Is Lactose Intolerance Genetic?

If you’ve ever noticed bloating, stomach cramps, or diarrhea after drinking milk, you may have wondered if lactose intolerance is genetic. The short answer: yes, genetics play a major role in whether you can comfortably digest dairy as an adult.

Lactose intolerance affects more than two-thirds of adults worldwide, but it doesn’t affect everyone the same way. Some people lose the ability to digest dairy early in life, while others maintain it into adulthood. Understanding the genetic side of lactose intolerance can explain why.

What Causes Lactose Intolerance?

Lactose intolerance happens when the body produces too little of an enzyme called lactase, which is needed to break down lactose, the natural sugar in milk. Without enough lactase, undigested lactose moves into the large intestine, where gut bacteria ferment it—leading to gas, bloating, abdominal pain, and diarrhea.

There are two main genetic forms:

• Congenital lactase deficiency (very rare): Babies are born with little to no ability to produce lactase, usually due to mutations in the LCT gene. Without treatment, this can cause severe diarrhea and weight loss in infants.
• Adult-type hypolactasia (common): In most people, lactase production decreases after childhood. This is controlled by a nearby gene called MCM6, which can “switch off” the LCT gene over time.

Why Some People Can Still Digest Dairy

Not everyone develops lactose intolerance. In fact, about one-third of adults worldwide maintain the ability to digest lactose throughout life. This is called lactase persistence.

Researchers have found that:

• Variants in the MCM6 gene regulate whether lactase production continues or declines after childhood.
• People with at least one copy of the “persistence” variant usually digest dairy well into adulthood.
• This trait likely evolved thousands of years ago in populations that relied on dairy farming.

For example, only about 5% of Northern Europeans are lactose intolerant, compared with up to 90% of East Asians and 70–100% of some African and Middle Eastern groups.

Is Lactose Intolerance Inherited?

Yes—genetics are the strongest factor. If your parents or grandparents are lactose intolerant, you’re more likely to be as well.

• Autosomal recessive inheritance: Congenital lactase deficiency requires both copies of the LCT gene to be altered.
• Dominant inheritance: Lactase persistence variants are dominant, meaning only one parent needs to pass it on for you to keep digesting dairy.

Can You Be Tested for Genetic Lactose Intolerance?

Several options exist:

• Genetic testing: Identifies variants in the LCT or MCM6 genes.
• Breath hydrogen test: Measures gases produced after drinking lactose-containing liquid.
• Elimination diet: Removing dairy and reintroducing it slowly can reveal intolerance.

Living With Lactose Intolerance

Even if lactose intolerance runs in your family, you can still manage symptoms and enjoy many foods:

• Try lactose-free milk or plant-based alternatives (almond, soy, oat).
• Choose aged cheeses (like Parmesan or cheddar), which are naturally low in lactose.
• Experiment with yogurt, since live cultures help break down lactose.
• Ask your doctor about lactase enzyme supplements before meals.

FAQs

1. ‍Can lactose intolerance skip a generation? Yes. Some family members may inherit lactase persistence variants, allowing them to digest dairy while others cannot.‍
2. If I’m lactose intolerant, can I ever eat dairy again? Most people can tolerate small amounts or certain dairy products like cheese and yogurt. Severity varies person to person.‍
3. Is lactose intolerance more common in certain ethnic groups? Yes. Rates are highest in East Asian, West African, Arab, Jewish, and Mediterranean populations, and lowest in Northern Europeans.

Key Takeaway

Lactose intolerance is largely genetic. While lifestyle and gut health can play a role, your DNA determines whether you continue making the lactase enzyme into adulthood. If you notice recurring symptoms after eating dairy, talk with a healthcare provider about testing and management options.

Request an appointment with a BASS Medical Group provider to learn more about digestive health and personalized care.