In healthy people, hydrolytic activity of lactase (E.C.3.2.1.2.3) present in brush border of enterocytes is characterised by great diversity determined among other things by age. It is relatively high in perinatal period and decreases by two- or four-times during 2-12 month of life. In some cases, the activity of this enzyme in subsequent years continues to decrease gradually, which results in a considerable impairment of tolerance to lactose found in food. This drop in lactose activity is genetically conditioned (Primary Hypolactasia, Adult-type Hypolactasia) and it is related to both the process of lactase gene transcription and post-translation mechanisms. The study is devoted to immediate consequences of fermentation of not absorbed lactose, as well as to delayed consequences of diet limitations and possible effects of long-lasting activity of potentially-pathogenic fermentation products on the mucous membrane of large bowel. Various methods of treating the states of Primary Hypolactasia were also discussed in the present work.

Keywords: adult-type hypolactasia, Epidemiology, Genetics, Hydrogen, colonic flora, Lactase