Fat absorption requires micellar solubilization. In a patient with ileal resection (>100 cm), which fat-soluble vitamin deficiency would be clinically most important to monitor and why?

• A Vitamin K, because it is exclusively absorbed in the ileum and is the most critical fat-soluble vitamin for coagulation
• B Vitamin D, because ileal absorption is critical for its enterohepatic circulation
• C Vitamin B12 (cobalamin), although not fat-soluble, becomes severely deficient due to loss of the only site of intrinsic factor-B12 complex absorption (terminal ileum). Fat-soluble vitamins (A, D, E, K) are absorbed throughout the small intestine ✓
• D Vitamin A, because retinol esters require ileal esterases for absorption

Explanation

The terminal ileum is the exclusive site of absorption for two specific molecules: (1) vitamin B12-intrinsic factor complex via cubilin receptors, and (2) bile acid reabsorption (enterohepatic circulation). Ileal resection >100 cm causes vitamin B12 deficiency (megaloblastic anemia) and bile acid malabsorption (steatorrhea, fat-soluble vitamin deficiency, and cholesterol gallstones). Fat-soluble vitamins A, D, E, K are absorbed throughout the proximal small intestine as long as micellar fat absorption is intact — but with ileal resection causing bile salt malabsorption, secondary steatorrhea will impair all fat-soluble vitamin absorption. However, B12 deficiency is direct and absolute (no alternative absorption pathway).

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.