Red cell distribution width, inflammatory markers and cardiorespiratory fitness: results from the National Health and Nutrition Examination Survey

Abstract

Aims: Cardiorespiratory fitness is an important predictor of cardiovascular morbidity and mortality. Both red cell distribution width (RDW) and inflammatory markers like C-reactive protein (CRP) have been shown to predict adverse outcomes in patients with heart disease.

Methods: We utilized pooled data from NHANES 1999-2004 to assess cardiorespiratory fitness in healthy adults 12-49 years old using submaximal exercise. The primary outcome was the estimated maximal oxygen uptake (VO2max). Low fitness was defined as VO2max < 20th percentile of age- and gender-based reference category.

Results: In our study, we estimated 21.2% of individuals had low fitness. Elevated RDW (>13%) was encountered in 20.4% subjects with low fitness as compared to 14.0% subjects in the control group (p < 0.001). Similarly, elevated CRP (>0.5 mg/dL) was found among 17.4% subjects with low fitness as compared to 12.4% subjects in the control group (p < 0.001). Adjusted analysis demonstrated a dose-response relationship between low cardiorespiratory fitness and increasing RDW or CRP.

Conclusion: In a large representative database of general US population, we observed a significant association between elevated RDW and elevated CRP with low cardiorespiratory fitness.

Fig. 1

Adjusted odds ratios for low cardiorespiratory fitness stratified by CRP (upper panel) or RDW categories (lower panel). The adjusted estimates were derived from multivariate logistic regression analysis after adjusting for age, gender, race, hypertension, diabetes, body mass index, hyperlipidemia, glomerular filtration rate, serum hemoglobin and serum ferritin concentration. The lowest category namely CRP < 0.5 mg/dL and RDW < 13% served as reference categories for respective comparisons.

Fig. 2

Relationship between RDW and CRP after adjusting for clinical and demographic characteristics. The entire spectrum of CRP values was divided into ten equal deciles and the median of each decile is represented on the X-axis. The Y-axis represents the odds ratio of an elevated RDW (≥ 13%) in each respective CRP decile, using the first decile (CRP: 0.01 mg/dL) as reference.

Fig. 3

Bar graph demonstrating the prevalence of low cardiorespiratory fitness among sub-groups constructed using RDW and CRP categories. For each category, the prevalence is expressed as percentage (standard error).

Fig. 4

Unadjusted (upper panel) and adjusted (lower panel) odds ratios for low cardiorespiratory fitness among sub-groups constructed using RDW and CRP categories. The adjusted estimates were derived from multivariate logistic regression analysis after adjusting for age, gender, race, hypertension, diabetes, body mass index, hyperlipidemia, glomerular filtration rate, serum hemoglobin and serum ferritin concentration. Subjects with normal CRP and normal RDW served as the reference category for this comparison.