Survival has steadily improved in cystic fibrosis (CF) over the last few decades, with the median survival age now older than 33 years, and over 40% of all individuals with CF older than 18 years (1). With this increase in survival, there has also been growing recognition of health issues unique to the adult population with CF (2). One of these issues is bone health, because studies using dual-energy x-ray absorptiometry measurements of bone density have determined that, despite their young age, approximately 20 to 25% of adults with CF have osteoporosis and another 40% have osteopenia (3-5). The etiology of this bone disease is multifactorial, with contributors including fat malabsorption (resulting in vitamin D malabsorption and abnormal calcium metabolism) (6-8), glucocorticoid therapy (9, 10), poor nutritional status (11), inadequate gonadal hormones (10, 12), and elevated circulating cytokines (13). Recognition of this increased risk of osteoporosis in CF has led to greater efforts to optimize vitamin D status and calcium absorption (4,14). The overall prevalence of vitamin D deficiency in adults with CF is strikingly high, with as many as 50 to 60% having 25-hydroxyvitamin D (25-OHD) levels below 20 ng/ml (5, 15). Data demonstrating that serum 25-OHD levels need to exceed 30 ng/ml to prevent a rise in serum parathyroid hormone (16) suggest that the prevalence of vitamin D deficiency in CF may be even higher.Because of the growing concern about bone disease in CF, the U.S. Cystic Fibrosis Foundation (CFF) convened a panel of experts to develop consensus treatment guidelines to optimize CF bone health, and these recommendations were recently published (17). The guidelines contained several specific recommendations regarding vitamin D. First, greater attention to maintaining adequate serum 25-OHD levels should occur, with levels being checked annually in the late fall with the goal of maintaining serum 25-OHD between 30 and 60 ng/ml (75-150 nmol/L). Second, all individuals with CF who are older than 1 year should receive 800 IU/day of oral ergocalciferol (vitamin D 2 ). Failure of this supplementation to maintain serum 25-OHD levels above 30 ng/ml should lead to aggressive repletion with high-dose oral ergocalciferol. The guidelines recommended a stepped approach for repletion, with an initial regimen of 50,000 IU/week of oral ergocalciferol for 8 weeks. Failure of this regimen to raise serum 25-OHD to over 30 ng/ml should lead to a second course of oral ergocalciferol with 50,000 IU/twice weekly for 8 weeks. Persistence of serum 25-OHD levels below 30 ng/ml despite these supplemental regimens should result in consideration of alternative modes of therapy, such as calcitriol or phototherapy. This treatment protocol was developed on the basis of data in individuals without CF, but was recognized as a "first step" in addressing the clear need for more aggressive vitamin D therapy in individuals with CF. Conference leaders stated a need for CF-specific data in the future on which to determine optimal dosing rec...

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