Low cardiorespiratory fitness is an established risk factor for cardiovascular
and total mortality; however, mechanisms responsible for these associations
To test whether low fitness, estimated by short duration on a maximal
treadmill test, predicted the development of cardiovascular disease risk factors
and whether improving fitness (increase in treadmill test duration between
examinations) was associated with risk reduction.
Design, Setting, and Participants
Population-based longitudinal cohort study of men and women 18 to 30
years of age in the Coronary Artery Risk Development in Young Adults (CARDIA)
study. Participants who completed the treadmill examination according to the
Balke protocol at baseline were followed up from 1985-1986 to 2000-2001. A
subset of participants (n = 2478) repeated the exercise test in 1992-1993.
Main Outcome Measures
Incident type 2 diabetes, hypertension, the metabolic syndrome (defined
according to National Cholesterol Education Program Adult Treatment Panel
III), and hypercholesterolemia (low-density lipoprotein cholesterol ≥160
mg/dL [4.14 mmol/L]).
During the 15-year study period, the rates of incident diabetes, hypertension,
the metabolic syndrome, and hypercholesterolemia were 2.8, 13.0, 10.2, and
11.7 per 1000 person-years, respectively. After adjustment for age, race,
sex, smoking, and family history of diabetes, hypertension, or premature myocardial
infarction, participants with low fitness (<20th percentile) were 3- to
6-fold more likely to develop diabetes, hypertension, and the metabolic syndrome
than participants with high fitness (≥60th percentile), all P<.001. Adjusting for baseline body mass index diminished the strength
of these associations to 2-fold (all P<.001).
In contrast, the association between low fitness and hypercholesterolemia
was modest (hazard ratio [HR], 1.4; 95% confidence interval [CI], 1.1-1.7; P = .02) and attenuated to marginal significance after
body mass index adjustment (P = .13). Improved fitness
over 7 years was associated with a reduced risk of developing diabetes (HR,
0.4; 95% CI, 0.2-1.0; P = .04) and the metabolic
syndrome (HR, 0.5; 95% CI, 0.3-0.7; P<.001), but
the strength and significance of these associations was reduced after accounting
for changes in weight.
Poor fitness in young adults is associated with the development of cardiovascular
disease risk factors. These associations involve obesity and may be modified
by improving fitness.