Lactose intolerance is common in Thai adults who ingest cow’s milk but its incidence has not been clearly defined. The authors evaluated 45 volunteers (15 males, 35 females), aged 21-31 yrs old, who drank one 240-ml box of milk daily. A Lactose tolerance test was performed using a breath- hydrogen test (BHT) after oral intake of 25 g of lactose dissolved in 250 ml of water. The presence of gastrointestinal symptoms of lactose intolerance, flatulence, abdominal pain and diarrhea, were recorded. Twenty-one subjects (47%) were categorized as lactose malabsorbers and intolerant, two subjects (4%) were malabsorbers but tolerant, and 22 of 45 (49%) were absorbers and tolerant. The incidence of lactose malabsorption was, thus, 51%;
symptoms of intolerance were found in 21 of the 23 malabsorbers, making the incidence of lactose intolerance
47%. In the lactose malabsorbant and intolerant group, the more breath-hydrogen (H2) the more symptoms observed. All subjects who had a negative breath-H2 test had no symptoms. The breath-H2 test should be used as a standard method to evaluate lactose absorption and lactose tolerance. The incidence of lactose intolerance has decreased from the past and the symptoms are not so severe that the people limit the consumption of milk since it is a major source of food containing good quality of protein and calcium.

Keywords: Lactose malabsorber, Lactose absorber, Lactose intolerance, Lactose tolerance, Lactase, Breathhydrogen
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