Low serum and bone vitamin K status in patients with longstanding Crohn's disease: another pathogenetic factor of osteoporosis in Crohn's disease?
- aDepartment of Gastroenterology and Hepatology, University Hospital Maastricht, Maastricht, the Netherlands, bDepartment of Biochemistry, Maastricht University, Maastricht, the Netherlands
- Dr E J Schoon, PO Box 5800, NL-6202 AZ Maastricht, the Netherlands.
- Accepted 31 October 2000
BACKGROUND A high prevalence of osteoporosis is reported in Crohn's disease. The pathogenesis is not completely understood but is probably multifactorial. Longstanding Crohn's disease is associated with a deficiency of fat soluble vitamins, among them vitamin K. Vitamin K is a cofactor in the carboxylation 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 receiving less than 5 mg of prednisolone daily. Serum levels of vitamins D and K, triglycerides, and total immunoreactive osteocalcin, as well as uncarboxylated osteocalcin (“free” osteocalcin) were determined. The hydroxyapatite 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 hydroxyapatite 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 was 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 lumbar spine (r=−0.381, p<0.05). Multiple linear regression analysis showed that “free” osteocalcin was an independent risk factor for low bone mineral density 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.
- Abbreviations used in this paper:
- bone mineral density
- body mass index
- Crohn's disease
- Crohn's disease activity index
- gamma carboxyglutamate
- glutamic acid
- hydroxyapatite binding capacity
- bound osteocalcin (carboxylated)
- free osteocalcin (uncarboxylated)
- total osteocalcin