Low serum and bone vitamin K status in patients with longstanding Crohn's disease: Another pathogenetic factor of osteoporosis in Crohn's disease?

Background-A high prevalence of osteoporosis is reported in Crohn's disease . The pathogenesis is not completely understood but is probably multifactor ial. Longstanding Crohn's disease is associated with a deficiency of fat so luble vitamins, among them vitamin K. Vitamin K is a cofactor in the carbox ylation of osteocalcin, a protein essential for calcium binding to bone. A high level of circulating uncarboxylated osteocalcin is a sensitive marker of vitamin K deficiency. Aims-To determine serum and bone vitamin K status in patients with Crohn's disease and to elucidate its relationship with bone mineral density. Methods-Bone mineral density was measured in 32 patients with longstanding Crohn's disease and small bowel involvement, currently in remission, and re ceiving less than 5 mg of prednisolone daily. Serum levels of vitamins D an d K, triglycerides, and total immunoreactive osteocalcin, as well as uncarb oxylated osteocalcin ("free" osteocalcin) were determined. The hydroxyapati te binding capacity of osteocalcin was calculated. Data were compared with an age and sex matched control population. Results-Serum vitamin K levels of CD patients were significantly decreased compared with normal controls (p<0.01). "Free" osteocalcin was higher and h ydroxyapatite binding capacity of circulating osteocalcin was lower than in matched controls (p<0.05 and p<0.001, respectively), indicating a low bone vitamin K status in Crohn's disease. In patients, an inverse correlation w as found between "free" osteocalcin and lumbar spine bone mineral density ( r=-0.375, p<0.05) and between "free" osteocalcin and the z score of the lum bar spine (r=-0.381, p<0.05). Multiple linear regression analysis showed th at "free" osteocalcin was an independent risk factor for low bone mineral d ensity of the lumbar spine whereas serum vitamin D was not. Conclusions-The finding that a poor vitamin K status is associated with low bone mineral density in longstanding Crohn's disease may have implications for the prevention and treatment of osteoporosis in this disorder.