Vitamin D deficiency is common in chronic kidney disease (CKD)—especially among people receiving hemodialysis. But similar to the controversy around optimal levels in the general population, there remains questions in this population too.
Why Vitamin D Matters in CKD
As kidney function declines, so does the body’s ability to activate vitamin D.
This has downstream effects:
- Reduced calcium absorption from the gut
- Increased parathyroid hormone (PTH) levels
- Increased bone resorption
We worry about this because people living with kidney disease are at an increased risk of hip fracture. And importantly—as kidney function goes down, the CKD population experiences fractures at younger ages and at higher rates than the general population.
What Vitamin D Level Is “Enough”?
This is where things get messy.
One cited study (Priemel et al., 2010) found that 25(OH)D levels >75 nmol/L were associated with no pathological bone mineralization defects.
That sounds convincing—until you look closer.
When the Institute of Medicine (IOM) reviewed the same data, they noted:
- Very few patients had bone defects below 50 nmol/L
- Even at 25 nmol/L, more than half of patients had no bone abnormalities
Same data. Very different interpretations.
What About PTH Suppression?
Another common argument for higher vitamin D targets is PTH reduction.
But again, the evidence is inconsistent.
In the DRI report, the authors created a table summarizing studies that reported which levels of Vitamin D were associated with a PTH plateau.
| 25(OH)D Level | Reference |
| <30nmol/L | Ooms et al. (1995a) |
| <50nmol/L | Malabanan et al. (1998)Levis et al. (2005)Steingrimsdottir et al. (2005)Aloia et al. (2006a) |
| <75nmol/L | Vieth et al. (2003)Holick et al. (2005)Durazo-Arvizu et al. (2010) |
| ~88nmol/L | Kinyamu et al. (1998) |
| 100-125nmol/L | Krall et al. (1989)Dawson-Hughes et al. (1997a) |
| No plateau | Bates et al. (2003)Benjamin et al. (2009) |
| No relationship | Rucker et al. (2002) |
Bottom line: There is no universally agreed-upon vitamin D level that “optimizes” PTH.
A Real-World Study in Hemodialysis Patients
A recent Canadian study (Holden et al., 2024) helps bring this into a more practical context.
What they did:
- Measured 25(OH)D every 12 weeks
- Treated levels <75 nmol/L with:
- 50,000 IU weekly until replete
- Then 50,000 IU monthly for maintenance
What they found:
- 15% of patients were deficient at baseline (<25 nmol/L)
- Deficiency was more common in winter
- Lower vitamin D levels were associated with:
- Higher phosphorus
- Lower calcium
After supplementation:
- PTH decreased by ~7%
- Phosphorus decreased by ~3%
- Alkaline phosphatase decreased by ~5%
But importantly:
There were no additional improvements once levels exceeded 75 nmol/L.
So… Does This Actually Matter?
Yes—vitamin D supplementation improves lab values.
But:
- The changes are modest
- We don’t know if they translate to:
- Fewer fractures
- Better cardiovascular outcomes
- Improved survival
Final Thoughts
Treating vitamin D deficiencies with 50,000IU vitamin D either weekly or monthly to achieve 25(OH)D targets of 75nmol/L was associated with modest reductions in PTH, PO4 and Alk Phos levels.
- In order to achieve 75nmol/L likely as many as 80% of Canadian HD patients will require a Vitamin D supplement.
It is unknown if this type of supplementation improves hard outcomes such as risk of fractures or cardiovascular disease. Though the relative risk of therapy was demonstrated to be low.
