Prevalent hypovitaminosis D in Crohn´s disease correlates highly with mediators of osteoimmunology

Purpose: In the context of osteoimmunology in Crohn's disease, an association was hypothesized among vitamin D and members of the TNF-α family, known as the RANK (receptor-activator of nuclear factor- κB)-RANK ligand-osteoprotegerin pathway. Methods:This was a cross-sectional study of 95 patients with Crohn’s disease (80 with long-standing disease and 15 newly diagnosed, never treated) and two control groups (healthy volunteers, n=30; and ulcerative colitis patients, n=30). Spine and hip bone mineral density was measured by dual-energy x-ray absorptiometry. Serum 25-hydroxyvitamin-D3, TNF-α, IL-6, sRANKL, osteoprotegerin levels and biochemical markers of bone turnover were analyzed. Results: The precursor metabolite, 25(OH)D3, was measured in 95 young adult CD patients (47 men, 48 women; median age 30 years). A suboptimal 25(OH)D3 level was observed in 90% of CD patients, of whom 40% had a serious deficiency. There was no significant difference in 25(OH)D3 levels between CD patients and those with ulcerative colitis. Analysis revealed an association between 25(OH)D3 deficiency and the increased biogenesis of osteoclastically-active sRANKL (p=0.014) and the proinflammatory cytokines TNF-α (p=0.015) and IL-6 (p=0.029) . CD patients with low bone mineral density had a mean 25(OH)D3 (35±18 nmol/l) in the range of serious deficiency to insufficiency, whereas mean 25(OH)D3 was higher (49±28 nmol/l) in patients with healthy bone status, although levels were still inadequate (p=0.004). The logistic model reported low levels of 25(OH)D3 to be a significant predictor of bone disease [odds ratio=2.66(6.8), p < 0.009]. In the multivariable analysis, adjusted for several confounding factors, 25(OH)D3, sRANKL, IL-6 and TNF-α were independently associated with a likelihood of bone disease [odds ratio (range): 1.02(2.75); 1.09(3.71); 1.27(6.95) respectively, p=0.001]. Conclusion: The presented findings suggest that a 25(OH)D3 deficiency accompanying an inflammatory state in CD is a high risk condition for metabolic bone disease.