Saturday, March 19, 2011

Why Asian Indians are more prone to developing coronary artery disease than other groups?

By Navin Nanda, M.D.

Professor of Medicine and Director, Heart Station/Echocardiography Laboratories, University of Alabama at Birmingham, Birmingham, Alabama. Although Dr. Navin Nanda is internationally famous as an expert and innovator in echocardiography, he has also done pioneering studies in coronary artery disease in Asian Indians right from the time he was a Medical Resident at Seth G.S. Medical College and King Edward Memorial Hospital in Mumbai, India. He is the Founding President of the American Association of Cardiologists of Indian Origin and Past President of the American Association of Physicians of Indian Origin. He is currently the President of the International Society of Cardiovascular Ultrasound.

* Two facts stand out: 1) The incidence of coronary artery disease in Asian Indians is 2 to 5 times higher at all ages than Whites, African-Americans, Hispanics and other Asians. 2) It is 5 to 10 times higher in those younger than 40 years. This is not new. For example, my MD thesis from Bombay University prepared 44 years ago in 1966 was on heart attacks in patients under the age of 40 years.

* There are a host of risk factors implicated in the development of coronary artery disease in all groups. These include high blood pressure, diabetes mellitus, high blood cholesterol level, (increased “bad” or LDL cholesterol and decreased “good” or HDL cholesterol), obesity (especially abdominal), high blood triglyceride level from high saturated fat diet, sedentary life style, smoking, family history of coronary artery disease, procoagulant state (increased risk of clot formation), pollution, stressful life, to name some of them.

Many of the above factors are similar to other racial groups. However, others are more prevalent in Asian Indians. One which stands out more than others is diabetes. This is much more common in Asian Indians, has reached epidemic proportions in India and the country has the world’s largest diabetic population. Again, this is not new. For example, in 1967 we published a study from India in the New England Journal of Medicine that documented the relation of heart attacks to high blood sugar levels and showed that heart attacks triggered the development of diabetes in some of these patients. A common thread in most of the studies conducted in Asian Indians living in India as well as other parts of the world such as Africa, United Kingdom and West Indies is the presence of overt or latent (hidden) diabetes and insulin resistance. There is mounting evidence that Asian Indians may have a genetic predisposition to diabetes and coronary artery disease.

A recent survey of Asian Indians conducted at the Swami Narayan Temple in Atlanta, Georgia, showed similar findings. Asian Indians also typically have higher levels of “bad” cholesterol and lower levels of “good” or protective cholesterol. In the young (under the age of 40) Asian Indians we studied in the sixties, we found they were thin and not overweight but had high cholesterol levels, a substantial number were smokers and showed effects of pollution (“arcus senilis” or white circles in the cornea of their eyes).

Studies in Birmingham, Alabama itself have shown that Asian Indians living here have higher prevalence of smaller and denser lipoprotein (fat) particles in their blood as compared to white Americans. These particles are considered an important risk factor for the development of coronary artery disease. Asian Indians living in Birmingham have also been found to have increased platelet activation and fibrinogen in their blood as compared to whites. Both of these factors make the blood more prone to clotting and clot formation in coronary arteries result in heart attacks.

Conclusion: Higher prevalence of several risk factors most likely account for the increased incidence of coronary artery disease and heart attacks in Asian Indians.

(Republished from March, 2010 edition)