Lactose intolerance

Lactose is a natural sugar that is found in milk. Lactose intolerance occurs when the body is unable to break down lactose and cannot absorb it into the blood. This can cause symptoms such as:

• a bloated stomach
• flatulence (wind)
• diarrhoea

Lactose

Lactose is found in the milk of mammals, including cows, goats, and sheep, and it is also added to many foods. Foods that contain lactose include:

• dairy products, such as cream, cheese, and yoghurt
• biscuits and chocolate
• some breakfast cereals

As well as being a good source of energy, lactose helps the body to absorb a number of minerals, such as calcium and magnesium.

Lactose intolerance

Lactose intolerance occurs when the body cannot break down and absorb lactose. It is usually caused by the lack of an enzyme, called lactase, which is produced by the small intestine. Enzymes are proteins that cause chemical reactions to occur.

If there is not enough lactase, the lactose cannot be absorbed and it passes into the colon (the large intestine), where it begins to cause symptoms.

How common is lactose intolerance?

It is estimated that around 5% of adults in the UK have lactose intolerance.

It is more common among people of some ethnic origins, and particularly people who do not traditionally have milk as part of their diet. Lactose intolerance is thought to occur in:

• between 50–80% of people of Hispanic, south Indian, black or Ashkenazi Jewish ethnicity
• almost 100% of people of American Indian, or Asian, ethnicity 

Outlook

Lactose intolerance can range from mild to severe, depending on how much lactose a person has in their diet and how well their body can digest it.

Lactose intolerance cannot be prevented. However, the condition’s symptoms can be reduced by avoiding certain foods that contain lactose. For example, it may still be possible to eat cheese and yoghurt, but not to drink milk.

For more severe lactose intolerance, it is possible to take a lactase substitute to help digestion. It may also be necessary to seek dietary advice to avoid becoming deficient in the other nutrients, such as calcium, that dairy products usually provide.

Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

Enzymes
Enzymes are proteins that speed up and control chemical reactions, such as digestion, in the body.