One pathway, three passengers
Bile salts emulsify dietary fat, pancreatic lipase hydrolyzes triglycerides, and mixed micelles carry the fat-soluble vitamins to the enterocyte surface. Vitamins A, D, K, and E all depend on this route. Break any step and all of them are lost together.
Where the pathway commonly breaks
- Cholestatic liver disease, which reduces bile salt delivery to the intestine
- Pancreatic insufficiency, which reduces lipase activity
- Celiac disease and other mucosal disorders, which damage the absorptive surface
- Cystic fibrosis, which impairs both pancreatic enzyme secretion and bile flow
The combined deficiency signature
Vitamin A loss
- Night blindness
- Xerophthalmia and Bitot spots
- Squamous metaplasia of mucous epithelia
Vitamin D loss
- Rickets in children
- Osteomalacia in adults
- Low calcium and phosphate absorption
Vitamin K loss
- Prolonged prothrombin time
- Easy bruising and mucosal bleeding
- Nonfunctional factors II, VII, IX, X
Why this pattern points to fat
Water-soluble vitamins use different transporters and are not lost together in fat malabsorption. A patient who presents with visual, bone, and bleeding symptoms at the same time is therefore showing a fat-absorption problem, not three separate deficiencies.