Association of serum 25(OH)D with Cathepsin K levels in gingival crevicular fluid and saliva in periodontal health and disease: a cross-sectional study

This study investigates the relationship between serum vitamin D concentration and Cathepsin K (CatK) levels in gingival crevicular fluid (GCF) and saliva in both periodontal health and disease. Sixty-nine participants were categorized into four groups based on periodontal status and serum vitamin D levels: vitamin D deficient with periodontal health (n = 18), vitamin D sufficient with periodontal health (n = 18), vitamin D deficient with periodontitis (n = 17), and vitamin D sufficient with periodontitis (n = 16). Clinical periodontal parameters were recorded. CatK levels in GCF and saliva were measured using enzyme-linked immunosorbent assays. GCF and salivary CatK levels were higher in the vitamin D deficient group in both health and periodontitis, with the highest levels in the vitamin D deficient periodontitis group and the lowest in the vitamin D sufficient periodontal health group (p < 0.001). A significant negative correlation between serum vitamin D levels and both GCF and salivary CatK levels, while CatK levels positively correlated with all clinical periodontal parameters (p < 0.001). Serum vitamin D, probing pocket depth (PPD), and bleeding on probing explained 83.6% of the variation in GCF CatK levels (R² = 0.836, p < 0.001), while serum vitamin D, PPD, and gingival index accounted for 83.4% of the variation in salivary CatK levels (R² = 0.834, p < 0.001). Within the limitations of this study, vitamin D deficiency appeared to be associated with higher Cathepsin K levels in gingival crevicular fluid and saliva, particularly among individuals with periodontitis. The observed negative correlation between serum vitamin D and CatK, together with the positive associations of CatK with clinical periodontal parameters, suggests a possible link between systemic vitamin D status, local biomarker activity, and periodontal disease severity. These findings may indicate a potential role of vitamin D in periodontal host modulation, which warrants further investigation in larger, longitudinal studies.