Relationships between vitamin D, parathyroid hormone and bone mineral density in inflammatory bowel disease

Objectives. To explore the relationships between vitamin D intake, serum parathyroid hormone (PTH) and 25-hydroxyvitamin D (250HD) concentrations, and bone mineral density (BMD) in inflammatory bowel disease (IBD).
Setting. A university hospital clinic in Finland.
Subjects. One hundred and fifty randomly selected patients with IBD from the hospital register and 73 healthy controls.
Measurements. BMD of the lumbar spine and the proximal femur was measured with dual energy X-ray absorptiometry. Vitamin D intake and serum levels of 250HD and PTH were determined.
Results. The IBD patients had a lower serum 250HD concentration (28.4 SD 12.0] nmol L^-1) than the controls (36.1 16.7] nmol L^-1; P =0.001), whereas no differences in the vitamin D intake or the serum PTH levels were found. The serum 250HD concentrations and the vitamin D intake of the patients with ulcerative colitis ( n =67) were similar to those of the Crohn's disease patients ( n =76). The patients with Crohn's disease of the small bowel had slightly, but not significantly, lower serum 250HD concentrations (25.6 11.0] nmol L^-1) than the other Crohn's disease patients (31.4 14.3] nmol L^-1; P =0.061). In the IBD patients, the vitamin D intake and the serum 250HD and PTH concentrations were not associated with BMD.
Conclusions. Patients with IBD have lower serum levels of 250HD than healthy controls, but similar serum PTH concentrations and vitamin D intake. Vitamin D intake, and the serum levels of 250HD and PTH are not associated with BMD, and malabsorption is unlikely to be a major factor in the aetiology of bone loss in unselected IBD patients.