"A lot of public attention has turned from tobacco to obesity," said lead researcher Dr. Michael Weitzman, a professor of medicine at the University of Rochester School of Medicine and Dentistry. "There has never been substantial enough attention paid to the dangers of secondhand smoke to children."

Reporting in the Aug. 2 issue of Circulation, Weitzman's team looked at data on nearly 2,300 adolescents, aged 12 to 17, and found those who were overweight and had been exposed to tobacco smoke were most likely to have the metabolic syndrome -- a constellation of factors, such as high blood pressure, high blood cholesterol and high blood sugar, that increase the risk of heart attack, stroke and other cardiovascular problems.

Shorter Life Span

The new report "is the first study in any age group to show an association between secondhand smoke exposure and the metabolic syndrome," Weitzman said. "It uses a biological measure of exposure to secondhand smoke."

That marker is the blood level of cotinine, a molecule produced when the liver breaks down nicotine. Only 1.2 percent of those in the study whose cotinine levels indicated no exposure to smoke had the metabolic syndrome, while 8.7 percent of those who smoked had the syndrome and 5.4 percent of those with levels indicating exposure to secondhand smoke did.

An even greater risk was found for teenagers who were overweight or at risk of being overweight and were also exposed to smoke. Only 5.6 percent of the overweight teens who had no smoke exposure had the metabolic syndrome, compared to 23.6 percent of those who smoked and 19.6 percent of those exposed to smoke.

"So being around smokers can increase the risk by fivefold, while active smoking increases the [risk] sixfold," Weitzman said. "And the effects occur at low levels of exposure."

Because metabolic syndrome often leads to serious medical problems later in life, "the 30 percent or more of children growing up in households with a smoker are at vastly increased risk for morbidity and mortality," he said. "This is likely to be the first generation in our nation's history that will have a shorter life span than the generation that preceded it."

One of the Most Serious Causes of Disease

Some legislative action is needed to prevent children from being exposed to secondhand smoke, Weitzman said. For example, only half the states have regulations restricting smoking in childcare centers, he said.

"But what this says is that if we care about our children's health, especially in the face of the epidemic of obesity, we need to be far more stringent in getting the message out to parents and do all we can to reduce exposure to smoke in all settings." Weitzman said.

The study "adds to the body of evidence demonstrating that secondhand smoke exposure is one of the most serious causes of disease in the United States," said Matthew L. Meyers, president of the Campaign for Tobacco-Free Kids. "It is particularly disturbing because it demonstrates that exposure to smoke as a child could well have long-term heart disease consequences."

The message to parents is clear, Meyers said. "They should just not smoke in front of their kids," he stressed. "They should not smoke in the house at all."

More information: To learn more about the metabolic syndrome, check out the American Heart Association.