What nutrient's absorption is mostly affected by the duodenal switch, or biliopancreatic diversion by Scopinaro's (Biliopancreatic Diversion) procedure?

Vitamin D Absorption is Most Severely Affected

Vitamin D (Option B) is the nutrient most profoundly affected by biliopancreatic diversion (BPD) and duodenal switch procedures, with deficiency rates reaching 63-69% by the fourth postoperative year despite supplementation. 1, 2

Why Vitamin D is Most Affected

Malabsorptive Mechanism

• BPD/Scopinaro's procedure creates only a 50-cm "common tract" where digestion and absorption occur, drastically limiting the intestinal surface area available for fat-soluble vitamin absorption 1
• The procedure bypasses the duodenum and proximal jejunum—the primary sites for vitamin D absorption 1
• Fat malabsorption inherent to these procedures directly impairs absorption of all fat-soluble vitamins (A, D, E, K), but vitamin D shows the most persistent and severe deficiency pattern 2

Clinical Evidence of Severity

• Progressive worsening over time: Vitamin D deficiency affects 63% of patients by year 4, with 70% showing deficiency at 2 years post-BPD/DS 2, 3
• Secondary metabolic consequences: 62-69% of patients develop secondary hyperparathyroidism due to vitamin D deficiency, leading to abnormal calcium metabolism and increased bone resorption 2, 3, 4
• Refractory to standard supplementation: Even with initial prescriptions of 1900 IU daily, patients require escalation to at least 7000 IU daily, with some needing 50,000 IU weekly to daily 3, 1

Comparison with Other Nutrients

Vitamin A (Option A)

• While vitamin A deficiency is also common (69% by year 4), it responds more predictably to supplementation with 50,000 IU daily 2, 3

B Vitamins Including B12 (Options A & C)

• B12 deficiency occurs but is less severe than fat-soluble vitamin deficiencies after malabsorptive procedures 1
• B vitamins are water-soluble and absorbed throughout the small intestine, making them less vulnerable to the shortened common channel 1

Iron (Option D)

• Iron deficiency is significant (affecting 40-46% of patients), but occurs through different mechanisms related to reduced gastric acid and bypassed duodenum 5
• Iron deficiency is more manageable with supplementation (200 mg daily) compared to the persistent vitamin D issues 3

Clinical Implications

Required Supplementation Protocol

• Initial prescription must include at least 7000 IU vitamin D daily with 3000 mg calcium 3
• Severe malabsorption cases require 50,000 IU vitamin D 1-3 times weekly to daily 1
• Oral calcitriol (active vitamin D) may be necessary in refractory cases 1

Monitoring Requirements

• Target 25(OH)D levels ≥30 ng/ml (75 nmol/l) 1
• Monitor PTH levels for secondary hyperparathyroidism 2, 3
• Lifelong monitoring is mandatory, as deficiencies persist and worsen over time 1, 5

Common Pitfalls

• Underestimating initial supplementation needs: Standard multivitamin doses are grossly inadequate for BPD patients 3
• Failing to recognize the cascade effect: Vitamin D deficiency leads to calcium malabsorption, secondary hyperparathyroidism, and ultimately bone disease 2, 4
• Inadequate long-term follow-up: Deficiencies worsen progressively, with only 35% maintaining normal vitamin D levels at 10 years despite supplementation 4