Osteoporosis diminishes the quality of life in adults with cystic fibrosis (CF). Vitamin D deficiency resulting from malabsorption may be a factor in the etiology of low bone mineral density (BMD) in patients with CF. Objective: Absorption of oral ergocalciferol (vitamin D 2 ) and the consequent response of 25-hydroxyvitamin D in 10 adults with CF and exocrine pancreatic insufficiency was compared with that of 10 healthy control subjects. Design: In this pharmacokinetic study, CF patients and

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... ntrol subjects were pair-matched on age, sex, and race. Each subject consumed 2500 g oral vitamin D 2 with a meal. The CF group also took pancreatic enzymes that provided ≥ 80 000 U lipase. Blood samples were obtained at baseline and at 5, 10, 24, 30, and 36 h after vitamin D 2 consumption to measure serum vitamin D 2 and 25-hydroxyvitamin D concentrations. Results: Vitamin D 2 concentrations in all subjects were near zero at baseline. CF patients absorbed less than one-half the amount of oral vitamin D 2 that was absorbed by control subjects (P < 0.001). Absorption by the CF patients varied greatly; 2 patients absorbed virtually no vitamin D 2 . The rise in 25-hydroxyvitamin D in response to vitamin D 2 absorption was significantly lower over time in the CF group than in the control group (P = 0.0012). Conclusions: Vitamin D 2 absorption was significantly lower in CF patients than in control subjects. These results may help explain the etiology of vitamin D deficiency in CF patients, which may contribute to their low BMD. Am J Clin Nutr 2001;73:602-6.