Vitamin D and Chronic Kidney Disease
The kidney is the only organ in the body that can activate 25(OH)D into calcitriol (1,25(OH)₂D) — the hormonally active form. As kidney function declines, so does that conversion, and the entire mineral metabolism cascade breaks down. Vitamin D management in CKD is different from the general population and requires nephrology input.
The CKD-MBD cascade
"CKD-Mineral and Bone Disorder" describes the linked derangements of calcium, phosphorus, parathyroid hormone (PTH), and vitamin D that develop from CKD stage 3 onward. As eGFR falls: 1α-hydroxylase activity drops → calcitriol falls → intestinal calcium absorption falls → PTH rises → phosphorus accumulates → vascular calcification and renal osteodystrophy develop.
Cholecalciferol vs calcitriol vs analogues
- Cholecalciferol / ergocalciferol — the "nutritional" vitamin D you buy OTC. Useful in early CKD to correct 25(OH)D deficiency, but as the kidney fails there's less activation.
- Calcitriol (1,25(OH)₂D) — the active hormone; used in dialysis patients to suppress PTH. Risks hypercalcaemia; requires monitoring.
- Paricalcitol, doxercalciferol — synthetic vitamin D analogues designed to suppress PTH with less hypercalcaemia. Standard in advanced CKD and dialysis.
- Calcifediol (25(OH)D) — bypasses hepatic 25-hydroxylation; useful when malabsorption or hepatic disease coexists.
KDIGO guidance
Kidney Disease: Improving Global Outcomes (KDIGO 2017 update): correct 25(OH)D deficiency in CKD stages 3–5 with standard cholecalciferol. Do not routinely give calcitriol or vitamin D analogues in CKD 3–4; reserve for CKD 4–5 with progressively rising PTH. In dialysis, active vitamin D and calcimimetics (cinacalcet, etelcalcetide) target PTH suppression with defined ranges.
What you should NOT do
- Don't self-prescribe high-dose vitamin D if you have advanced CKD — hypercalcaemia in CKD accelerates vascular calcification.
- Don't use "potassium-sparing" salt substitutes or start high-potassium supplements without discussing with your nephrologist.
- Don't take calcium supplements above what's prescribed — CKD patients often accumulate calcium.
- Do report new symptoms — bone pain, itching, muscle weakness — to your kidney team.