Lactose Intolerance: What It Is, Types and Causes

A glass of milk, a spoonful of sour cream in borscht, a piece of cheese — and half an hour later your stomach starts rumbling and bloating. If this happens repeatedly after dairy, it may be lactose intolerance. Let's look at what this condition is and how it is confirmed.

What lactose intolerance is and how lactose is digested

Lactose is the milk sugar found in products made from animal milk: cow's, goat's, and sheep's milk. This includes milk, butter, cheese, cream, yogurt, and ice cream. It is also found in muesli with chocolate, bread, cookies and baked goods, sauces and dressings, and protein shakes.

It is broken down by the enzyme lactase. When there is too little of it, the sugar passes undigested into the large intestine: bacteria produce hydrogen, carbon dioxide, and methane, and the sugar draws water into the intestine — hence bloating, gas, and diarrhea. Lactose intolerance, or hypolactasia, is a condition caused by reduced lactase levels. It is not considered dangerous.

Symptoms: how lactose intolerance manifests

Symptoms begin a few minutes or a couple of hours after eating food with lactose:

• abdominal pain or discomfort;
• bloating and rumbling;
• gas;
• diarrhea or constipation;
• nausea, sometimes vomiting.

There can also be extraintestinal companions: headache, fatigue, joint and muscle pain. In children — chronic constipation, restlessness, and crying after eating. Without dairy, there are no symptoms.

Types: congenital, primary, and secondary lactose intolerance

Congenital lactose intolerance is an extremely rare variant in which lactase is not produced at all.

Primary, age-related, is the most common: enzyme production gradually decreases, and this can begin at any age. In Northern European residents with intolerance, it usually develops after age 20.

Secondary lactose intolerance is a consequence of another condition: inflammatory bowel diseases, celiac disease, intestinal infections, intestinal surgery, or bowel injury. In premature infants the intestine is not yet mature, and this usually resolves as they grow.

Why lactose intolerance appears with age

Lactase is controlled by the LCT gene on chromosome 2, in the 2q21 region, and nearby lies a regulatory region of the MCM6 gene that controls enzyme activity depending on age. Some people have mutations in it — at least four are known — and then lactase works throughout life.

The frequency of intolerance increases with age. At ages 2–3 years, 6 years, and 9–10 years it is: in white Americans and Northern European residents — 6–15%, in Mexican Americans — 18%, 30%, and 47%, in Southern African residents — 25%, 45%, and 60%, in Peruvian residents — 30–55%, 90%, and above 90%. Lactose intolerance occurs in 50–80% of Ashkenazi Jews. In Russia the frequency depends on the region; in the North, up to 35% of residents may be predisposed. At the same time, 81% of adult Japanese tolerate up to 200 milliliters of milk without symptoms.

How lactose intolerance is diagnosed

First the doctor checks whether the complaints are related to dairy: they may suggest a trial elimination of lactose-containing products, order blood tests, and a hydrogen breath test.

Hydrogen test: the person takes 50 g of lactose, then hydrogen in the breath is measured. The diagnosis is confirmed if hydrogen is above 20 ppm and blood glucose has risen by less than 20 milligrams per deciliter (1 millimole per liter). If the complaints are severe and do not resolve, gastroscopy with a biopsy of a tiny piece of small intestinal mucosa may be needed.

How it differs from milk allergy and when to see a doctor

Milk allergy is a reaction to milk protein, and it can be life-threatening: difficulty breathing, itchy skin, swelling of the lips, face, and eyes. Lactose intolerance is about the enzyme and digestion, not immunity.

See a doctor if symptoms return after eating; unusual changes in stool persist for three weeks; there is blood in the stool for three weeks; bloating and discomfort do not subside for three weeks; weight is lost without effort. You should not remove dairy from your diet or a child's diet without advice from a doctor or nutrition specialist.

Lactose intolerance itself is not a reason to call an ambulance. 103 or 112 — if the lips, mouth, throat, or tongue suddenly swell; if breathing is rapid or labored, there are wheezes, or a feeling of suffocation; if swallowing is difficult; if the skin, tongue, or lips are blue, gray, or pale; if the person is suddenly disoriented, drowsy, or dizzy; if they have lost consciousness and do not wake up. This may be a severe allergic reaction.

This material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer