Lactose intolerance

It may be stomach ache, gas or a bloated feeling: some people get digestive problems when they have drunk milk or eaten dairy products. Someone who reacts sensitively to dairy products can only tolerate milk sugar in small quantities, if at all. The medical name for this sensitivity is lactose intolerance.

At a glance

  • After drinking milk or eating dairy products, some people have digestive problems.
  • This may be due to a lactose intolerance. Those affected can only tolerate small amounts of lactose (the sugar component of milk).
  • Around 5 to 15 percent of all Europeans have lactose intolerance, with it being least common in the countries of Northern Europe.
  • People with a lactose intolerance can live free from symptoms by modifying their diet. There is no cure, however.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

Lactose intolerance: table with glasses of milk and a bowl of rice pudding.

How common is lactose intolerance?

Globally, lactose intolerance is very common. But there are big differences between regions and populations.

Approximately 5 to 15 percent of people in Europe have lactose intolerance.

In Europe around 5 to 15 percent of people cannot tolerate milk sugar. Lactose intolerance is least common in Northern Europe. In contrast, in Africa or East Asia, 65 to over 90 percent of adults have problems when they consume milk or dairy products.

Lactose intolerance is very rare in children below the age of 5. It usually only develops during adolescence and adulthood.

What is lactose intolerance?

Anyone who gets stomach ache, gas, or diarrhea after drinking milk or eating dairy products may possibly only tolerate milk sugar (lactose) in small amounts. The medical term for this sensitivity is lactose intolerance or milk sugar intolerance.

Someone may react sensitively to milk for reasons other than lactose intolerance. For this reason, it is important for a doctor to first diagnose lactose intolerance before that person changes their diet. This particularly applies to children, adolescents, and other people who have an increased need for calcium.

Important: Lactose intolerance is not an allergy. The difference is very important. While people with lactose intolerance can sometimes consume relatively large amounts of milk or dairy products without experiencing severe symptoms, people with a milk allergy have a strong reaction to even the smallest amounts of milk or dairy products.

What are the symptoms of lactose intolerance?

Someone who cannot tolerate much lactose usually suffers symptoms shortly after drinking milk or eating dairy products. The quantity of lactose that triggers symptoms varies widely between one person and the next.

Typical symptoms of lactose intolerance include: a bloated stomach and excessive gas, feeling full, lower abdominal pain, diarrhea, nausea and vomiting and constipation.

Someone with a lactose intolerance typically complains of, for example:

  • a bloated stomach
  • a full feeling
  • lower stomach pain
  • excessive gas
  • diarrhea
  • nausea and vomiting
  • sometimes constipation, too

Symptoms occur at the earliest half an hour after consuming food or drinks containing lactose. They are at their most severe approximately one and a half to two hours after consumption but they may persist for longer.

What are the causes of lactose intolerance?

Lactose intolerance is usually hereditary. Doctors call this primary (i.e. inherited) lactose intolerance.

A baby’s body is adapted to be fed by breast milk alone. It produces the enzyme lactase to break down the breast milk during digestion. This protein breaks down the sugar in the milk (lactose) inside the baby’s small intestine so that it can be absorbed into the bloodstream.

After the lactation (breastfeeding) period, the digestive system gradually switches to other foodstuffs. The body then produces much less lactase, and can only break down smaller amounts of lactose. Some people do not produce enough lactase to break down the lactose in the food and drink that they consume.

If an adult consumes more lactose than the lactase in their body can break down, some lactose remains in the small intestine. This unabsorbed lactose then moves into the large intestine (colon), where it is broken down by intestinal bacteria. This process is known as fermentation. More gases and other by-products are then produced in the gut. They cause the complaints.

How well an adult can tolerate foods containing lactose differs from one individual to the next and depends on a person’s genetic predisposition.

For more detailed information, for example on the causes of lactose intolerance, go to

How is a lactose intolerance diagnosed?

If anyone suspects that they may not tolerate lactose well, it’s best for them to consult their family doctor. In most cases, they will then be referred to a specialist in gastroenterology (diseases of the digestive system) for tests.

The following tests are used to diagnose lactose intolerance:

  • Diet or exclusion test: this test involves the patient excluding all milk and dairy products from their diet for a certain time. Afterwards, they allow themselves a certain amount of lactose on board, and the doctor monitors how the body responds.
  • Lactose intolerance test: the blood glucose level is measured before and several times after drinking a lactose solution. This enables the doctor to see whether the body can break down and absorb the lactose.
  • Breath test: after the patient drinks a lactose solution, the hydrogen content in their exhaled breath is measured. This value is usually elevated if a lactose intolerance is present.

It is not necessary for each of these tests to be conducted. In Germany, the breath test is the standard procedure.

Important: A diagnosis cannot be made on the basis of these measurements alone. Lactose intolerance can only be identified as the cause if typical symptoms occur during testing.

How is lactose intolerance treated?

Primary (inherited) lactose intolerance cannot be treated. However, people can live their lives free from symptoms by removing milk and dairy products from their diet.

Research to date indicates that the best way to reduce symptoms is to consume lactose in limited amounts and to only drink milk together with other foods.

Secondary lactose intolerance refers to a lactose intolerance that is caused by another disease rather than being inherited. In such cases, it is important to discover and treat the exact cause. If the intestinal mucosa recovers with treatment, the symptoms also vanish.

Important: Some people take preventive supplements containing artificially produced lactase – the protein that breaks down lactose in the small intestine – to improve their tolerance of lactose. These dietary supplements are intended to support the lactose breakdown process. However, studies have yet to provide any convincing evidence that they help relieve the typical symptoms of lactose intolerance. It is also unclear whether prebiotics or probiotics intended to promote healthy intestinal flora are of any benefit to those with lactose intolerance. Probiotics contain live bacteria, while prebiotics contain indigestible dietary fibers.

What is important in everyday life with lactose intolerance?

A balanced diet is also possible without dairy products. But if the person cuts milk from their diet, they should be sure to get enough calcium. This can be found, for example, in green vegetables such as spinach and kale, and in mineral water that contains calcium. Other good calcium providers are mature cheeses such as Parmesan and old Gouda, which many people with lactose intolerance are able to eat without problems.

Someone who finds it difficult to exclude dairy products can experiment to see how much lactose they can tolerate without triggering symptoms. They can then allow themselves to consume this amount, combined with other foods, over the course of the day.

In most cases, it’s not necessary to cut out all foods containing lactose. The following quantities are normally well tolerated – especially if they are consumed together with other foods as part of a meal:

  • up to 12 grams of lactose in one serving – for example, 250 milliliters of milk
  • up to 24 grams of lactose over the course of one day – for example, 500 milliliters of milk

Those who suffer badly from lactose intolerance usually avoid dairy products altogether. However, this can be difficult when not eating at home. Many ready meals and convenience foods also contain some lactose.

For more information about living with lactose intolerance and shopping tips, visit

Where can I find more information about lactose intolerance?

There is more information on lactose intolerance at (in German).

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen – IQWiG).

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