Studies on the etiology of milk intolerance in Japanese adults.

1. The incidence of milk intolerance is approximately 19% in Japanese adults when 200 ml of milk is given. However, a much greater incidence was assumed when considered under the criteria of Western standard. 2. The lactase activity was significantly greater in milk drinkers than non-drinkers. And, internationally, the active is higher in those nationalities whose milk consumption is greater. 3. Lactase is an adaptive enzyme and rather easily induced by lactose load feeding in animals. From the data of our own and of the literature, it was further confirmed that environmental factors play a more important role than genetic factors in the etio-pathogenesis of milk intolerance.