Is Lactose Intolerance Genetic? Find Out What It Means


Lactose intolerance is a widespread condition that affects many individuals globally. It’s a health condition where people struggle to digest lactose, a sugar found in milk and other dairy products.

Lactose intolerance leads to symptoms like stomach aches, bloating, gas, and diarrhea when one consumes foods with lactose.

It’s not just a health issue, but it also has cultural and evolutionary significance affecting human nutrition, diversity, and adaptation.

The prevalence of lactose intolerance varies widely among different populations, from less than 10% in parts of Europe to over 90% in areas of Africa and Asia. This variation is due to a complex mix of genetic factors and the environment affecting lactose digestion.

In this article, we’re going to dive deep into the biology, history, and genetics of lactose digestion.

Quick Note On Is Lactose Intolerance Genetic?

Yes, lactose intolerance is often genetic. The condition, known as primary lactose intolerance, is largely due to the body’s reduced ability to produce lactase, an enzyme needed to digest lactose, as people age. This genetic predisposition is most common in adults with a family history of the condition. Additionally, rare forms, such as congenital lactase deficiency, occur when infants are born with little or no lactase enzyme, leading to severe symptoms from milk consumption.

The genetic aspect of lactose intolerance is primarily associated with variations in the LCT gene, responsible for lactase enzyme production. This leads to lactase non-persistence in most adults, where the production of lactase drops significantly after infancy, resulting in lactose intolerance. Conversely, in certain populations, a genetic trait known as lactase persistence allows some adults to continue digesting lactose effectively.

Beyond genetics, lactose intolerance can also stem from non-genetic factors, including injuries to the intestine, specific digestive diseases, or alterations in the gut microbiota, highlighting the complexity of its origins.

Keep on reading the article for in-depth insights on how it evolved and what are the ways to manage it.

How Does Lactose Digestion Work?

Lactose is a type of sugar composed of two simpler sugars: glucose and galactose. It’s the main carbohydrate found in the milk of mammals, serving as a critical energy source for infants.

To use lactose, mammals need an enzyme called lactase-phlorizin hydrolase (LPH) located on the cells of the small intestine.

This enzyme has two functions:

  1. one that breaks down lactose (lactase)
  2. one that breaks down phlorizin, a plant compound that inhibits sugar transporters.

The latter function likely evolved to protect mammals from plant toxins.

The Genetics of Lactose Intolerance

The gene called lactase (LCT) encodes the LPH enzyme and is located on chromosome 2q21.

In most mammals, including humans, LCT gene expression is high during infancy but declines after weaning, reducing LPH activity and leading to lactose intolerance.

This phenomenon is known as lactase non-persistence (LNP) or primary hypolactasia.

However, in some human populations, LCT expression remains high throughout adulthood, allowing lifelong lactose digestion. This condition is known as lactase persistence (LP) or adult-type hypolactasia.

Genetic differences between LNP and LP primarily depend on genetic variations that impact the transcriptional regulation of the LCT gene. These variations affect the transcription of the LCT gene in response to developmental and nutritional cues.

These variations occur in a region near LCT, within an intron of another gene called MCM6. Depending on which gene variations a person inherits, LCT expression may either continue or stop after weaning.

The most common genetic variation associated with lactose intolerance is -13910C, the ancestral variant. Individuals who inherit two copies of this variant (CC genotype) have low LCT expression and low LPH activity, resulting in lactose intolerance.

Those with one copy (CT genotype) have intermediate LCT expression and variable lactose tolerance, while those with the -13910T variant (TT genotype) have high LCT expression and are lactose-tolerant.

In addition to these variations, there may be other genetic factors, like variations in the number of gene copies, and epigenetic factors that influence lactose intolerance.

So, is lactose intolerance genetic? The answer is, largely, yes.

Understanding the genetics behind lactose intolerance helps us understand this widespread condition, its cultural and evolutionary implications, and future treatment strategies.

It’s a fascinating field that continues to provide insights into human evolution, health, and dietary adaptations.

Here is a video where I explain lactose intolerance and its history briefly.

The History of Lactose Tolerance and Intolerance

Lactase persistence (LP) and lactase non-persistence (LNP) have evolutionary origins that intrigue scientists.

LP is considered a new trait that arose multiple times independently in different human populations due to natural selection, while LNP or lactose intolerance is considered an ancestral trait common to most mammals and humans.

The earliest evidence of LP dates back about 10,000 years ago, coinciding with the emergence of animal domestication and dairy farming.

