Context: South Asians have high rates of acute myocardial infarction (AMI) at younger ages compared with individuals from other countries but the reasons for this are unclear.
Objective: To evaluate the association of risk factors for AMI in native South Asians, especially at younger ages, compared with individuals from other countries.
Design, setting, and participants: Standardized case-control study of 1732 cases with first AMI and 2204 controls matched by age and sex from 15 medical centers in 5 South Asian countries and 10,728 cases and 12,431 controls from other countries. Individuals were recruited to the study between February 1999 and March 2003.
Main outcome measure: Association of risk factors for AMI.
Results: The mean (SD) age for first AMI was lower in South Asian countries (53.0 [11.4] years) than in other countries (58.8 [12.2] years; P<.001). Protective factors were lower in South Asian controls than in controls from other countries (moderate- or high-intensity exercise, 6.1% vs 21.6%; daily intake of fruits and vegetables, 26.5% vs 45.2%; alcohol consumption > or =once/wk, 10.7% vs 26.9%). However, some harmful factors were more common in native South Asians than in individuals from other countries (elevated apolipoprotein B(100) /apolipoprotein A-I ratio, 43.8% vs 31.8%; history of diabetes, 9.5% vs 7.2%). Similar relative associations were found in South Asians compared with individuals from other countries for the risk factors of current and former smoking, apolipoprotein B100/apolipoprotein A-I ratio for the top vs lowest tertile, waist-to-hip ratio for the top vs lowest tertile, history of hypertension, history of diabetes, psychosocial factors such as depression and stress at work or home, regular moderate- or high-intensity exercise, and daily intake of fruits and vegetables. Alcohol consumption was not found to be a risk factor for AMI in South Asians. The combined odds ratio for all 9 risk factors was similar in South Asians (123.3; 95% confidence interval [CI], 38.7-400.2] and in individuals from other countries (125.7; 95% CI, 88.5-178.4). The similarities in the odds ratios for the risk factors explained a high and similar degree of population attributable risk in both groups (85.8% [95% CI, 78.0%-93.7%] vs 88.2% [95% CI, 86.3%-89.9%], respectively). When stratified by age, South Asians had more risk factors at ages younger than 60 years. After adjusting for all 9 risk factors, the predictive probability of classifying an AMI case as being younger than 40 years was similar in individuals from South Asian countries and those from other countries.
Conclusion: The earlier age of AMI in South Asians can be largely explained by higher risk factor levels at younger ages.