Bone health, daily physical activity, and exercise tolerance in patients with cystic fibrosis.

Background: Daily physical activity (PA) may be an excellent tool for the maintenance of bone health in patients with cystic fibrosis (CF). The aim of this study was to analyze the possible association between physical capacity and activity and bone mineral density (BMD) in young adults with CF. A secondary goal was to evaluate vertebral fractures in this population.

Methods: A cross-sectional study was conducted in 50 patients with CF who were clinically stable and aged > 16 years but not lung transplant recipients. PA was quantified with a portable motion monitor (BodyMedia Fit Armband). Cardiopulmonary exercise and 6-min walk tests were used to assess exercise capacity. BMD was obtained from dual-energy x-ray absorptiometry of the lumbar column, hip, and whole body. To analyze vertebral fractures and deformity, we performed the Genant and Cobb methods.

Results: Daily PA time at low (3-4.8 metabolic equivalent tasks [METs]) and moderate (4.8-7.2 METs) intensity, respectively, was correlated with Z score (BMD) of the lumbar column (r = 0.36, P < .01 and r = 0.59, P < .001), the neck of femur (r = 0.51, P < .001 and r = 0.72, P < .001), and the total hip (r = 0.54, P < .001 and r = 0.74, P < .001). PA, BMI, age, and sex were predictors of BMD. Vertebral fractures correlated with kyphosis (r = 0.42, P = .02), but not with BMD. Patients who were mildly and severely affected differed in vertebral fracture rate and kyphosis prevalence (P = .002 and P = .013, respectively).

Conclusions: The most active patients with better exercise capacity had higher BMD. Those with more affected pulmonary function had a greater prevalence of vertebral fractures and dorsal kyphosis.