Vitamin D Supplementation Increases the Risk of Kidney Stones
Vitamin D supplementation does not help prevent kidney stones and may actually increase the risk of stone formation, particularly when combined with calcium supplements. 1
Evidence on Vitamin D and Kidney Stone Risk
Increased Risk with Supplementation
The U.S. Preventive Services Task Force (USPSTF) found adequate evidence that supplementation with vitamin D and calcium increases the incidence of renal stones 1. In the Women's Health Initiative (WHI) study, women taking supplemental vitamin D and calcium experienced a statistically significant increased incidence of renal stones, with one woman diagnosed with a urinary tract stone for every 273 women who received supplementation over a 7-year follow-up period 1.
Research shows that vitamin D supplementation can lead to:
- Increased risk of hypercalciuria (elevated calcium in urine) 2, 3
- Increased risk of hypercalcemia (elevated calcium in blood) 2
A meta-analysis of 48 studies with 19,833 participants found that long-term vitamin D supplementation resulted in:
- 64% increased risk of hypercalciuria (RR: 1.64; 95% CI: 1.06,2.53) 2
- 54% increased risk of hypercalcemia (RR: 1.54; 95% CI: 1.09,2.18) 2
Mechanism of Action
Vitamin D, especially its active metabolite calcitriol, increases intestinal calcium absorption. Since urinary calcium excretion is directly correlated with digestive calcium absorption, vitamin D metabolites can increase calciuria and potentially promote urinary stone formation 4. This is particularly concerning for individuals who are predisposed to hypercalciuria.
High-Dose Vitamin D Risks
A randomized controlled trial comparing high-dose vitamin D (10,000 IU/day) with standard dose (600 IU/day), both with calcium supplementation, found that the odds of developing hypercalciuria were 3.6 times higher in the high-dose group 3. This suggests that higher doses of vitamin D, particularly when combined with calcium supplements, may significantly increase the risk of kidney stones in susceptible individuals.
Special Considerations
Vitamin D Deficiency in Stone Formers
Interestingly, vitamin D deficiency is actually prevalent among stone formers 5. However, this doesn't mean supplementation is beneficial for preventing stones. Short-term vitamin D repletion in stone formers with vitamin D deficiency may not increase urinary calcium excretion significantly 5, but long-term supplementation, especially at higher doses, could increase risk.
Calcium Intake Considerations
It's important to note that while calcium supplements may increase stone risk when taken with vitamin D, dietary calcium actually has a protective effect against kidney stones by:
- Reducing intestinal oxalate availability
- Reducing urinary oxalate excretion 6
However, calcium supplementation given between meals might increase urinary calcium excretion without the beneficial effect on oxalate 6.
Clinical Recommendations
For patients concerned about kidney stone prevention:
- Avoid vitamin D supplements if you have a history of kidney stones or are at high risk
- Maintain adequate dietary calcium rather than taking supplements
- Focus on other proven stone prevention strategies:
Cautions and Pitfalls
- Don't assume vitamin D supplements are harmless - they can increase stone risk in susceptible individuals
- Don't restrict dietary calcium as this may actually increase stone risk
- Be cautious with vitamin C supplements as doses ≥1000 mg/day may increase stone risk by 40% due to increased oxalate excretion 1
- Remember that kidney stone disease is multifactorial, influenced by both genetic predisposition and environmental factors 6
In conclusion, vitamin D supplementation should be approached with caution in individuals with a history of kidney stones or risk factors for stone formation, as it may increase the risk of hypercalciuria and stone development rather than helping prevent them.