- The first publication of an excess burden of CAD (coronary artery disease) came from Singapore in 1959, based on 9568 post-mortem studies (including 655 Indian men and 159 Indian women).1 This first report showed that CAD rates among Indians in Singapore was seven times higher than Chinese. CAD accounted for 50% of all heart disease cases in Indian men but only10-20% in Chinese men.1
- A second publication in 1960 further corroborated the excess burden of CAD in Indians. Compared to Chinese or Malay (the dominant populations), the CAD death rate was 20 times higher among Indian Muslims and 10 ten times higher among Indian Hindus.2
- This report also alerted to the premature death from CAD among Indians. The average age of death was 44 years among Indians compared to 52 among Chinese and 51 for Europids.2
- Singapore, which has provided extensive research data for the past 50 years, is widely recognized as a population laboratory to explore ethnic variations in the epidemiologic transition.3 Singapore is a small multiethnic stable island-state with rapid economic development and similar ethnic composition of Chinese, Malays, South Asians, and Europeans allowing comparison in a roughly controlled environment. Indians make up 7% of Singapore’s population; of these, 80% originate from South India and Sri Lanka.
- In Singapore, where all heart attack occurrences in the country are systematically entered in the registry, the incidence of heart attacks has been tracked closely for the past several decades.4 The analysis of these extensive data showed a doubling of the death rate from heart attack nationwide till 1990 followed by decline.5, 6 This increase in heart disease was attributed to changes in lifestyle (higher rates of smoking, greater obesity, more fattening diets, and a more sedentary lifestyle), since this is a very short period for any genetic changes to occur.7
- As a result of health programs and modernization, a decline in annual CAD mortality was observed from 1991 to 1999. Strikingly, the difference in CAD incidence or mortality between Chinese and Indians in Singapore has not narrowed.4, 6, 8 Several studies over the past 5 decades have shown that Indian men and women are three to four times more likely to have heart attacks and die from it than Chinese Singaporeans.4, 7, 9-12 The difference in incidence of CAD in the year 2000 is given in Figure 031.7
- After all, it is highly unlikely that Indians gained twice the weight as Chinese, smoked twice as many more cigarettes, and ate twice as much more fat. The data shows that the increase in risk factor levels from adverse changes in lifestyle has been similar in Chinese and Indians. These data suggest fairly convincingly that harmful changes in lifestyle related to affluence, urbanization, and sedentary living are magnified in Indians compared to others due to genetically inherited risk factors.5, 13
- All of the traditional risk factors for CAD were found to play important but varying roles in the ethnic groups in Singapore.13 Several studies have shown that the high rates of heart disease in Indians in Singapore is not due to differences in cigarette smoking, blood pressure, physical activity, LDL or HDL cholesterol, triglyceride, alcohol consumption or vitamin A and E levels.14
- Indians in Singapore have lower levels of vitamin C, which may be due partly to not consuming fresh fruits and vegetables and partly to the destruction of this vitamin from prolonged cooking at high temperatures as is customary in the Indian cuisine.5, 15
- Asian Indians in this country has been shown to have consistently lower levels of coenzyme Q10, which may be contributing to the high rates of muscle symptoms with statins observed in this population.16
- Indians have higher levels of emerging risk factors like homocysteine, plasminogen activator inhibitor, and especially lipoprotein(a) (Lp(a)). Median Lp(a) levels are significantly higher in Asian Indians (12 mg/dl) compared to Chinese (10 mg/dl) and Malays (8 mg/dl).17
- Racial differences in plasma Lp(a) levels are present and expressed at birth. Expression of the racial profile of Lp(a) at birth was studied in the cord blood of 542 male and 468 female newborns from three ethnic groups of Singapore (see Figure 004 in Double Jeopardy). Lp(a) levels in newborns were found to be independent of the infant’s birth weight and sex but were significantly influenced by race.
- Indian newborns had significantly higher plasma levels of Lp(a) and Chinese newborns had the lowest Lp(a) levels at birth.18 The ranking of Lp(a) levels at birth was concordant with the relative coronary mortality rates for the respective adult populations of Singapore for the past 50 years.18
- The multiplicative effects of emerging and traditional risk factors on a background of genetic susceptibility mediated by Lp(a) offers a plausible explanation of excess burden of CAD among Indians in Singapore.19, 20
1. Danarag TJ, Acker M, Danaraj W, Ong W, Yam T. Ethnic group differences in coronary heart disease in Singapore: an analysis of necropsy records. Am Heart J. 1959;58:516-526.
