Poor cardiovascular fitness raises heart disease risk in teens, adults

December 20, 2005

Poor cardiorespiratory fitness affects one of five persons aged 12 to 49 years in the United States, with a disproportionate impact on adolescents, adult females and non-white minorities.

The most striking indication of the health burden of poor fitness in the U.S. population is the strong association among poor fitness, obesity and cardiovascular risk factors that is already present in adolescents and young adults, according to a study by Northwestern University researchers.

"Findings from the study have very obvious implications for the nation's obesity epidemic," said Mercedes Carnethon, lead author on the study, published in the Dec. 21 issue of the Journal of the American Medical Association.

Carnethon is assistant professor of preventive medicine at Northwestern University Feinberg School of Medicine.

This is the first large-scale study to quantify "fitness" as opposed to physical activity - physical activity is a behavior while fitness is a physiological trait.

Obesity and poor physical fitness are often related, although thin persons are not necessarily physically fit just because they are thin, Carnethon said.

Carnethon and co-researchers studied 3,100 adolescents (ages 12 to 19) and 2,200 adults (ages 20 to 49) from the cross-sectional nationally representative National Health and Nutrition Examination Survey 1999 to 2002 with no cardiovascular disease who underwent exercise treadmill testing to achieve at least 75 to 90 percent of their age-predicted maximum heart rate.

Results of the study showed that an estimated 7.5 million adolescents (34 percent) and 8.5 million adults (15 percent) have poor fitness. Prevalence of poor fitness was higher in adult females (16 percent) than males (12 percent). Non-Hispanic blacks and Mexican-Americans were less fit than non-Hispance whites.

In all age-sex groups, the greater the body mass index and waist circumference, the lower the level of fitness. In addition, total cholesterol and blood pressure were higher, and levels of HDL, or "good" cholesterol, were lower in study participants with poor versus high fitness.

"The consequences of declines in physical activity over time are now evident by the large proportion of society with poor fitness," Carnethon said.

"The correlations between poor fitness and cardiovascular disease risk factors suggest a potential trend of increasing illness and death from chronic diseases - the first sign of which is the burgeoning obesity epidemic," Carnethon said.

Historical evidence from the campaign to educate the public about the dangers of cigarette smoking indicates that education efforts, particularly among youth, can retard and reverse these negative health behaviors.

"Thus, it is plausible that a similar education campaign about the health benefits of physical activity to improve cardiorespiratory fitness, in combination with changes in policy to make environments more conducive to physical activity, could begin to reverse this serious health problem," Carnethon said.

Carnethon's collaborators on this study were Martha Gulati, M.D., assistant professor of preventive medicine and of medicine (cardiology); and Philip Greenland, M.D., Harry W. Dingman Professor of Cardiology and chair of preventive medicine, Feinberg School of Medicine.
Carnethon is supported in part by a career development award from the National Heart, Lung, and Blood Institute (5 K01 HL73249-02).

Northwestern University

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