Fat-soluble vitamins in cystic fibrosis.

When cystic fibrosis (CF) was first recognized (Andersen, 1939), symptoms and signs of deficiency of vitamin A were common in infants with the condition. It was realized that pancreatic insufficiency from birth caused fat malabsorption and, therefore, malabsorption of the fat-soluble vitamins A, D, E and K. With the use of pancreatic enzyme replacement therapy and routine vitamin supplementation, clinical problems arising from deficiencies of the fat-soluble vitamins became uncommon in children with CF. However, CF patients are still at risk from vitamin deficiency if the diagnosis is made late (Brooks et al. 1990), if part of the small bowel has been resected (Bye et al. 1985) or if fat-soluble vitamin supplements are not taken (O’Donnell & Talbot, 1987). In addition, it has been recognized that factors other than simple malabsorption of fat may be important. For example, patients with CF have low circulating levels of retinol-binding protein, which is essential for the transport of retinol from the liver to the tissues (Rees Smith et al. 1972). Some patients may have low serum levels of retinol and retinolbinding protein despite raised liver concentrations of retinol, suggesting that its release from liver stores is impaired (Underwood & Denning, 1972). Reduced enterohepatic circulation of bile acids may also contribute to malabsorption of fat-soluble vitamins from the small bowel (Weber & Roy, 1985). In addition, patients with liver function abnormalities may have inadequate 25-hydroxylation of vitamin D (Friedman et al. 1985). The fat-soluble vitamin status of thirty-six infants consecutively identified by screening in Denver, Colorado was reported recently (Sokol et al. 1989). At a mean age of 51 (SE 26.7) d, 21% had low serum levels of retinol, 35% low 25-hydroxycholecalciferol levels and 38% low a-tocopherol levels and low total serum vitamin E:total lipids ratios. After treatment with pancreatic enzymes and vitamin supplements, all patients had normal serum levels of retinol and 25-hydroxycholecalciferol by 6 months of age but 10% remained vitamin E deficient. None of the infants had evidence of vitamin K deficiency. The vitamin status of thirty-six older patients in Leeds was investigated in 1981 in order to assess the adequacy of conventional vitamin supplementation and the effect of short-term supplementation with water-miscible forms of vitamin A and E (Congden et al. 1981). At that time patients were not receiving vitamin E supplements and serum vitamin E levels were low in 90% of patients and inversely correlated with the severity of the steatorrhoea, but responded well to treatment with 50 mg water-miscible vitamin E daily for 2 weeks. Despite receiving 1.2 mg oil-based vitamin A supplements daily, 40% of patients had low serum retinol levels and these correlated with the retinol-binding protein levels. Serum levels of retinol responded well to 2 weeks of treatment with 1.2 mg water-miscible vitamin A daily. Seven of twenty (35%) patients receiving vitamin D supplements (10 pg daily) had serum levels lower than 15 ng/ml and two (10%) had levels below the normal range. Unfortunately, water-miscible preparations of vitamin A and vitamin E are not readily available on prescription in the UK and tend to be rather unstable if stored for long periods. Therefore, most CF patients are still prescribed