These cultural practices likely gave a survival advantage to individuals who could digest lactose, allowing them to access a rich source of calories, protein, and nutrients from milk.

Four main genetic variations are associated with LP, reflecting geographic origin and history.

However, not all cases of LP can be explained by these four variants. Other genetic factors may influence LCT expression and lactose digestion, such as gene copy number variations, modifications in gene expression, and interactions with other genes.

Environmental factors, like gut microbiota composition, dietary habits, and lactose intake, may also affect lactose tolerance.

Difference Types of Lactose Intolerance

Lactose intolerance can be categorized into two types: primary and secondary lactose intolerance.

Primary lactose intolerance is the most common type. It’s a genetically inherited condition where the body’s production of lactase decreases over time.

This genetic lactose intolerance tends to appear after the age of two when the body begins to produce less lactase.

On the other hand, secondary lactose intolerance isn’t genetic. Instead, it occurs when the small intestine reduces the production of lactase after an illness, surgery, or injury to the gut.

Conditions like celiac disease, inflammatory bowel disease, or intestinal infections can trigger secondary lactose intolerance.

The good news is, secondary lactose intolerance can often be reversed by treating the underlying condition causing it.

How Genetic Testing is Used to Find Out if You Are Lactose Intolerant

If you’re lactose intolerant, you might feel sick after having foods or drinks that contain lactose.

Diagnosing lactose intolerance can be tough, as the symptoms can be similar to other stomach issues. Doctors need to carefully look at your medical history, do a physical exam, and perform some lab tests to make sure lactose intolerance is the cause of your symptoms.

Genetic testing can be used to see if you have the genes that cause lactose intolerance.

This testing can help doctors understand why you might be having stomach issues, and can even provide information about your ancestry and evolutionary history.

There are different types of genetic tests that can be used for lactose intolerance, depending on what information you need:

  • Restriction fragment length polymorphism (RFLP) analysis
  • Allele-specific PCR (AS-PCR)
  • DNA microarray
  • Direct DNA sequencing

Some lab tests that can be used include hydrogen breath, lactose tolerance, and stool acidity tests.

These tests look at things like how much hydrogen is in your breath, your blood sugar levels after drinking a lactose solution, the pH of your stool after drinking a lactose solution, and if you have the lactose intolerance gene.

Relation Between Lactose Intolerance and Gut Microbiome

The gut microbiome, which is a community of beneficial bacteria residing in our intestines, plays a vital role in our overall health and our body’s ability to process different types of food.

In the context of lactose intolerance, the gut microbiome can be a critical player.

When the body can’t digest lactose due to low lactase production, the undigested lactose passes into the colon, where it’s fermented by the gut bacteria. This process produces gas, leading to common lactose intolerance symptoms like bloating and flatulence.

Interestingly, some gut bacteria are capable of breaking down lactose. Therefore, the composition of the gut microbiome might influence the severity of lactose intolerance symptoms.

For instance, some individuals might have more lactose-digesting bacteria, enabling them to handle lactose better than those who don’t.

Consequently, modifying the gut microbiome through probiotics or other dietary changes could potentially help manage the symptoms of lactose intolerance.

Other Factors That Can Cause Lactose Intolerance

Besides genetics and the gut microbiome, there are several other factors that can contribute to the development of lactose intolerance:

  1. Aging: As we age, the production of lactase in our bodies can decrease, leading to lactose intolerance. This is one of the most common reasons why many adults experience lactose intolerance.
  2. Non-exposure to Diary: If a person lactase producing cells are not exposed to Diary products, they may become less in number over time, and sudden exposure to Diary can lead to intolerance. However, over time the person can become tolerant again.
  3. Gastrointestinal disorders: Certain gastrointestinal conditions like celiac disease, Crohn’s disease, and irritable bowel syndrome can damage the lining of the small intestine, which is where lactase is produced. This can lead to lactose intolerance, often termed as secondary lactose intolerance.
  4. Certain medications: Some medications or antibiotics can interfere with lactase production or functionality in the small intestine, leading to temporary lactose intolerance.
  5. Surgery: Surgical procedures involving the digestive system, particularly those that affect the small intestine, can sometimes cause lactose intolerance.
  6. Infections: Intestinal infections can temporarily damage the lining of the intestines, impacting the production of lactase and leading to temporary lactose intolerance.
  7. Chemotherapy or radiation therapy: These treatments can damage the cells lining the small intestine, which can result in temporary lactose intolerance.

Can Lactose Intolerance and Tolerance Interchange Over Time?

