Introduction

Type 2 diabetes, or non insulin-dependent diabetes mellitus (NIDDM), is less frequent in Japan than in the United States. It is a heritable disease as demonstrated by a very high concordance rate (95%) in Japanese and European identical twins (Kuzuya et al., 1987; Barnett et al., 1981). However, it is also well known that many environmental factors contribute to the pathogenesis of NIDDM. Thus, analyses of both genetic and environmental factors and their interactions may be expected to promote further understanding of the pathogenesis of diabetes and provide knowledge useful to its prevention.

This paper presents epidemiological data about type 2 diabetes in Japanese in Japan as compared to Japanese migrants to the United States and Brazil. Since the modernisation of life style that is occurring in Japan may have a strong influence upon the incidence of diabetes there, a study of Japanese migrants who have already experienced these changes elsewhere associated with westernisation throughout their life may show the rates for diabetes to be expected when Japan is fully westernised. This paper also describes the difficulties encountered in a study of relatives in Japan of Seattle Nisei (second generation Japanese- American) who had been studied by Fujimoto et al. (1987a,b).

Epidemiology of diabetes mellitus in Japan

There have been few population-based studies on prevalence and incidence of diabetes mellitus in Japan. Since government health insurance covers almost all of the Japanese population, statistics of the Ministry of Health and Welfare can be used to estimate the prevalence of diabetes (Health and Welfare Statistics Association, 1989).