INCIDENCE OF NON-INSULIN-DEPENDENT DIABETES-MELLITUS AND ITS RISK-FACTORS IN JAPANESE-AMERICANS LIVING IN HAWAII AND LOS-ANGELES

The incidence of non-insulin-dependent diabetes mellitus (NIDDM) and i ts risk factors were analysed from data of a follow-up study conducted on Japanese-Americans living in Hawaii and Los Angeles areas known to have a high prevalence of NIDDM. There were 1144 Japanese-Americans a ged 40 years or more (mean (+/- SD) age: 60.7 +/- 10.1) available for follow-up, and who were non-diabetic based on glucose tolerance test ( GTT) results conducted at the time of the initial examination. During the study period (6.3 +/- 3.2 yr), 124 cases of NIDDM occurred with an incidence rate as high as 10.8 % or 17.2 persons per 1000 person-year s. The incidence of NIDDM was 1.25 times higher in males than in femal es, and the rate increased with age. The incidence in obese people (bo dy mass index: BMI greater than or equal to 25) was approximately twic e that in the non-obese, the rate increasing with the level of obesity . Using Cox's proportional hazards model, the risk factors for NIDDM w ere analysed after adjusting for sex and age. Significant risk factors were the serum glucose (SG) level (fasting, 1-h, 2-h), the serum immu ne-reactive insulin (IRI) level (1-h, 2-h) during GTT, BMI, serum trig lycerides, high density lipoprotein (HDL)-cholesterol, serum uric acid , diastolic blood pressure, systolic blood pressure, serum total prote in, and Delta IRI/Delta SG (0-30 min) level. In particular the hyperin sulinaemia was a significant risk factor even after adjusting for sex, age, and obesity. The incidence of NIDDM in the sub-group whose Delta IRI/Delta SG (0-30 min) level was under 0.3 was higher than that of t he over 0.8 sub-group by a factor of approximately 12. Likewise, after dividing the subjects into five sub-groups according to the fasting o r 2 h IRI level, the incidence of NIDDM was higher in the highest quin tile than in the lowest quintile sub-group by a factor of approximatel y 3 and 7, respectively. The results of the GTT of the subjects who de veloped NIDDM during the follow-up period were analysed longitudinally and compared with the results obtained 8 years before occurrence of N IDDM. An increase in the 2-h serum IRI was observed initially, followe d by an increase in the 2-h serum glucose level, preceding the appeara nce of NIDDM. In conclusion: 1. A high incidence of NIDDM is clearly o bserved in the population of Japanese-Americans, who are genetically i ndistinguishable from native Japanese; causes of this increase, from t he survey results, are suspected to include westernization of lifestyl e, particularly the reduction in the level of physical activity, conve rsion to a diet containing markedly more animal fat, simple carbohydra tes, and less complex carbohydrates. 2. In the Japanese-Americans, dim inished early insulin release to an oral glucose challenge and increas ed insulin resistance characterized by hyperinsulinaemia are suspected to be some of the important risk factors for NIDDM. Consequently, thi s study strongly suggested the possibility that the development of NID DM in Japanese persons may be influenced by environmental factors.