Lactose intolerance is a digestive condition that occurs when the body cannot properly digest lactose, a type of sugar found mainly in milk and dairy products. This happens when there is a shortage or complete lack of lactase, the enzyme responsible for breaking down lactose into simpler sugars for absorption. While lactose intolerance is common worldwide, its causes can vary depending on genetics, health conditions, and environmental factors. Understanding these causes can help in managing symptoms effectively and making better dietary choices.
Primary Lactase Deficiency
The most common cause of lactose intolerance is primary lactase deficiency, which usually develops gradually with age. In this condition, lactase production naturally decreases after early childhood. Many people are born with enough lactase to digest milk during infancy, but production drops as they grow older. This is a normal process in many populations and is strongly influenced by genetic background.
Genetic Factors
Genetics play a major role in determining whether someone will continue producing lactase throughout life. In populations where dairy farming and milk consumption have been common for thousands of years, such as in Northern Europe, many adults retain lactase production. In contrast, in East Asia, West Africa, and parts of South America, lactose intolerance is more prevalent because the genetic trait for continued lactase production is less common.
Secondary Lactase Deficiency
Secondary lactase deficiency occurs when the small intestine reduces lactase production due to illness, injury, or other underlying conditions. This type of lactose intolerance can appear at any age and may be temporary or permanent depending on the cause.
Digestive Disorders
- Celiac disease– Damage to the small intestine caused by gluten can reduce lactase levels until the intestine heals after gluten is removed from the diet.
- Crohn’s disease– Inflammatory bowel disease can injure the intestinal lining, leading to reduced lactase activity.
- Gastroenteritis– Severe diarrhea or stomach infections can temporarily damage the intestinal wall, resulting in short-term lactose intolerance.
Intestinal Surgery
Surgical procedures involving the small intestine, such as removal of parts of it due to cancer or other diseases, can reduce the area where lactase is produced. This can cause a permanent decrease in the ability to digest lactose.
Congenital Lactase Deficiency
In rare cases, babies are born with congenital lactase deficiency, a genetic condition where the body produces little or no lactase from birth. This condition is inherited in an autosomal recessive pattern, meaning both parents must carry the defective gene. Newborns with this condition show symptoms such as severe diarrhea and dehydration shortly after consuming milk or formula containing lactose.
Developmental Lactase Deficiency
Premature infants may experience developmental lactase deficiency because lactase production typically increases in the later stages of pregnancy. In such cases, lactose intolerance is often temporary and improves as the baby’s digestive system matures.
Environmental and Lifestyle Factors
Although genetics and medical conditions are the primary causes of lactose intolerance, certain environmental and lifestyle factors may influence lactase production and tolerance levels. These factors can make symptoms worse even in individuals who can normally handle small amounts of lactose.
Dietary Habits
People who avoid dairy products for long periods may experience reduced lactase activity, making it harder to reintroduce lactose into the diet without discomfort. This is because the body adapts to lower levels of lactose by producing less lactase.
Gut Microbiome Changes
The bacteria living in the gut help break down food, including lactose. Disruption of the gut microbiome due to antibiotics, poor diet, or illness may contribute to reduced lactose tolerance. Restoring a healthy balance of gut bacteria through probiotics and a balanced diet may help improve symptoms for some individuals.
Symptoms as a Result of the Causes
While the causes of lactose intolerance differ, they all lead to similar digestive symptoms due to undigested lactose reaching the large intestine. Bacteria in the colon ferment the lactose, producing gases and causing discomfort. Common symptoms include
- Bloating
- Abdominal cramps
- Gas and flatulence
- Diarrhea
- Nausea
Understanding Risk Factors
Some people are more likely to develop lactose intolerance due to specific risk factors, which are closely linked to the causes mentioned above. These include
- Older age – lactase production naturally declines over time.
- Ethnic background – higher prevalence in Asian, African, and Hispanic populations.
- History of intestinal diseases or surgeries.
- Premature birth.
- Family history of lactose intolerance.
Managing and Preventing Symptoms
While the underlying causes cannot always be reversed, managing symptoms is possible through dietary adjustments and treatment of any underlying conditions. Identifying the cause of lactose intolerance is essential, as secondary forms may improve once the digestive system heals from illness or injury.
Dietary Management
- Limiting or avoiding high-lactose foods such as milk, cream, and soft cheeses.
- Choosing lactose-free dairy alternatives like almond milk, soy milk, or lactose-free cow’s milk.
- Taking lactase enzyme supplements before consuming dairy to aid digestion.
Treating Underlying Conditions
For people with secondary lactose intolerance caused by celiac disease, Crohn’s disease, or infections, treating the main illness often helps restore lactase production. In such cases, lactose tolerance may gradually return.
The causes of lactose intolerance range from genetic predisposition to digestive disorders and lifestyle factors. Understanding whether it is primary, secondary, congenital, or developmental can help determine the best approach to managing the condition. By recognizing the cause and making informed dietary choices, individuals can significantly reduce discomfort and maintain a balanced, nutritious diet without unnecessary restrictions.