Health & Wellbeing

Lactase deficiency types, causes and dietary changes

By Anna Sawkins

Feb 23, 2022

Lactase deficiency types, causes and dietary changes

Lactose is a type of sugar found in milk, and products made from milk, such as yoghurts and cheeses. Lactose intolerance is a common digestive problem where the body is unable to digest lactose properly. The most common symptoms of lactose intolerance include:

  • flatulence
  • stomach ache
  • nausea
  • bloating
  • diarrhoea

Symptoms usually occur within an hour or two of ingesting milk (or other lactose-containing foods) and their severity depends on the amount of lactose that has been consumed. Lactose intolerance can range from mild to severe, and the amount of lactose required to trigger symptoms varies from person to person.

Causes of Lactose Intolerance

Lactose intolerance is caused by a deficiency of a digestive enzyme called Lactase. Enzymes are proteins which help chemical reactions to occur, and digestive enzymes enable reactions that break food molecules down into smaller, more digestible components, which can then be absorbed and utilised by the body. Different digestive enzymes help to break down different types of food.

Lactase helps your body to break down lactose into glucose and galactose in the small intestine. If there is not enough lactase present in the small intestine, then lactose passes along the digestive system to the large intestine, where it ferments and breaks down into acids and gases - which cause the unpleasant symptoms associated with lactose intolerance.

Lactase is produced by specialised cells in the walls of the small intestine. When these cells do not provide enough lactase (lactase deficiency), this is what is known as lactose intolerance.

There are different types of lactase deficiency

  • Primary lactase deficiency is a genetically inherited condition and the most common cause of lactose intolerance worldwide. In countries and cultures with a traditionally low level of dairy consumption (such as much of the Asian continent) the majority of people don’t need lactase because they don’t consume milk (other than in infancy, when they need to digest breast milk) and so there is a genetic predisposition for lactase production to decrease after infancy, when breast or bottle feeding is stopped. It is estimated that up to 70% of the world’s population has a primary lactase deficiency.
  • Secondary lactase deficiency is caused by a problem with the small intestine. In the UK, secondary lactase deficiency is the most common cause of lactose intolerance. It can be caused by a medical condition (such as gastroenteritis, Crohn’s disease or coeliac disease), surgery/injury to the small intestine or by specific medications/treatments (including chemotherapy). It can also develop later in life as the body’s ability to produce lactase decreases with age.
  • Congenital lactase deficiency is a rare genetic condition, found in newborn babies, where they produce very little or no lactase meaning they cannot digest milk of any kind, including breast milk.
  • Developmental lactase deficiency is a (usually) temporary lactose intolerance found in some premature babies, due to their small intestine not being fully developed before they were born. In most cases, the condition improves with age.


The most effective treatment for lactose intolerance is to reduce the amount of lactose in your diet. There are many lactose-free and dairy - free alternatives available to substitute for dairy products. However, it is essential to ensure that you still get all the minerals and vitamins that you need, so it is recommended that you consult with your nutritionist before making any significant changes to your diet.

There are also a growing number of scientific studies which suggest that probiotics may help reduce the symptoms of lactose intolerance for some individuals. In particular, there is evidence that Lactobacillus Acidophilus (Bargaoui, 2004), which is found in some probiotics, may help to improve the symptoms of lactose intolerance.

It is important to note that the symptoms of lactose intolerance are also associated with a range of other conditions. Should you suspect that you have lactose intolerance, always seek medical advice.

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