Learning Objective: Describe the absorption, physiological roles, and clinical implications of deficiencies or toxicities of the fat-soluble vitamins (A, D, E, and K).
Overview
Fat-soluble vitamins (A, D, E, and K) are absorbed along with dietary fats in the small intestine, requiring bile salts, pancreatic enzymes, and an intact ileum for proper absorption. Unlike water-soluble vitamins, they accumulate in body fat, making toxicity more likely when consumed in excess.
| Vitamin | Key Function | Deficiency Manifestations |
|---|---|---|
| A (Retinol) | Vision, epithelial differentiation | Night blindness, dry skin |
| D (Calcitriol) | Calcium and phosphate regulation | Rickets, osteomalacia, hypocalcemia |
| E (Tocopherol) | Antioxidant: protects RBC membranes | Hemolytic anemia, ataxia |
| K (Phylloquinone) | γ-carboxylation of clotting factors II, VII, IX, X | Bleeding tendency, prolonged PT |
Activity:
Clinical relevance:
Malabsorption syndromes (e.g., celiac disease, cystic fibrosis, chronic pancreatitis) or chronic mineral oil use can impair absorption and cause fat-soluble vitamin deficiencies.
