Insulin resistance, high prevalence of diabetes, and cardiovascular risk in immigrant Asians. Genetic or environmental effect?

OBJECTIVES: To compare the prevalence of diabetes, hyperinsulinaemia, and associated metabolic abnormalities in immigrant Asians, Asians in India, and native white British men.
DESIGN: Case control study.
SETTING: Wythenshawe Hospital, Manchester, United Kingdom, and Maulana Azad Medical School, New Delhi, India.
SUBJECTS: Men with angiographically proved coronary artery disease; 83 British Asians, 87 white men, and 30 Indian Asians with age matched controls.
INTERVENTIONS: Fasting lipid concentrations, serum glucose, and total insulin concentrations were measured in the fasting state and one and two hours after a 75 g glucose load by mouth. All subjects had a physical examination by the same observer.
RESULTS: Asians in the United Kingdom and in India had a higher prevalence of diabetes and impaired glucose tolerance than the white British men. Patients in all three ethnic groups had higher total insulin concentrations than their controls in the fasting state and after the glucose load. British Asian and Indian Asian patients and controls had higher total insulin concentrations than the white men in the fasting state and after the glucose load. Total insulin concentrations were similar in British and Indian Asians, though fasting concentrations were higher in British Asians than Indian Asians. White men had similar cholesterol, lower triglyceride, and higher high density lipoprotein cholesterol concentrations than Asians in the United Kingdom and in India. British Asian patients had higher cholesterol concentrations and British Asian controls had higher triglyceride concentrations than the Indian Asian groups. Asian patients and controls were more active. British and Indian Asian patients had higher waist to hip ratios than controls. The waist to hip ratio was positively correlated with insulin and triglyceride concentrations and negatively correlated with the high density lipoprotein cholesterol concentration. Fasting insulin and high density lipoprotein concentrations were independent predictors of coronary artery disease in white men, whereas in British Asians the waist to hip ratio was the strongest independent predictor. In Indian Asians the waist to hip ratio and high density lipoprotein concentration were independent predictors of coronary artery disease.
CONCLUSIONS: Central obesity in the subgroups of Asians studied showed a close association with hyperinsulinaemia and the risk of coronary artery disease. A predisposition to insulin resistance and its metabolic abnormalities in this group of Asians seems to be genetically determined, environmental changes after migration having only a small additional effect.