Low intestinal lactase activity - a 40 years perspective

Abstract

Low intestinal lactase activity (hypolactasia) was discovered in the early 1960s as a cause of lactose intolerance. Since then, it has become clear that hypolactasia in adults is a normal phenomenon in man as in other mammals. Lactase persistence is a dominant autosomal trait, enriched during thousands of years in cattle-raising populations, where continued high capacity to digest lactose might have been related to better health and more children. Hypolactasia is a cause of lactose intolerance, but it should be noted that most people with hypolactasia tolerate considerable amounts of milk products, especially when distributed throughout the day and taken with meals. Perceived intolerance to a few grams of lactose may be due to other food components or related to a general "sensitivity" of the gastrointestinal tract. Keywords: Hypolactasia, lactose intolerance, malabsorption, milk TerminologyThe original term lactase deficiency was questioned during the 70s, when it became clear that down-regulation of lactase is a normal phenomenon in man as in other mammals. Primary low intestinal lactase activity, hypolactasia and lactase restriction are terms considered more appropriate to describe the low lactase activity in adults due to down-regulation. Lactase persistence is a logical corresponding term for keeping a high intestinal lactase activity throughout life. Secondary hypolactasia means that the low intestinal lactase activity is due to damage of the small-intestinal mucosa as a result of infection, infestation, czliac disease, allergy or malnutrition. The "normal" lactase activity will then be restored when the underlying condition is cured.Lactose malabsorption or lactose maldigestion or low lactose digestion capacity means that lactose is incompletely absorbed in the small intestine, with the result that lactose passes to the large intestine. This is demonstrated through a lactose tolerance test, in which a standardised amount of lactose, usually 50 g, is given. A small blood-glucose elevation, a small blood-galactose elevation, or a small urinary galactose excretion in a lactose tolerance test with ethanol (to inhibit galactose metabolism), or an elevated breath hydrogen excretion (as a result of fermentation) are measurements used to demonstrate lactose malabsorption, which is almost always due to low intestinal lactase activity.Lactose intolerance means the experience of symptoms due to lactose malabsorption. Obviously, lactose intolerance is dosedependent, and it has been demonstrated repeatedly that hypolactasia does not always mean intolerance to normal amounts of milk products in the diet.Milk intolerance can be due to lactose intolerance, but also to milk protein allergy, and possibly related to other milk components.Pseudolactose intolerance not always means gastrointestinal symptoms related to milk in subjects with lactase persistence.