The American Heart Association's warning last week that more children than ever are heading toward heart trouble is primarily due to the nation's obesity epidemic.

But the damage caused by too much weight isn't limited to the heart.

In its annual assessment of cardiovascular disease, the top killer in the United States, the AHA reported that about 1 million children between 12 and 19 years old, or about 4.2 percent, now have metabolic syndrome. This is an umbrella term for a host of controllable risk factors for heart disease such as abnormal blood lipids, high blood sugar, high blood pressure, and overweight or obesity.

However, those same teens may also be flirting with another health condition called insulin resistance, which is also marked by obesity. Insulin resistance is closely related to a condition called Syndrome X and to metabolic syndrome. In fact, all three terms are so similar they are often used synonymously.

The notion of Syndrome X -- a constellation of insidious symptoms characterized by the body's inability to use insulin or blood sugar -- was first proposed in 1988 by Dr. Gerald M. Reaven, an endocrinology professor at Stanford Medical School.

The bad news is that the effects of insulin resistance now appear to be under way much earlier in life than had previously been suspected. Teenagers are beginning to be seen with insulin resistance, a condition that had been relegated largely to people twice their age.

This isn't entirely a surprise in view of the widely reported epidemic of obesity among the nation's youth. But if baby fat is somehow associated with serious illness -- and research indicates this is so -- it portends a grim future for America's children.

Insulin resistance accounts for many of the interlocking serious side effects that often spin off from obesity. These include type 2 diabetes, high blood pressure, and the ravages of bad cholesterol (LDL), which can all lead to heart disease. Diabetes, which can make heart disease worse, has its own set of terrible complications, such as blindness and amputations. Adults with diabetes are two to four times more likely to have heart disease or a stroke than adults without diabetes.

The fact that insulin resistance was already at work in teenagers was reported in October by a group led by Dr. Alan Sinaiko, a professor of pediatrics at the University of Minnesota in Minneapolis.

"This study shows that insulin resistance is present at a very young age," Sinaiko said. "Even though children don't have the same degree of heart risk factors as adults, the findings suggest that insulin resistance has an early influence on what happens to people as adults."

According to the American Heart Association, more than 60 million Americans have insulin resistance. One in four of them will develop type 2 diabetes. The term "resistance" comes from the resistance of the body's cells to respond properly to even high levels of insulin. This can lead to the glucose build-up in the blood that is the hallmark of type 2 diabetes.

By monitoring teenagers every five years, Sinaiko and his colleagues found that insulin resistance was associated with higher systolic blood pressure and obesity. It was also associated with more ominous levels of cholesterol and other lipids.

The study participants were 357 healthy children recruited through the Minneapolis school system whose average age was 13 when the research began. Over the next 5.5 years, all the teens had three evaluations of their body's response to insulin: at enrollment, at age 15 and at age 19.

At the start, none of the participants had high blood pressure, and the average blood pressure for the study group was 109/55 mm Hg in 198 boys and 106/58 mm Hg in 159 girls. Recent federal guidelines set an acceptable standard of 115/75 mm Hg for adults.

By age 19, blood pressure was higher, as one would expect in older kids, but it had an extra rise for each unit of insulin resistance and another boost for each unit increase in body mass index, the standard measurement of obesity.

Sinaiko said that a key to preventing high blood pressure is to start thinking about it in childhood. "By the time people are in their 20s and 30s, a lot of the risk is already set, and we are treating the disease instead of preventing it," he noted.

Testing for insulin resistance is a complicated and expensive procedure not commonly available in doctors' offices. Doctors use a technique called the euglycemic clamp -- infusing a small amount of insulin into the blood for three hours while glucose is infused through another vein.

The link between insulin resistance and teenagers is only a new wrinkle in the campaign by some heart researchers to tie the start of coronary heart disease to dietary habits in children as young as 3.

A study of Louisiana youngsters, called the Bogalusa Heart Study and first reported in 1991 by Dr. Gerald S. Berenson and his colleagues at Tulane University School of Public Health, found grossly visible fatty streaks in the aortas of children after age 3 and in the coronary arteries beginning after age 10.

For more information on how to prevent high blood pressure, visit our prevention resources page.