Is lactose intolerance genetic?

Genetics usually plays a role in lactose intolerance, a condition in which the body is unable to digest lactose, the sugar found in milk.

There are four types of lactose intolerance, and genetics plays the lead role in two of them. The types of lactose intolerance include:

• Primary lactose intolerance
• Secondary lactose intolerance
• Congenital lactose intolerance (or alactasia)
• Developmental lactose intolerance

Both primary and congenital lactose intolerance have genetic causes. 

• Primary lactose intolerance is the most common type. This occurs when the amount of lactase the body makes dramatically declines with age. A person with primary lactose intolerance may have no problems as an infant ingesting lactose through either breastmilk or formula because their body produces enough lactase to digest it. But as they get older, the lactase they produce drops, making milk products difficult to digest. This issue occurs in two-thirds of all people, although some are more likely to show symptoms than others.

• Congenital lactose intolerance is a rare, inherited type of lactose intolerance. Only 1 in 60,000 babies is born lactose intolerant. It’s an inherited disorder in which someone doesn't produce lactase, making it impossible to digest lactose. Both the mother and father must pass on the same gene variant for the child to inherit this condition.

Risk factors for lactose intolerance include:

• Ethnicity
• Increasing age
• Premature birth
• Conditions affecting the small intestine
• Certain cancer treatments

Ethnicity plays an important part in the genetics of lactose intolerance. Lactose intolerance is most common in people of African, Asian, Hispanic and Native American descent. Historically, these groups consume lower amounts of milk, related to the availability of pastures and farm animals.

It's possible to be lactose intolerant due to factors other than genetics. Secondary lactose intolerance occurs when the amount of lactase in the body is decreased due to illness, injury or surgery.

Developmental lactose intolerance may occur in premature infants because they don’t have enough of the enzyme lactase needed to digest milk. However, this condition usually goes away on its own as the digestive system matures and can make more lactase.

Lactose intolerance can also look like or occur alongside other conditions, such as irritable bowel syndrome (IBS), anxiety and visceral hypersensitivity. It can be difficult for doctors to diagnose the condition in some cases. As with any other condition, you should always consult your healthcare provider if you’re experiencing symptoms. There are over-the-counter lactose intolerance supplements that may be helpful.

Published June 2022.