Why are water-soluble vitamins (such as vitamin C, thiamine (B1), riboflavin (B2), pyridoxine (B6), and folate) necessary for patients undergoing dialysis, rather than fat-soluble vitamins?

Water-Soluble Vitamin Supplementation in Dialysis Patients

Patients undergoing dialysis require water-soluble vitamin supplementation rather than fat-soluble vitamins because of increased requirements during kidney failure, significant losses during dialysis treatments, and their critical role in preventing metabolic complications. 1

Why Water-Soluble Vitamins Are Necessary in Dialysis

Mechanism of Loss

• Water-soluble vitamins (B vitamins and vitamin C) are readily lost during dialysis treatments due to:
  • Direct removal in the dialysate effluent 1
  • Documented daily losses of approximately:
    • 68 mg of vitamin C
    • 0.3 mg of folate
    • 4 mg of thiamine (B1) 1
  • Increased utilization during critical illness and kidney failure 1

Specific Water-Soluble Vitamin Deficiencies

• In patients on chronic hemodialysis, the most commonly deficient micronutrients are:
  • Thiamine (B1): deficient in 24.7% of patients
  • Vitamin B6: deficient in 35.1% of patients
  • Zinc: deficient in 44.1% of patients 1

Clinical Consequences of Deficiency

• Elevated homocysteine levels, a cardiovascular risk factor in dialysis patients, are strongly correlated with deficiencies of:
  • Folate
  • Vitamin B6
  • Vitamin B12 1
• Vitamin deficiencies contribute to:
  • Impaired wound healing
  • Compromised immune function
  • Metabolic derangements 1

Fat-Soluble vs. Water-Soluble Vitamins

Why Fat-Soluble Vitamins Are Not Routinely Supplemented

• Fat-soluble vitamins (A, D, E, K) are:
  • Not significantly removed by dialysis 2
  • Can accumulate to toxic levels in patients with kidney failure 3
  • Studies show elevated plasma retinol levels in 100% of hemodialysis patients 3
  • Elevated plasma alpha-tocopherol (vitamin E) in 48% of patients 3

Monitoring and Supplementation Approach

• Water-soluble vitamin levels should be monitored regularly in dialysis patients 1
• Special attention should be given to:
  • Vitamin C
  • Folate
  • Thiamine 1
• Supplementation should be guided by serum levels and estimated dialysis losses 1

Practical Recommendations

• B vitamin supplementation is necessary to:

  • Replace losses from dialysis
  • Prevent elevation in serum homocysteine levels 1
  • Support metabolic functions 1

• Extended hours hemodialysis patients (>15 hours/week) are at particularly high risk of vitamin C deficiency and require careful monitoring 4

• Current guidelines recommend supplementation of water-soluble vitamins after each dialysis session, with particular attention to:

  • Thiamine (B1)
  • Riboflavin (B2)
  • Pyridoxine (B6)
  • Folate
  • Vitamin C 1

In conclusion, while fat-soluble vitamins can accumulate to toxic levels in dialysis patients, water-soluble vitamins are continuously lost during treatment and must be regularly supplemented to prevent deficiencies that can contribute to poor clinical outcomes.