What is lactose intolerance and what are the symptoms?
Lactose is the main sugar in mammalian milk, for example cows, goats, and sheep. Lactose is broken down into glucose and galactose by the enzyme called lactase.
In lactose intolerance, lactase is either absent (alactasia) or deficient (hypolactasia).
This means lactose is not broken down and unabsorbed lactose passes into the colon where it is fermented. Lactose intolerance results in symptoms such as bloating, excess wind, abdominal pain and diarrhoea.
Types of lactose intolerance
Lactose intolerance can be divided into three categories:
- congenital alactasia is a rare condition inherited as an autosomal recessive trait. It results in life long complete absence of lactase
- primary lactase deficiency is an age-related condition, characterised by a progressive loss of lactase activity. This leads to a partial absence of lactase
- secondary lactose intolerance can follow any gastrointestinal illness where there has been damage to the brush border cells of the small intestine.
What is the link between lactose intolerance and coeliac disease?
Coeliac disease is a frequent cause of secondary lactose intolerance. A 2005 study involving people with lactose intolerance found that 24% of subjects had villous atrophy, confirming coeliac disease (1).
Untreated coeliac disease results in damage to the lining of the gut. The enzyme lactase is found in the brush border of the small intestine. This is why people with coeliac disease can be deficient in lactase at diagnosis.
Once established on a gluten-freeWhen a food has less than 20 parts per million (ppm) of gluten so it is safe for people with coeliac disease to eat. diet, the gut is able to heal and lactose digestion returns to normal. Lactose intolerance is therefore usually temporary. However, it can take up to a couple of years for lactase production to return to normal depending on how long it takes the gut to heal.
Diagnosis of lactose intolerance
The symptoms of lactose intolerance are very similar to those of coeliac disease. Lactose intolerance does not involve a response by the immune system and no antibodiesExist in the blood and are used by the immune system to attack viruses or bacteria. are produced.
Lactose intolerance should be considered in patients with on-going symptoms known to be following a glutenA protein that is found in the cereals wheat, barley and rye. -free diet. Lactose intolerance can be diagnosed by the Hydrogen Breath Test. This is a non-invasive test and has good sensitivity and specificity (2).
Many people with coeliac disease do not have lactose intolerance because enough lactase is available in parts of the small intestine that are unaffected. Foods which contain lactose can be an important source of calcium in the diet. It is important lactose intolerance is diagnosed before changing the diet.
Lactose intolerance is treated by avoiding or restricting lactose. The amount of lactose people can manage in the diet depends on the degree of lactase deficiency. Most people can tolerate the amount of lactose in one glass of milk.
People with lactose intolerance should be given dietary advice to make sure there is enough calcium in their diet from non-dairy sources. Some people may need to take calcium supplements. Individuals should have their diet assessed and advice should be given on an individual basis.
Lactose reduced milks are now available. Fermented dairy products, such as yoghurt, buttermilk, and cheese may be tolerated by most patients, because of the reduced level of lactose.
We have produced an information leaflet on lactose intolerance and coeliac disease that you can assess in the Members section.
All pre-packaged food bought in the UK is covered by EU wide food allergen labelling legislation. Milk is one of the 14 allergens that are covered by this legislation. This means that if milk is used as a deliberate ingredient, it must appear on the ingredients list, regardless of the amount used. An allergy advice box is only a recommendation and is not compulsory.
1 Ojetti V, Nucera G, Migneco A, et al (2005) High prevalence of Celiac Disease in Patients with Lactose Intolerance. Digestion. 71: 106-110.
2 Romagnuola J (2002) Using breath tests wisely in a gastroenterology practice: An evidence-based review of indications and pitfalls in interpretation. American Journal of Gastroenterology. 98:1113-1126.