Lactose intolerance

What is it

The expression “lactose intolerance” refers to a gastrointestinal syndrome triggered by the ingestion of milk (and to a certain extent also of its derivatives) and due to the inability to digest the sugar present in it, lactose precisely, which as such can not be used by the body.

This inability derives from the lack or more often from the reduced functioning of lactase, an enzyme produced by the cells of the small intestine and specifically responsible for converting lactose into the two simplest sugars that compose it (glucose and galactose), absorbable in the intestine.

What it is not

Lactose intolerance is not an allergy: at the base of its symptoms there are no immune mechanisms characteristic of allergic responses. In the specific case of milk, moreover, the true allergic reactions are directed to the proteins (and not to the sugars) present in it.

Lactose intolerance is not a real pathology: on the contrary, when it occurs after childhood it actually represents a physiological condition, linked to development, which occurs in all mammals, in whose diet milk is normally no longer present after weaning and therefore the activity of lactase undergoes a progressive reduction, genetically programmed.

In the human species, which in the course of its evolution has introduced the habit of consuming milk (that of farmed animals) in all periods of life, there is a form of persistence of lactase, linked to a genetic mutation, but its spread in the world population is extremely variable and lactose intolerance in adulthood remains the most common condition.

The prevalence of lactose intolerance varies from the very low percentages of Northern European countries, where it affects less than 10% of the population, to the very high percentages of many Asian and African countries, where over 80% of people are intolerant. In Italy, according to estimates, the problem affects 40 to 60% of the population.

Causes

The enzyme deficiency at the origin of lactose intolerance can originate from different causes and at different times in life.

The physiological reduction in lactase efficiency after childhood in the absence of the genetic mutation that keeps it active (primary hypolactasia) is by far the most common cause (present in at least 60% of the world population).

It determines a form of lactose intolerance that is characterized by extreme individual variability with respect to both the level of residual enzymatic activity and the extent of its clinical manifestations, is subject to changes in the course of life depending on the physical state (for example with pregnancy) and is also, within certain limits, sensitive to the degree of exposure to lactose.

The total absence of the enzyme lactase due to a genetic defect (congenital primary lactasia) is the rarest cause, it determines a complete inability to digest lactose that manifests itself already at birth.

The alteration of the intestinal mucosa due to intercurrent pathologies (acute enteritis, chronic inflammatory diseases, etc.) can cause, at any age, a transient lactase deficiency (secondary hypolactasia), which can regress with healing or improvement of the underlying disease.

Symptoms

The disorders caused by hypolactasia/halactasia are related to the permanence of undigested lactose in the intestine: at the level of the colon, lactose is partly metabolized by the bacteria of the intestinal flora with the production of gas (hydrogen, carbon dioxide, methane) and acid compounds, which together with unprocessed lactose tend to draw water into the intestinal lumen.

The symptoms due to these phenomena are however rather non-specific: feeling of abdominal bloating, bloating, cramping pain, diarrhea.

The most significant aspect is the temporal association between lactose intake and the onset of symptoms (which occurs within a few hours).

Diagnosis

An intolerance may reasonably be suspected on the basis of the concomitance between the consumption of foods containing lactose and the onset of symptoms or any improvement achieved by eliminating such foods from the diet.

However, some diagnostic tests can be used to confirm the hypothesis.

The most used and most reliable is the breath test for hydrogen and / or methane (the gases deriving from the fermentation of colic bacteria) which detects the increase in exhaled gases after lactose intake.

In younger children, who have difficulty performing the breath test correctly, the measurement of the pH of the stool is sometimes used, which in case of hypo / halactasia is lower (<5.5) due to the presence of acidic substances produced by intestinal bacteria.

Rarely, since it is a more invasive examination, the biopsy of the intestinal mucosa is performed to search for the enzyme.

Treatment

The most effective measure is certainly the elimination of lactose-containing substances from the diet.

In pursuing it, it is first necessary to identify one’s own individual threshold with respect to the tolerated dose of lactose and then take into account the fact that not all milk derivatives contain lactose at the same concentration (in yogurt and aged cheeses, for example, it is present in much lower quantities), that lactose is instead added in the preparation of many non-dairy foods (sausages, sauces, baked goods, confectionery, etc.) and that many drugs and supplements include it among the excipients.

If the abolition of lactose consumption is not feasible, enzyme substitutes may be used approximately one hour before the ingestion of substances containing lactose.

In some cases, especially in secondary forms liable to cure, it is possible to attempt, in parallel with the resolution of the underlying disease, a gradual reintroduction of lactose.