Vitamin A Status in Cystic Fibrosis in the Current Era of CFTR-Directed Therapies

Vitamin A plays an important role in multiple homeostatic functions such as vision, immunity, epithelial cell integrity and differentiation, cell signaling, pulmonary function, reproduction, growth, and development. Vitamin A deficiency was described in people with cystic fibrosis (pwCF) due to a multitude of causes, such as suboptimally managed exocrine pancreatic insufficiency, advanced cystic fibrosis-related liver disease (aCFLD), and a history of intestinal resection, and is generally rare in contemporary practice. Apart from true vitamin A deficiency, low vitamin A levels may also be noted in various inflammatory states, as vitamin A is a negative acute-phase reactant. In the current era of cystic fibrosis (CF) transmembrane-conductance regulator (CFTR)-directed therapies, there is a paradigm shift in vitamin A status, with deficiency statuses becoming rarer, and instead higher serum vitamin levels (in some cases, even in the hypervitaminosis range) are increasingly reported. People with aCFLD, renal insufficiency, post-lung transplantation, and pregnancy are prone to vitamin A toxicity. Hence, CF clinicians should be proactive in evaluating these abnormalities and proficient in managing both deficiency and toxicity, as both these conditions can be associated with adverse outcomes. In this review, we detailed the basics of vitamin A metabolism, manifestations of both vitamin A deficiency and excess, and their clinical implications in pwCF.