Lactose intolerance is the inability to digest lactose, a sugar found in dairy products, due to a deficiency of the enzyme lactase. This condition affects approximately 65% of the global population with varying prevalence among different ethnic groups.
Lactose is made up of two simple sugars: glucose and galactose.
Signs and Symptoms
The primary symptoms of lactose intolerance include abdominal pain, bloating, diarrhoea, flatulence, and nausea, typically occurring 30 to 120 minutes after consuming lactose-containing foods. The severity of symptoms depends on the amount of lactose ingested and individual tolerance levels. Unlike milk allergy, lactose intolerance does not cause immune reactions such as itching, hives, or anaphylaxis.
Causes
Lactose intolerance results from a deficiency of lactase, an enzyme produced in the small intestine that breaks down lactose into glucose and galactose for absorption. This deficiency can be genetic or acquired. There are four types of lactose intolerance:
Primary Lactose Intolerance: Common and genetically determined, it occurs as lactase production decreases after childhood.
Secondary Lactose Intolerance: Caused by injury to the small intestine due to infections, celiac disease, Crohn's disease, or other conditions.
Developmental Lactose Intolerance: Occurs in premature infants but usually improves over time.
Congenital Lactose Intolerance: A rare genetic disorder present from birth, characterised by a complete lack of lactase.
An estimate of the percentage of adults that can digest lactose in the indigenous population of the Old World.
Diagnosis
Diagnosis of lactose intolerance involves several steps to confirm the condition:
Hydrogen Breath Test: Measures hydrogen levels in breath after ingesting lactose. High levels indicate lactose intolerance.
Lactose Tolerance Test: Monitors blood glucose levels after lactose ingestion. A flat glucose rise suggests lactose malabsorption.
Stool Acidity Test: Used for infants, it tests stool acidity after lactose ingestion. Acidic stools indicate intolerance.
Intestinal Biopsy: Confirms lactase deficiency through tissue samples.
Genetic Testing: Identifies specific mutations associated with primary lactose intolerance.
Management
Management primarily involves dietary adjustments and supplements:
Dietary Avoidance: Limiting lactose intake to avoid symptoms. Individuals vary in their tolerance levels, and many can consume small amounts of lactose without significant issues.
Lactase Supplements: Over-the-counter lactase enzyme supplements can help digest lactose when consuming dairy products.
Lactose-Free Products: Use of lactose-free milk and dairy products as substitutes.
Calcium Intake: Ensuring adequate calcium intake through non-dairy sources or supplements to maintain bone health.
Epidemiology
Lactose intolerance varies significantly across populations:
High Prevalence: East Asian, West African, Jewish, and Arab descent populations, with up to 90-100% affected.
Low Prevalence: Northern European populations, with about 5% affected due to historical dairy farming and genetic adaptations.
Historical Context
Lactase persistence, the ability to digest lactose into adulthood, evolved in populations with a history of dairy farming, such as in Europe, Scandinavia, and parts of Africa. This genetic adaptation occurred independently in various regions due to the benefits of digesting milk from domesticated animals. The understanding of lactose intolerance has evolved, recognising it as common globally rather than an anomaly limited to certain populations.
Other Animals
Most mammals, including humans, typically lose the ability to produce lactase after weaning. This natural decline in lactase production is also observed in other mammals, driven by genetic and epigenetic factors such as DNA methylation.
What enzyme is deficient in individuals with lactose intolerance?
Which symptom is NOT typically associated with lactose intolerance?
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