Background: Studies indicate that low plasma 25-hydroxyvitamin D [25(OH)D] is associated with a range of disease processes, many of which are inflammatory. However, other lipid-soluble vitamins decrease during the systemic inflammatory response, and this response may confound the interpretation of plasma 25(OH)D.
Objective: The objective was to examine whether plasma 25(OH)D concentrations change during evolution of the systemic inflammatory response.
Design: Patients (n = 33) who underwent primary knee arthroplasty had venous blood samples collected preoperatively and postoperatively (beginning 6-12 h after surgery and on each morning for 5 d) for the measurement of 25(OH) D, vitamin D-binding protein, parathyroid hormone (PTH), calcium, C-reactive protein, and albumin. A final sample was collected at 3 mo.
Results: Preoperatively, most patients were 25(OH)D deficient (<50 nmol/L) and had secondary hyperparathyroidism (PTH > 5 pmol/L). Age, sex, body mass index, season, medical history, and medication use were not associated with significant differences in preoperative plasma 25(OH)D concentrations. By day 2 there was a large increase in C-reactive protein concentrations (P < 0.001) and a significant decrease in 25(OH)D of ≈40% (P < 0.001). C-reactive protein, 25(OH)D, and calculated free 25(OH)D had not returned to preoperative concentrations by 5 d postoperatively (all P < 0.001). At 3 mo, 25(OH)D and free 25(OH)D remained significantly lower (20% and 30%, respectively; P < 0.01).
Conclusion: Plasma concentrations of 25(OH)D decrease after an inflammatory insult and therefore are unlikely to be a reliable measure of 25(OH)D status in subjects with evidence of a significant systemic inflammatory response.