Low bone mineral density in adults with cystic fibrosis

Background-Patients with cystic fibrosis have several risk factors for the development of low bone mineral density (BMD). To identify the prevalence a nd clinical correlates of low BMD in adult patients with cystic fibrosis, d ensitometry was performed in 151 patients (83 men) aged 15-52 years. Methods-BMD was measured in the lumbar spine (L1-4) using dual energy x ray absorptiometry (DXA) and quantitative computed tomography (QCT). It was al so measured in the proximal femur (total hip and femoral neck) using DXA, a nd in the distal and ultra distal forearm using single energy x ray absorpt iometry (SXA). Biochemical markers of bone turnover, vitamin D levels, para thyroid hormone levels, and a variety of anthropometric variables were also assessed. Results-The mean (SD) BMD Z score was -0.73 (0.85) in the distal forearm, - 0.31 (0.92) in the ultra distal forearm, -1.21 (1.18) in the lumbar spine u sing DXA, -0.56 (1.36) in the lumbar spine using QCT, -1.25 (1.30) in the f emoral neck, and -1.01 (1.14) in the total hip. 34% of patients had a BMD Z score of -2 or less at one or more skeletal sites. Body mass index (0.527, p = 0.01), percentage predicted forced expiratory volume in one second (0. 388, p = 0.01), and physical activity (0.249, p = 0.05) were positively rel ated to the mean BMD Z score. Levels of C reactive protein (-0.328, p = 0.0 1), parathyroid hormone (-0.311, p = 0.01) and biochemical markers of bone turnover (osteocalcin -0.261 and bone specific alkaline phosphatase -0.249, p = 0.05) were negatively related to the mean BMD Z score. Vitamin D insuf ficiency (25-hydroxyvitamin D <15 ng/ml) was prevalent (53/139 patients, 38 %) despite supplementation with 900 IU vitamin D per day. Conclusions-Low bone density is prevalent in adult patients with cystic fib rosis. Current levels of vitamin D supplementation appear to be inadequate.