It’s possible for lactose tolerance to change over time. Most people develop lactose intolerance as they grow older due to a decrease in the production of lactase, the enzyme responsible for breaking down lactose.

This condition, known as primary lactase deficiency or primary lactose intolerance, is genetic and usually appears in adulthood.

Conversely, in some cases, those diagnosed with lactose intolerance during their early life may find they can handle lactose better as they grow older. These are mostly secondary lactose intolerance cases.

This can be due to the changes in their gut microbiome composition or adaptation of their digestive system to regular lactose consumption.

However, this isn’t typically the norm, and for most people, once the lactose intolerance gene manifests, it tends to remain a lifelong condition.

Alternative Food Choices for Lactose Intolerant Individuals

Lactose intolerance can restrict dairy consumption, but with thoughtful planning, you can still enjoy a diverse and nutrient-rich diet.

There are numerous lactose-free or low-lactose options available that can substitute for traditional dairy products for conditions like lactose intolerance and galactosemia, allowing individuals with these conditions to avoid discomfort without compromising on nutrition:

  1. Lactose-free milk and dairy: These are regular dairy products treated with the enzyme lactase, which breaks down lactose, making them easier for people with lactose intolerance to digest. They provide the same nutrients as regular dairy.
  2. Non-dairy milk alternatives: Almond milk, soy milk, rice milk, oat milk, and coconut milk are all great alternatives for individuals with lactose intolerance. They can be used in cooking and baking just like regular milk. Some of these might be fortified with calcium and vitamin D to match the nutritional content of regular milk.
  3. Hard and aged cheeses: These types of cheeses, like cheddar, swiss, and parmesan, are lower in lactose and might be well-tolerated by some people with lactose intolerance.
  4. Yogurt: Some people with lactose intolerance can tolerate yogurt, especially those with live and active cultures. The bacteria used in the yogurt-making process naturally break down lactose.
  5. Butter and ghee: These are high in fat and contain minimal lactose, so some individuals with lactose intolerance can consume them without experiencing symptoms.
  6. Calcium-rich non-dairy foods: To ensure you’re getting enough calcium in your diet, incorporate foods like broccoli, kale, canned fish with bones (like salmon and sardines), tofu processed with calcium sulfate, and fortified non-dairy beverages and cereals.
  7. Probiotics and fermented foods: Foods like kimchi, sauerkraut, and other fermented foods, as well as probiotics, can help promote gut health and improve lactose digestion.

The ability to tolerate lactose varies greatly from person to person; what works for one person might not work for another.

It’s essential to monitor your body’s reactions to different foods and consult with a dietitian or healthcare provider to develop a dietary plan that meets your nutritional needs and minimizes symptoms.

Can Newborns be Lactose Intolerant?

While it’s very rare, some newborns can indeed be lactose intolerant. This condition is typically due to a congenital lactase deficiency, where the infant is born with a very low level or complete absence of lactase, the enzyme necessary to digest lactose.

This rare genetic disorder, also known as congenital alactasia, is inherited in an autosomal recessive pattern, meaning both parents must carry a copy of the mutation in order for a child to be affected.

In this case, the baby’s lactose intolerance is not temporary; the child will likely need to remain on a lactose-free diet their whole life.

Symptoms may present soon after birth and can include diarrhea, bloating, abdominal cramps, and failure to thrive or gain weight.

However, it’s important to note that many newborns and infants can experience temporary lactose intolerance or difficulty digesting lactose after an illness like a stomach virus, or due to a condition called developmental lactase deficiency.

This is because the lactase enzyme doesn’t reach its peak levels in the human body until after 34 weeks of gestation, so some babies, particularly those born prematurely, might not produce enough lactase for a short period of time.

These forms of lactose intolerance are usually temporary and will resolve over time.

It’s crucial to talk to a pediatrician or healthcare provider if you suspect your newborn is lactose intolerant. They can provide appropriate dietary guidance and monitor the baby’s growth and development.

Final Words on Is Lactose Intolerance Genetic?

Lactose intolerance can have a big effect on a person’s life. Symptoms can range from mild to severe, and might include belly pain, bloating, gas, nausea, and diarrhea.

These symptoms usually happen 30 minutes to 2 hours after eating or drinking something with lactose.

Understanding and managing lactose intolerance is a multifaceted task that relies on a combination of genetic testing, symptom observation, and dietary adjustments.

Though it may require some lifestyle adaptations, lactose intolerance is manageable, and individuals can lead a healthy and symptom-free life with the right care and guidance.


Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top