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Lactose intolerance


milk in glass

Lactose is a sugar found naturally in milk. It is important to distinguish between lactose intolerance and milk allergy, because milk allergy can cause severe reactions. (See the section on milk allergy.)

Lactose intolerance is caused by a shortage of the enzyme lactase, which is needed to break down lactose so it can be absorbed into the bloodstream. When someone doesn't have enough of this enzyme, lactose isn't absorbed properly from the gut, which can cause symptoms such as bloating and diarrhoea. This condition normally appears in adults because people's levels of lactase begin to decrease after childhood. Some children are born with lactose intolerance, but this is rare.

Lactose intolerance is more common in certain countries and ethnic groups than in others. In communities where milk is not traditionally part of the typical adult diet, a much bigger proportion of people are affected. For example, in South America, Africa and Asia, more than 50% of the population are intolerant to lactose, rising to nearly 100% in some parts of Asia. In the UK, Ireland, Northern Europe and America, we think, on average, that about 5% of the adult population have this condition.

Digestive diseases or injuries to the small intestine can sometimes cause lactose intolerance, because damage to the lining of the small intestine may reduce the amount of lactase produced. In extremely rare cases, the condition can be inherited.

Milk from animals including cows, goats, sheep and humans all contain lactose. This means that goats' milk and sheep's milk aren't suitable alternatives to cows' milk for people who are intolerant to lactose. There is no medical treatment for lactose intolerance, but symptoms can be avoided by controlling the amount of lactose in the diet. Adults with lactose intolerance can often have a small amount of milk without reacting.

Since 25 November 2005, food labelling rules require pre-packed food sold in the UK, and the rest of the European Union, to show clearly on the label if it contains milk (or if one of its ingredients contains it). Bear in mind that there could still be foods on the shelves that were produced before this date.



People with lactose intolerance often find that they can eat cheese and yoghurt without any problems. Cheese contains much less lactose than milk. Yoghurt contains a similar amount of lactose to milk, but it still seems to be easier to digest for people with lactose intolerance. This might be something to do with the bacteria used to make it.