SUN-392 Bone Mineral Density and Body Mass Index in Men with Cystic Fibrosis

Abstract

Osteoporosis is an important endocrine complication of cystic fibrosis (CF). Low bone mass in CF patients has multiple contributing causes including vitamin D deficiency, calcium malabsorption, pulmonary infection and cytokine production, malnutrition, a sedentary life style, cumulative steroid dose, delayed puberty, and hypogonadism. The objective of this study was to examine the relationship between BMI and bone density of the hip and spine in adult men with CF. We conducted a retrospective chart review of adult men with CF receiving care at an academic medical center. Medical records of 43 men ages 19-60 (32.1±9.8) years were reviewed. 8 men with lung transplant, or receiving chronic glucocorticoid or androgen treatment were excluded. One subject was excluded as his BMI was >3SD above the mean. BMD was measured by dual-energy x-ray absorptiometry at the lumbar spine (LS) and hip. The mean ± SD BMI of the study population was 24.10 ± 5.24 kg/m2, mean LS BMD was 0.96 ± 0.204 g/cm2 and mean hip BMD was 0.701 ± 0.382 g/cm2. Men were divided into three groups: normal BMD, osteopenia, or osteoporosis, based on current guidelines. 8 (24%) men were found to have normal bone density (Z=0.40±0.60), 19 (56%) had osteopenia (Z= -1.57±0.67) and 7 (20%) had osteoporosis (Z= -3.27±0.83). Of these 7, 6 had osteoporosis of the LS only, and one patient had osteoporosis of the hip; 5 were being treated with a bisphosphonate. The three groups of men were similar in age (P=0.93). 25OH-vitamin D levels were 22.6±4.4, 35.6±12.7 and 27.0±13.4 ng/mL, respectively (p=0.03). There was a significant (p=0.023) difference in BMI among these three groups (26.33±4.80 vs 23.25 ± 3.01 vs 20.96±3.64 kg/m2). BMI was strongly positively correlated with LS BMD (r = 0.54, P<0.001) but not with BMD of the hip (r = 0.11, p=0.55). Moreover, LS BMD was highly predicted by body weight (r = 0.90, P<0.0001) but not significantly by height (r = 0.26, p=0.16). These findings indicate that CF-related bone disease (CF-RBD) affecting the LS is common in adult men, and that body weight is a major determinant of LS BMD in men with CF. Possible mechanisms for this association include signaling pathways related to nutritional status and sex steroids.