Introduction:
Low grade systemic inflammation plays a key role in the pathogenesis of atherosclerosis. There is evidence that higher cardiorespiratory fitness (CRF) is associated with lower levels of inflammatory biomarkers. However, it remains uncertain whether the negative association between CRF and inflammatory biomarkers is due to CRF itself or results from lower levels of adiposity. Moreover, adiposity, including central adiposity, has not been examined as a moderator of the association between CRF and inflammatory biomarkers in young adults.
Hypotheses:
1. Higher level of CRF will be associated with lower levels of inflammatory biomarkers after adjusting for levels of adiposity and confounders. 2. Adjusting for confounders, there will be a significant interaction effect between adiposity (BMI, waist circumference (WC)) and CRF in relation to inflammatory biomarker levels.
Methods:
A cross-sectional study was conducted in Houston, TX. A sample of 88 asymptomatic young adults aged 20-34 years without diagnosed diseases was accessed. CRF was assessed by a submaximal treadmill walking test. Adiposity was measured using BMI and WC. The inflammatory biomarkers (hs-CRP, IL-6 and TNF-α) were assayed and were log
10
-transformed. A separate multiple regression analysis was conducted with each of inflammatory biomarker as dependent variables for hypothesis one. Analysis of covariance was used for hypothesis two. Confounding variables tested were sex, ethnicity, oral contraceptive use, and education level.
Results:
Hypothesis 1: CRF was not associated with log
10
hs-CRP after adjustment for BMI (or WC) and confounders. CRF was not associated with log
10
IL-6 after adjustment for BMI and confounders. However, CRF was negatively associated with log
10
IL-6 after adjustment for WC and confounders (Model adjusted R
2
=.273,
p
< .0001;
β
= -.341, t = -1.995,
p
=.049). Hypothesis 2: CRF х BMI (or WC) interaction was not associated with log
10
hs-CRP after adjustment for confounders. CRF х BMI interaction was not associated with log
10
IL-6 after adjustment for confounders. However, CRF х WC interaction was negatively associated with log
10
IL-6 after adjustment for confounders (Model adjusted R
2
= .258,
p
< .0001; partial eta
2
=.056, F = 4.730,
p
= .033). There were no associations of CRF, adiposity, and log
10
TNF-α.
Conclusions:
In young adults, higher level of CRF is associated with lower level of IL-6 after adjustment for central adiposity and confounders. Further, there is a significant interaction between CRF and WC in relation to IL-6 after adjustment for confounders. Higher levels of CRF may play an important role for lowering some inflammatory biomarkers in central adiposity.
Association of cardiorespiratory fitness and adiposity with inflammatory biomarkers in young adults
