Background It has recently come to light that the increased mortality risk in the RA population is related to increased CVD risk. The key feature explaining the increased CVD risk in this population appears to centre on inflammation.
It is reasonable to hypothesise that physical activity may reduce CVD risk in the RA population by reducing or preventing inflammation, as this has been shown to be the case by previous research in various populations. However, when investigating the impact physical activity has on inflammation in the RA population, only a small range of inflammatory markers have been assessed.
Objectives The aim of this study is to investigate if a relationship exists between energy expenditure and inflammatory markers known to be related to CVD (CRP, ESR, Fibrinogen, IL6, IL8, IL10, SAA, TNF-α and WBC) in the RA population and assess if these relationships persist after adjusting for other factors associated with high inflammatory marker levels.
Methods Analysis was conducted on 59 RA subjects, who were recruited from outpatient rheumatology clinics at the Mid Western Regional Hospitals, Limerick. All subjects wore a SenseWear Armband on the right upper arm and energy expenditure was estimated over seven consecutive days. This tool has previously been proven to be valid to estimate energy expenditure in the RA population.
Blood samples were drawn from sitting, non-fasting individuals on one occasion at the time and in the location of their initial assessment at the outpatient clinics of the Mid Western Regional Hospitals, Limerick and were analysed appropriately.
Statistical Analyses was conducted using SPSS v.18 for Microsoft Windows. Normality was assessed by use of boxplots, histograms, Quantile-Quantile plots and Kolmogorov-Smirnov statistic where appropriate. A number of variables were found to be non normally distributed and thus were transformed to a normal distribution to allow for parametric analyses.
Bivariate correlation analyses (Pearson’s correlation coefficient) were utilised to assess the strength and direction of the relationship between each of the energy expenditure variables and each of the inflammatory markers.
Using hierarchical multiple regression, it was assessed whether energy expenditure was statistically significantly contributing to the inflammatory marker levels after the effects of covariates known to impact on inflammatory markers were accounted for.
Results Bivariate correlational analysis shows that, for the total sample, energy expenditure variables showed moderate strength (r = 0.30 - 0.49) relationships with CRP, ESR, Fibrinogen, SAA and WBC with inverse relationships found.
In multiple regression analysis accounting for a number of variables which are known to impact upon inflammatory markers based on previous research, energy expenditure made a unique statistical significant (p < 0.05) contribution to CRP, ESR and SAA after controlling for covariates.
Conclusions This study shows that generally moderate strength inverse relationships exist between energy expenditure and CRP, ESR, Fibrinogen, SAA and WBC in bivariate analyses and between energy expenditure CRP, ESR and SAA after controlling for variables known to be associated with inflammatory markers. As these inflammatory markers are associated with an increased CVD risk, this study indicates that there may be a relationship between energy expenditure and cardiovascular disease in RA.
Acknowledgements Marie Tierney is supported in her postgraduate studies by scholarships sponsored by the Irish Research Council, Intel Ireland and the Central Remedial Clinic.
Disclosure of Interest None Declared
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