Summary

Lactose intolerance is a common digestive disorder affecting lactose's ability to digest. It leads to abdominal symptoms like pain, cramps, bloating, gas, diarrhea, nausea, and vomiting after consuming dairy products. 

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Overview

Lactose intolerance is a common digestive disorder that affects the ability to digest lactose, a sugar found in milk and other dairy products. It is caused by a deficiency of lactase, an enzyme produced by the small intestine that breaks down lactose into simpler sugars that can be easily absorbed into the bloodstream. The condition affects about 65% of the world's population, and certain ethnic groups, such as Asian, African, Hispanic, and Native American populations, are more susceptible. Age, family history, certain medications, and gastrointestinal surgery are some risk factors that increase the likelihood of developing lactose intolerance. There are various types of lactose intolerance, including primary, secondary, congenital, and developmental. Common symptoms include abdominal pain, cramps, bloating, gas, diarrhea, nausea, and vomiting. Several diagnostic tests are available to confirm the condition, and although there is no cure, dietary changes, lactase supplements, and probiotics can help manage the symptoms. 

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Prevalence & Risk factors

Lactose intolerance is a common condition affecting 65% of the population on average. It is rare in children younger than five years, and most often seen in adolescents and young adults. [1] Lactose intolerance is more common in certain ethnic groups, such as Asian, African, Hispanic, and Native American populations, with a prevalence of up to 80% in some of these groups. Some American Indians and East Asians even reach a prevalence of 100%. It is less common in people of European descent, with a prevalence of around 2-15%. [2, 3] 

Several risk factors can increase the likelihood of developing lactose intolerance. These include:

• Age: Lactose intolerance is more common in adults than in children, as the ability to produce lactase, the enzyme needed to digest lactose, decreases with age.
• Ethnicity: Lactose intolerance is more common among people of African, Asian, Hispanic, and Native American descent than among people of European descent.
• Family history: Lactose intolerance tends to run in families, and people with a family history of lactose intolerance are more likely to develop the condition.
• A disease affecting the small intestine: Certain medical conditions, such as Crohn's disease, celiac disease, and radiation enteritis, can damage the lining of the small intestine, reducing lactase production and increasing the risk of lactose intolerance.
• Gastrointestinal surgery: Surgery involving the stomach or intestines can also increase the risk of lactose intolerance.
• Premature birth: Premature infants may have lower lactase levels and may be at a higher risk of developing lactose intolerance.
• Certain medications: Some medications, such as antibiotics and chemotherapy drugs, can disrupt the balance of bacteria in the gut and reduce lactase production.

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Types

Lactose intolerance is caused by a deficiency of lactase, an enzyme produced by the small intestine that breaks down lactose into simpler sugars that can be easily absorbed into the bloodstream. There are four leading causes of lactase deficiency: 

• Primary Lactase Deficiency: This is the most common reason and occurs gradually as people age. Enzyme activity starts to decline in infancy, and symptoms appear in the teenage years or early adulthood. Around 70% of the population is affected by primary lactase deficiency; however, some of them are asymptomatic. [4]
• Secondary Lactase Deficiency: Some conditions affecting the small intestine can damage the intestinal lining, leading to lactase deficiency. These include intestinal infection, celiac disease, bacterial overgrowth, and Crohn's disease. [5] 
• Congenital Lactase Deficiency: This is a rare condition in which a person is born without or with deficient lactase enzyme levels. It is inherited in an autosomal recessive pattern and presents in newborns after milk ingestion. [6] 
• Developmental Lactase Deficiency: Premature infants may not have fully developed intestines to produce lactase enzymes, which results in lactase deficiency. This improves with age as the intestines mature. [7]

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Genetics

While it can be caused by a number of factors, including disease, genetics also plays a role. People with lactose intolerance often have a genetic variation that affects the expression of the lactase gene (LCT), which can result in reduced or absent activity. However, lactose intolerance can be managed through dietary changes or by taking lactase supplements. [13]

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Lactose intolerance is a complex genetic trait influenced by both genetic and environmental factors. The primary genetic factor is the LCT gene, which codes for lactase, the enzyme responsible for breaking down lactose. The expression of this gene is regulated by a nearby gene, MCM6, which controls lactase production in the small intestine. Variations in this enhancer region can affect lactase expression, and people with lactose intolerance often carry specific variants that result in reduced or absent lactase activity. In addition, other genetic factors may contribute to lactose intolerance susceptibility, such as variations in genes that affect lactase stability or lactose absorption. [14, 15] Additionally, lactase persistence, the ability to digest lactose beyond childhood, tends to decrease with age in most populations due to declining lactase activity. [16]

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Signs & Symptoms 

The signs and symptoms of lactose intolerance can vary from person to person, depending on the amount of lactose consumed and the severity of lactase deficiency. Some common symptoms include:

• Abdominal pain and cramps
• Bloating and gas
• Diarrhea
• Nausea and vomiting
• Headaches

Symptoms usually appear within 30 minutes to 2 hours after consuming dairy products. [8]

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Diagnosis

You might suspect you are lactose intolerant based on the typical gastrointestinal symptoms after consuming dairy products. Several tests can be performed to confirm the diagnosis. These include: 

• Lactose tolerance test: This test involves drinking a lactose solution and then measuring the glucose level in the blood over time. If the body cannot digest lactose, the glucose level in the blood will not rise as it should. [9] 
• Hydrogen breath test: This test involves drinking a lactose solution and then measuring the amount of hydrogen gas in the breath over time. If the body cannot digest lactose, the bacteria in the colon will ferment the lactose, producing hydrogen gas that is expelled from the breath. [10] 
• Genetic testing: Genetic testing can be used to identify gene mutations that are associated with lactose intolerance. 

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Therapy 

There is no cure for lactose intolerance, but symptoms can be managed through dietary changes and lactase supplements. In the case of secondary lactose intolerance, the underlying condition should be treated. 

Some strategies to manage the symptoms of lactose intolerance include: 

• Avoiding dairy products: People with lactose intolerance can avoid or limit dairy products or choose lactose-free or low-lactose alternatives.
• Taking lactase supplements: These supplements are available in pill or liquid form and can be taken before consuming dairy products to help digest lactose.
• Probiotics: Some studies have suggested that probiotics can improve lactose digestion and reduce symptoms in people with lactose intolerance. This is due to lactic acid bacteria that convert lactose into lactic acid instead of gas. [11]

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Prevention 

Lactose intolerance cannot be prevented, but people can reduce their risk by maintaining a healthy diet and avoiding unnecessary antibiotic use, which can disrupt the gut microbiome and lead to lactose intolerance.

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Prognosis

Lactose intolerance is a chronic condition that does not usually cause serious health problems. A diet restricted in dairy products can cause calcium and vitamin D deficiency and lead to malnutrition and low bone mass. [12]

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Recommendations

• Consume lactose-free or low-lactose alternatives, such as soy milk or almond milk.
• Gradually increase lactose intake to improve tolerance: eat smaller portions and spread them throughout the day.
• Choose aged or hard cheeses, which typically contain less lactose.
• Ensure adequate intake of calcium and other nutrients found in dairy products, either through supplements or alternative food sources.

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