Lactose malabsorption and small-intestinal lactase in normal Chinese children

Lactase deficiency and lactose intolerance in a multiracial Asian population in Malaysia

Background and Aims

There have been few reports on lactase deficiency (LD) and lactose intolerance (LI) in Malaysia, which has a peculiar mix of three distinct major Asian races-Malay, Chinese, and Indian. The aim of this study was to determine the prevalence of LD and LI in a young multiethnic Malaysian population.

Methods

Lactase activity was measured with a ¹³CO₂ lactose breath test using an infrared spectrometer. Each subject took 25 g of lactose naturally enriched in ¹³CO₂ together with 250 mL of water after an overnight fast. Breath samples were collected at baseline and at 15-min intervals for 180 min. Subjects were asked to report gastrointestinal (GI) symptoms following ingestion of the lactose test meal.

Results

Of the 248 subjects tested, 216 (87.1%) were lactase deficient. We found no significant differences in the presentation of LD between gender and races. LD was found in 87.5% of males and 86.8% of females (P = 0.975) and in different races: Chinese (88.5%) versus Malay (83.1%) (P = 0.399), Indian (90.5%) versus Malay (P = 0.295), and Chinese versus Indian (P = 0.902). LI was diagnosed in only 49 (19.8%) subjects; 35 patients had diarrhea, while the remainder had at least two other GI symptoms after the lactose meal.

Conclusion

The prevalence of LD was high in all three major ethnic groups-Malays, Chinese, and Indians. Ironically, the prevalence of LI was low overall.

Genetics and epidemiology of adult-type hypolactasia

The prevalence of adult-type hypolactasia varies from less than 5% to almost 100% between different populations of the world. The lowest prevalence has been found in northwestern Europe, around the North Sea, and the highest prevalence in the Far East. The reason for the variation is that selective (primary) hypolactasia is genetically determined by an autosomal recessive single gene. It is assumed that thousands of years ago all people had hypolactasia in the same way as most mammals do today. At that time in cultures where milk consumption was started after childhood, lactase persistence had a selective advantage. Those people with lactase persistence were healthier and had more children than people with hypolactasia, and the frequency of the lactase persistence gene started to increase. The present prevalence of hypolactasia can be explained fairly well by this culture historical hypothesis. This article reviews the evidence for the inheritance of adult-type hypolactasia and the occurrence of hypolactasia in different countries and populations of the world.

The status of lactose absorption in Hong Kong Chinese children

Lactose malabsorption was investigated in 169 Chinese children aged between two and 16 years using the breath hydrogen test. The challenge was either lactose solution (1 g/kg) or cow's milk (10 ml/kg). Overall, 68% of the children showed a significant increase in breath hydrogen following the lactose challenge while only 17% showed an increase after the cow's milk challenge and 13% after both challenges. The number of malabsorbers increased significantly (p less than 0.001) with age and no associated gastrointestinal symptoms or signs were found in any of the children following the challenges, suggesting a gradual and partial loss of intestinal lactase activity. We conclude that the prevalence of lactose malabsorption in Hong Kong children is very high using the standard lactose tolerance test but when a more realistic amount of lactose and a natural medium such as a glass of milk is used as the challenge, the number of malabsorbers becomes small and clinically insignificant.

Late-onset hypolactasia in Hong Kong school children

Three hundred and twenty Chinese school children aged between 6 and 19 years from six schools in Hong Kong were tested for their lactose digestion status. After an overnight fast, the children were challenged with cow's milk, 5 ml/kg bodyweight (i.e. lactose approximately 0.25 g/kg). Malabsorption was assessed by measuring hydrogen concentration from end-expiratory breath samples taken in duplicate before and at 90 and 180 minutes after the challenge. On average, 10% of the children showed an increase in breath hydrogen excretion within 3 h after the challenge, indicating malabsorption of lactose. None of the children complained of gastro-intestinal symptoms or showed any clinical sign of intolerance to the milk. The number of malabsorbers increased significantly (p less than 0.001) with age, starting at about 3% at the age of 8 and reaching about 27% at the age of 18 years. The sharpest rise occurred between 14 and 15 years. It is concluded that, despite the high prevalence of hypolactasia, Hong Kong Chinese children can consume normal amounts of milk without developing any untoward clinical symptom or sign.