2. Muir C S. Coronary heart disease in seven racial groups in Singapore. Br Heart J. Jan 1960;22:45-53.
3. Ounpuu S, Yusuf S. Singapore and coronary heart disease: a population laboratory to explore ethnic variations in the epidemiologic transition. Eur Heart J. Jan 2003;24(2):127-129.
4. Mak KH, Chia KS, Kark JD, et al. Ethnic differences in acute myocardial infarction in Singapore. Eur Heart J. 2003;24(2):151-160.
5. Hughes K. Coronary artery disease in Indians in Singapore. In: Sethi K, ed. Coronary artery disease in Indians – A Global perspective. Mumbai: Cardiological Society of India; 1998:56-62.
6. Hughes K. Trends in mortality from ischaemic heart disease in Singapore, 1959 to 1983. Int J Epidemiol. 1986;15(1):44-50.
7. Heng DM, Lee J, Chew SK, Tan BY, Hughes K, Chia KS. Incidence of ischaemic heart disease and stroke in Chinese, Malays and Indians in Singapore: Singapore Cardiovascular Cohort Study. Ann Acad Med Singapore. 2000;29(2):231-236.
8. Hughes K, Yeo PP, Lun KC, et al. Cardiovascular diseases in Chinese, Malays, and Indians in Singapore. Differences in risk factor levels. J Epidemiol Community Health. 1990;44(1):24-35.
9. Enas EA. How to Beat the Heart Disease Epidemic among South Asians: A Prevention and Management Guide for Asian Indians and their Doctors. Downers Grove: Advanced Heart Lipid Clinic USA; 2010.
10. Rambihar VS, Rambihar SP. Heart disease and South Asians 50 years later: a time for change. Heart. Jul 2010;96(14):1168.
11. Rambihar VS, Rambihar SP. Race, ethnicity, and heart disease: a challenge for cardiology for the 21st century. Am Heart J. Jan 2010;159(1):1-14.
12. Mak KH, Chia KS, Kark JD, et al. Ethnic differences in acute myocardial infarction in Singapore. Eur Heart J. Jan 2003;24(2):151-160.
13. Lee J, Heng D, Chia KS, Chew SK, Tan BY, Hughes K. Risk factors and incident coronary heart disease in Chinese, Malay and Asian Indian males: the Singapore Cardiovascular Cohort Study. Int J Epidemiol. 2001;30(5):983-988.
14. Hughes K, Yeo PP, Lun KC, et al. Ischaemic heart disease and its risk factors in Singapore in comparison with other countries. Ann Acad Med Singapore. 1989;18(3):245-249.
15. Hughes K, Yeo PP, Lun KC, et al. Ischaemic heart disease and its risk factors in Singapore in comparison with other countries. Ann Acad Med Singapore. 1989;18(3):245-249.
16. Hughes K, Lee BL, Feng X, Lee J, Ong CN. Coenzyme Q10 and differences in coronary heart disease risk in Asian Indians and Chinese. Free Radic Biol Med. Jan 15 2002;32(2):132-138.
17. Wong MS, Chew WL, Aw TC. Serum lipoprotein(A) profiles in a Singaporean population. Pathology. Aug 1999;31(3):225-229.
18. Low PS, Heng CK, Saha N, Tay JS. Racial variation of cord plasma lipoprotein(a) levels in relation to coronary risk level: a study in three ethnic groups in Singapore. Pediatr Res. 1996;40(5):718-722.
19. Enas EA, Singh V, Munjal YP, Bhandari S, Yadave RD, Manchanda SC. Reducing the burden of coronary artery disease in India: challenges and opportunities. Indian Heart J. Mar-Apr 2008;60(2):161-175.
20. Yeo KK, Tai BC, Heng D, et al. Ethnicity modifies the association between diabetes mellitus and ischaemic heart disease in Chinese, Malays and Asian Indians living in Singapore. Diabetologia. Dec 2006;49(12):2866-2873.