Library No: LCM039].

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