Smoking and exposure to secondhand smoke have been linked to metabolic syndrome in teenagers.

Researchers said it is the first study to establish such a link in teenagers.

"The bottom line to me is: As we gear up to take on this epidemic of obesity, we cannot abandon protecting our children from secondhand smoke and smoking," said lead author Dr. Michael Weitzman, executive director of the American Academy of Pediatrics Center for Child Health Research in Rochester, N.Y.

Metabolic Syndrome

For the study, metabolic syndrome was defined as having at least three of five characteristics: a big waist, high blood pressure, high levels of blood fats called triglycerides, low levels of good cholesterol, and evidence of insulin resistance, in which the body cannot efficiently use insulin.

In the study, published Monday in the American Heart Association online journal Circulation, researchers found that 6 percent of 12- to 19-year-olds had metabolic syndrome and that the prevalence increased with exposure to tobacco smoke.

The study found that 1 percent of those unexposed to smoke developed the syndrome, 5 percent of those exposed to secondhand smoke had the disorder and 9 percent of active smokers had it.

Looking at teens who were overweight or at risk for being overweight, the effect of smoke was even more marked, with 6 percent of those not exposed to smoke developing syndrome, 20 percent of those exposed to secondhand smoke getting it and 24 percent of smokers suffering from the disorder.

"What this shows is that the percentages of kids who are at risk is vastly higher if they're overweight and they're exposed to secondhand smoke, down to very low levels," Weitzman said.

Number of Overweight Teens Has Tripled

Weitzman said it is not clear what it is about smoking that appears to make teenagers more susceptible to metabolic syndrome.

However, in adults smoking has been linked to insulin resistance, a risk factor for metabolic syndrome. Doctors also point out that smoking can lower levels of good cholesterol and raise blood pressure, two more markers for the disorder.

The researchers looked at 2,273 adolescents, using information from a Centers for Disease Control and Prevention survey. The youngsters reported their own use of tobacco. Also, the study looked at measurements of cotinine, a product of nicotine after it enters the body. Two-thirds of teens who did not smoke had cotinine levels that indicated secondhand smoke exposure.

"It's sobering," said Dr. Michael Lim, assistant professor of internal medicine in the division of cardiology at Saint Louis University School of Medicine. "What it points out is a very high-risk group of people -- young adults 12 to 19 -- who are exposed to tobacco products and sedentary."

The number of overweight teens in the United States has tripled in the past two decades.