Caused by deficient activity of lactase, which is an intestinal enzyme that breaks down lactose; lactose is a carbohydrate found in dairy products.
Lactose intolerance prevalence worldwide is estimated to be more than 65%.
Prevalence varies widely according to population: ~30% in Europe, ~50% in the United States, ~70% in Asian countries, and nearly 100% in Africa; variability likely reflects genetic adaptations in populations heavily reliant on dairy products).
SYMPTOMS
Vary according to the extent of the deficiency and other factors.
- Abdominal cramping
- Bloating/gas
- Diarrhea
- Nausea
CAUSES
We can break down the causes of lactase deficiency into three groups:
Congenital lactase deficiency is a rare autosomal recessive disorder with deficient enzyme activity from birth.
Primary lactose intolerance (adult-type lactase deficiency) is the common condition resulting from downregulated lactase gene expression over the course of normal human development (also an autosomal recessive trait).
Secondary lactase deficiency is transient state due to intestinal damage caused by infections, food allergies, etc. In these cases, the intestinal villi will appear damaged, whereas the intestinal villi in primary lactose intolerance appear normal.
PATHOPHYSIOLOGY
In the presence of lactase, lactose is broken down to form galactose and glucose, which are absorbed into the blood stream.
However, in the absence of lactase, the lactose remains in the intestines with the following outcomes:
- The undigested lactose produces pulls water into the intestines, causing osmotic diarrhea.
- Bacterial enzymes ferment lactose and produce short-chain fatty acids and gas with abdominal pain, bloating, and flatulence.
DIAGNOSIS
We often use a hydrogen breath test to diagnose lactose intolerance. To administer the test, we collect baseline levels of hydrogen in the breath, then administer a lactose solution.
In the setting of lactase deficiency, hydrogen production will increase from bacterial fermentation in the colon.
If hydrogen increases more than 20 ppm (parts per million) above baseline, the patient has lactase deficiency.
We can also use blood glucose tests, DNA tests, and stool acidity tests to determine lactase status.
It is recommended that patients reduce consumption of lactose-rich foods; patients may need to experiment to find out how much lactose they can "tolerate," as this varies by person.
Be aware that lactose intolerance is different from "milk allergy," which is an immune-mediated reaction to cow's milk proteins.
TREATMENT
Dietary - avoid dairy products.
Use lactase supplements.
