Cardiovascular diseases (CVDs) account for a large proportion of deaths in people over the age of 45 years, according to background information from the authors. "Numerous risk factors for CVD, including hypertension, diabetes, and hypercholesterolemia (high cholesterol), are suspected to be influenced by fitness, and these factors may mediate the association between low fitness and mortality [death]," the authors write.
Mercedes R. Carnethon, Ph.D., from Northwestern University's Feinberg School of Medicine, Chicago, and colleagues investigated whether low fitness, estimated by short duration on an exercise treadmill test, was associated with the development of CVD risk factors and whether improving fitness was associated with risk reduction.
The participants, men and women 18 to 30 years of age, were enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study. The CARDIA study recruited 5,115 participants from four geographic areas (Birmingham, Ala., Chicago, Minneapolis, and Oakland, Calif.). Participants who completed the treadmill examination at baseline were followed up from 1985 - 1986 to 2000 - 2001. A subset of participants (n=2,478) repeated the exercise test in 1992 - 1993.
"After adjustment for age, race, sex, smoking, and family history of diabetes, hypertension or premature myocardial infarction [heart attack], participants with low fitness (less than 20th percentile) were 3- to 6- fold more likely to develop diabetes, hypertension, and the metabolic syndrome than participants with high fitness (at or above 60th percentile)," the authors write. "Improved fitness over 7 years was associated with a reduced risk of developing diabetes and the metabolic syndrome, but the strength and significance of these associations was reduced after accounting for changes in weight."
"Our findings demonstrate the importance of low cardiorespiratory fitness in young adulthood as a risk factor for developing cardiovascular comorbidities (related illnesses) in middle age," the authors write. "Previous work has demonstrated that engaging in a regular exercise program can improve fitness. If the association between fitness and CVD risk factor development is causal, and if all unfit young adults had been fit, there may have been 21 percent to 28 percent fewer cases of hypertension [high blood pressure], diabetes, and metabolic syndrome," the authors suggest. "Given the current obesity epidemic and observations of a decline in daily energy expenditure in the population, improving cardiorespiratory fitness in young men and women and developing public health policies that encourage physical activity should be important health policy goals," the authors conclude. (JAMA. 2003;290:3092-3100. Available post-embargo at JAMA.com)
Editor's Note: Work on this article was partially supported by contracts from the National Institutes of Health. Dr. Carnethon was supported in part by a career development award from the National Heart, Lung, and Blood Institute.
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JAMA