Lactose Intolerance in Singapore

Abstract

Primary lactose intolerance has been described with varying frequency in different ethnic groups. A high incidence was described in Chinese students resident in Australia. A study was therefore undertaken on an indigenous Asian population in Singapore to establish the incidence and age of onset of lactose intolerance together with its relationship to lactose intake. Ninety-eight subjects ranging in age from 1 to 42 years were studied with lactose and glucose tolerance tests. Intestinal mucosal biopsies were assayed for lactase, sucrase, and maltase activity and examined by dissecting and light microscopy. Barium-lactose meals and xylose absorption tests also were performed. A detailed history of milk intake from birth was taken to relate the appearance or nonappearance of lactose intolerance to continued milk intake after weaning. Lactose intolerance was found to be universal after the age of 10 years. Before this there was increasing incidence of intolerance with increasing age, particularly after the age of 4 years. A secondary cause for lactase deficiency was excluded in all except 6 subjects by finding normal jejunal mucosa on dissecting and light microscopy, normal xylose absorption, and normal glucose tolerance tests. The correlation of barium-lactose meals with lactose tolerance tests and intestinal lactase activity was reasonable in adults but poor in children. It was shown that, of the tolerant children, 75% were milk drinkers and 25% were non-milk drinkers. Sixty-one per cent of the lactoseintolerant children were non-milk drinkers while 39% were milk drinkers. Intolerance appeared at an earlier age in non-milk drinkers. There is controversy on whether primary lactose intolerance is due to a genetic deficiency of intestinal lactase or whether the enzyme deficiency is adaptive. The relationship of lactose tolerance to continued milk intake after weaning found in this study would support a theory of adaptation.