Does the association of habitual physical activity with the metabolic syndrome differ by level of cardiorespiratory fitness?
OBJECTIVE
Cardiovascular fitness (VO(2max)) and physical activity are both related to risk of metabolic disease. It is unclear, however, whether the metabolic effects of sedentary living are the same in fit and unfit individuals. The purpose of this study was, therefore, to describe the association between physical activity and the metabolic syndrome and to test whether fitness level modifies this relationship.


METHODS
Physical activity was measured objectively using individually calibrated heart rate against energy expenditure. VO(2max) was predicted from a submaximal exercise stress test. Fat mass and fat-free mass (FFM) were calculated using impedance biometry. A metabolic syndrome score was computed by summing the standardized values for obesity, hypertension, hyperglycemia, insulin resistance, hypertriglyceridemia, and the inverse level of HDL cholesterol and was expressed as a continuously distributed outcome. To correct for exposure measurement error, a random subsample (22% of cohort) re-attended for three repeat measurements in the year following the first assessment.


RESULTS
The relationship of VO(2max) (ml O2.kg(FFM)(-1).min(-1)) and the metabolic syndrome score was of borderline significance after adjusting for age, sex, physical activity, and measurement error (beta = -0.58, P = 0.06). The magnitude of the association between physical activity (kJ.d(-1).kg(FFM)(-1)) and the metabolic syndrome was more than three times greater than for VO(2max) (standardized beta = -1.83, P = 0.0042). VO(2max), however, modified the relationship between physical activity energy expenditure and metabolic syndrome (P = 0.036).


CONCLUSIONS
This study demonstrates a strong inverse association between physical activity and metabolic syndrome, an association that is much steeper in unfit individuals. Thus, prevention of metabolic disease may be most effective in the subset of unfit inactive people.
Franks
Paul W
PW
MRC Epidemiology Unit, Cambridge, UK. pfranks@niddk.nih.gov
Ekelund
Ulf
U
Brage
Søren
S
Wong
Man-Yu
MY
Wareham
Nicholas J
NJ
D000273:Adipose Tissue / Q000033:anatomy & histology; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002151:Calorimetry; D008076:Cholesterol, HDL / Q000097:blood; D015444:Exercise; D005080:Exercise Test; D006321:Heart / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D024821:Metabolic Syndrome / Q000503:physiopathology*; D008875:Middle Aged; D010101:Oxygen Consumption; D010809:Physical Fitness; D012044:Regression Analysis; D012137:Respiratory System / Q000503:physiopathology*
D008076:Cholesterol, HDL