Vitamin D and Calcium Deposits in Tendons
The available evidence does not support a link between consuming large amounts of vitamin D and calcium deposits in tendons. The primary documented adverse effect of high-dose vitamin D and calcium supplementation is kidney stones (nephrolithiasis), not tendon calcification.
Key Evidence on Adverse Effects
The most robust evidence comes from the Women's Health Initiative (WHI) trial, which demonstrated that supplementation with 400 IU vitamin D3 and 1000 mg calcium daily increased the risk of kidney stones (hazard ratio 1.17), with an absolute risk increase from 2.1% to 2.5% 1. This represents the primary calcification concern with vitamin D and calcium supplementation in clinical practice.
What Actually Happens with Vitamin D Supplementation
- Vitamin D controls calcium absorption in the small intestines and maintains calcium homeostasis between blood and bones 1
- The mechanism of harm from excessive vitamin D relates to hypercalcemia, hypercalciuria, and mineral deposits in soft tissues generally—not specifically tendons 2
- Vascular calcification has been studied in the cardiovascular context, where vitamin D actually appears to control matrix metalloproteinases involved in vascular calcification rather than promote it 1
Specific Tissue Calcification Risks
The documented calcification risks from vitamin D excess include:
- Nephrocalcinosis (kidney calcification): Reported in 30-70% of patients with X-linked hypophosphatemia receiving high-dose phosphate and active vitamin D therapy 1
- Soft tissue calcification: A recognized consequence of vitamin D toxicity, but this occurs at doses far exceeding typical supplementation 3
- No evidence for tendon-specific calcification in any of the major trials or guidelines reviewed
Safety Thresholds
- Daily doses of 800-1000 IU vitamin D are considered safe for prevention and correction of deficiency 2
- The accepted upper safety limit is 4000 IU/day, though this has been challenged based on emerging evidence 2
- Vitamin D toxicity causing soft tissue calcification requires excessive amounts beyond standard supplementation ranges 3
Clinical Implications
If you are concerned about calcification with vitamin D supplementation, monitor for kidney stones rather than tendon deposits. The evidence consistently points to renal calcification as the primary risk, particularly when combining vitamin D with calcium supplementation 1. There is no established mechanism or clinical evidence linking standard or even high-dose vitamin D supplementation to tendon calcification specifically.