Association between 25-OH-vitamin D and C-reactive protein as a marker of inflammation and cardiovascular risk in clinical practice.

Background C-reactive protein is an acute phase response marker and, in an epidemiological context, a predictor of cardiovascular risk. 25-Hydroxy-vitamin D is the best indicator for vitamin D status, but it can be altered by the presence of acute phase response. Our aim was to evaluate the association between serum concentrations of 25-hydroxy-vitamin D and C-reactive protein to assist the interpretation of vitamin D status in a clinical context. Methods We evaluated retrospectively 5076 patients (n = 4087 women) assessed for 25-hydroxy-vitamin D and C-reactive protein simultaneously. Subjects were classified according to the origin as hospitalized patients (n = 410) and outpatients (n = 4666). Outpatients included patients from specialized (n = 3943) and primary (n = 723) care. Serum 25-hydroxy-vitamin D was determined by using liquid chromatography and serum C-reactive protein by using immunoturbidimetry. Results Concentrations of 25-hydroxy-vitamin D and C-reactive protein were significantly different between hospitalized subjects and outpatients but not for specialized and primary care settings. Serum concentrations of 25-hydroxy-vitamin D decreased as C-reactive protein increased. Hospitalized patients with C-reactive protein concentrations >30 mg/L showed a significant reduction of 25-hydroxy-vitamin D. In outpatients with C-reactive protein within the reference range (<= 10 mg/L), C-reactive protein concentrations were not significantly different for serum 25-hydroxy-vitamin D concentrations >37.5 nmol/L. Conclusions Our data question the reliability and usefulness of assessing 25-hydroxy-vitamin D status as a biomarker of nutritional status in patients displaying acute phase response, especially at concentrations of C-reactive protein >30 mg/L. In addition, the present study shows that in subjects displaying C-reactive protein values within the reference range, serum concentrations of 25-hydroxy-vitamin D >37.5 nmol/L were not associated with lower concentrations of cardiovascular risk (as assessed by C-reactive protein concentrations).