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One-Third of U.S. Teens Out of Shape

Finding may have long-term implications for cardiovascular health

TUESDAY, Dec. 20, 2005 (HealthDay News) -- About one of every three American teens is so out of shape that even routine physical activities, such as climbing stairs, may make them winded, a new study found.

While these children may not be at immediate risk of heart disease, the study found that kids with low fitness levels already show an increased risk for cardiovascular disease in the future because their cholesterol, blood pressure and levels of obesity were higher than they were among more active teens.

The study also found that nearly 15 percent of seemingly healthy adults also had low fitness levels.

"What this really reflects is that individuals are becoming less physically active, and poor fitness is a consequence of the decline in activity," said study author Mercedes Carnethon, an assistant professor of preventive medicine at Northwestern University's Feinberg School of Medicine in Chicago.

As to why the number of out-of-shape youngsters was so much higher than in the adults studied, Carnethon said that finding wasn't unexpected because the only adults included in the study were ones who had no previous cardiovascular disease risk factors. So, any adult with high blood pressure or high cholesterol wouldn't have been included in the research. She said the group of adults in the study was considered "low risk" for cardiovascular disease and is probably fitter than the U.S. adult population as a whole. She said the findings in adolescents were probably "better representative" of the actual levels of poor fitness in the United States.

The study findings appear in the Dec. 21 issue of the Journal of the American Medical Association.

The declining levels of physical fitness in the United States have important implications for the future of America's health.

"The concern is that as these people grow into adulthood, they're going to put an increased burden on themselves and the health-care system," said Dr. Michael Gewitz, chief of pediatric cardiology at Westchester Medical Center University Hospital in Valhalla, N.Y. "Because of poor fitness, too much fat in the diet, and too many calories in the diet, the declines we've seen in morbidity and mortality in heart disease may start to be reversed by this generation."

According to the study, more than one in 10 heart attacks are caused by physical inactivity.

To assess the levels of fitness in the United States, Carnethon and her colleagues used data from the National Health and Nutrition Examination Survey collected from 1999 through 2002. This study included people between the ages of 12 and 49 from diverse racial, ethnic and socioeconomic backgrounds.

Just over 2,200 adults between 20 and 29 years old and 3,110 adolescents between 12 and 19 years old underwent treadmill testing to measure their levels of cardiorespiratory fitness.

Overall, nearly one in five of the study volunteers had low cardiorespiratory fitness. Low fitness, according to Carnethon, means the heart rate increases more than expected, or the person gets short of breath from doing normal physical activities.

Just under 14 percent of the adults had low fitness, while 33.6 percent of the teenagers did.

More females than males had low levels of fitness, and non-Hispanic blacks and Mexican-Americans were more likely to have low fitness than non-Hispanic whites, according to the study.

Low fitness was also consistently associated with being overweight or obese, according to Carnethon.

"Previous reports have measured physical activity, but cardiorespiratory fitness is a trait and a reflection of physical inactivity, so this is a more objective measurement of Americans' fitness," said Carnethon.

Carnethon said it's crucial that America's youth be educated about the consequences of physical inactivity, and start incorporating activity into everyday life.

"Park a little further away. Get off your subway a stop earlier than usual. Take the stairs," she suggested. She also said from a public health perspective, the environment needs to be made more exercise-friendly. Cities and towns need to have safe places to walk and get exercise.

"Parents need to pay attention to this issue. Healthy diets and maintaining an active lifestyle are as important as treating any other medical problem they may encounter. These set up their children's future health," said Gewitz, who recommended a minimum of three to four sessions of sustained exercise weekly for teens.

More information

Visit the U.S. Centers for Disease Control and Prevention to read their recommendations for physical activity.

SOURCES: Mercedes Carnethon, Ph.D., assistant professor, preventive medicine, Northwestern University, Feinberg School of Medicine, Chicago; Michael Gewitz, M.D., chief, pediatric cardiology, Westchester Medical Center University Hospital, Valhalla, N.Y.; Dec, 21, 2005, Journal of the American Medical Association
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