At first, the 36-year-old South Asian immigrant didn't seem a typical candidate for a heart attack. He was lean, a nonsmoker and had healthy blood pressure. Only his cholesterol levels hovered just above normal. But when his chest pain lasted for an hour, he headed for the emergency room.

Good thing. Not only was he having a major heart attack, which doctors treated with clot-busting drugs, but he had three badly blocked arteries that required bypass surgery and he was diagnosed with type 2 diabetes.

So how does a young guy seemingly in good health suddenly become such a medical train wreck?

Add ethnicity to the list of risk factors for heart disease, type 2 diabetes and the metabolic syndrome -- a cluster of problems including high blood pressure, elevated blood sugar and too many blood fats. This case was reported in 2006 in the journal Circulation by an international team of doctors who hoped to alert colleagues to watch for similar patients who could be slipping under the medical radar.

An estimated 3 million South Asian immigrants now live in the United States and Canada. Studies suggest that this diverse group -- with family roots in India, Pakistan, Nepal, Sri Lanka and Bangladesh -- is three to five times more likely to have a heart attack or to die from heart disease compared with other populations -- despite the fact that many of them are at a healthy weight by Western standards.

Research hints at other ethnic differences. African-Americans seem to be at much greater risk of high blood pressure compared with other groups. The Pima tribe of Arizona and other Native American peoples have soaring rates of type 2 diabetes, a condition that also is two to five times more common in Hispanics than in non-Hispanic whites.

The culprit appears to be the way fat is accumulated. South Asians, as with some other ethnic groups, tend to pile on more fat around the middle even though they are not overweight by Western standards. Differences such as these are prompting some international health groups to adjust their screening tools by ethnicity.

Take the well-known body mass index, or BMI. It uses height and weight to gauge risk of weight-related complications. (BMI is calculated by dividing a person's weight in kilograms by height in meters squared.)

The National Heart, Lung, and Blood Institute sets a BMI of 18.5 to 24.9 as healthy; 25 to 29.9 as overweight; and 30 and higher as obese.

But studies suggest that the BMI cutoffs that estimate weight-related risks for Caucasians of European heritage may sometimes give a false sense of security to people with Asian ancestry and cause unnecessary concern to those with African roots.

So in recent years, the World Health Organization has lowered the cutoff for obesity for Asians from a BMI of 30 to 25.

The International Diabetes Federation (IDF) has also set ethnic-based cutoffs for waist circumference. For Americans, the IDF says waistlines of 40 inches or larger are cause for concern in men; 35 inches or larger in women.

But for European and Middle Eastern residents, the IDF has set waist circumference cutoffs of 37 inches for men; 32 for women. Men from China as well as Central and South America are advised by the IDF to keep their waist sizes less than 35 inches.

"I definitely pay attention to the race of my patients," notes Dipanjan Banerjee, a cardiovascular fellow at Stanford University and co-author of a recent report in the International Journal of Obesity on using ethnic-specific criteria to improve the diagnosis of the metabolic syndrome. "If I see a South Asian man who is young with chest pain, I know that the probability of his having heart disease is higher than a Caucasian man the same age. So I do tend to be more aggressive with those patients."

But Banerjee also notes that taking into account the ethnicity of patients gets into some thorny questions.

Race is generally self-reported and may reflect a person's identity more than genetic makeup. "How do you determine who is actually African or Indian?" he asks. "What we are trying to capture with these crude racial classifications is a greater understanding of risk factors."

He envisions the day when doctors will instead sample genetic profiles that will be far more accurate in assessing risk than skin color or country of origin. "We are moving toward genetic therapy for cardiovascular disease and other medical conditions," he says. "That is what we are all trying to do."

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