BONE MASS AND VITAMIN-D DEFICIENCY IN ADULTS WITH ADVANCED CYSTIC-FIBROSIS LUNG-DISEASE

Osteoporosis and fractures are increasingly recognized in children and adults with cystic fibrosis. To investigate the prevalence and pathog enesis of osteoporosis and low bone mass in adults with advanced pulmo nary disease due to cystic fibrosis, we examined the relationships bet ween bone mineral density (BMD), anthropomorphic variables, pulmonary status, glucocorticoid therapy, and vitamin D concentrations. BMD of t he lumbar spine, hip, and proximal radius was measured by dual energy X-ray absorptiometry in 30 white adults (16 women), age 30 +/- 2 yr (m ean +/- SEM). Compared with a normal control population, the patients had significantly reduced BMD at the lumbar spine (17 +/- 3%), total h ip and femoral neck (24 +/- 3% and 20 +/- 4%, respectively). The radiu s was significantly less demineralized (4 +/- 2%; p less than or equal to 0.003) than the other sites. Moreover, only 21% of patients with c ystic fibrosis had normal BMD (T score > -1.0) at the lumbar spine, 23 % at the hip sites, and 39% at the radius. Age, weight, and body mass index (BMI) were most strongly correlated with bone mass, whereas gluc ocorticoid therapy and pulmonary function were not predictive. Despite oral vitamin D (400 to 800 IU daily), the mean serum 25-hydroxyvitami n D (25-OHD) concentration was at the low end of the normal range (16 +/- 2 ng/ml; normal 10 to 52 ng/ml); 8 of 20 patients (40%) had frankl y low (less than or equal to 10 ng/ml) levels. BMD was significantly l ower in patients with low 25-OHD concentrations at the lumbar spine (0 .774 +/- 0.02 versus 0.913 +/- 0.04 g/cm(2); p = 0.01) and total hip ( 0.648 +/- 0.04 versus 0.811 +/- 0.04 g/cm(2); p = 0.01). Vertebral fra ctures were present in 19% of subjects and 41% had a confirmed history of previous fracture. In summary, osteoporosis, low bone mass, and fr actures are common in adults with advanced cystic fibrosis lung diseas e. Despite oral supplements, vitamin D deficiency is also common and i s associated with more severe demineralization at the lumbar spine and hip. We conclude that the widespread practice of oral supplementation with 400 to 800 units of vitamin D is ineffective in maintaining norm al vitamin D stores in many patients with cystic fibrosis. To ensure a dequacy of vitamin D stores, measurement of serum 25-OHD should be inc luded in the routine management of patients with cystic fibrosis.