Vitamin D Toxicity Threshold in Infants
Vitamin D supplementation should be stopped when serum 25-hydroxyvitamin D (25-OH-D) levels exceed 150 ng/mL (375 nmol/L), as this threshold is associated with acute hypercalcemia and hyperphosphatemia. 1, 2
Understanding Toxicity Levels
The definition of vitamin D toxicity is based on serum levels rather than dosing alone:
- Toxicity threshold: Serum 25(OH)D >150 ng/mL (375 nmol/L) indicates vitamin D toxicity and requires immediate discontinuation 1, 2
- Hypervitaminosis D: Serum 25(OH)D >100 ng/mL (250 nmol/L) is considered excessive and warrants stopping supplementation 3
- Target therapeutic range: 20-30 ng/mL (50-75 nmol/L) for sufficiency 4, 1
Safe Upper Intake Limits by Age
The Institute of Medicine established age-specific daily upper tolerable limits to prevent toxicity in healthy infants:
Important caveat: These upper limits apply to chronic daily intake. Prolonged intake up to 10,000 IU/day appears safe in older populations, but infants are particularly vulnerable to toxicity even at lower doses. 1, 6
Clinical Manifestations of Toxicity
When serum levels exceed safe thresholds, infants may present with:
- Hypercalcemia (the hallmark finding) 7, 3, 2
- Hypercalciuria and nephrocalcinosis 7, 6
- Confusion, apathy, recurrent vomiting, abdominal pain 2
- Polyuria, polydipsia, and dehydration 2
Monitoring Strategy
For infants on vitamin D supplementation at or above upper tolerable limits, obtain serum 25(OH)D levels every 3-6 months. 4, 6
- Check levels 3-6 months after any dosage change 4
- The Pediatric Endocrine Society recommends monitoring when long-term supplementation is at or above upper intake levels 6
- Annual monitoring is sufficient for standard maintenance doses (400 IU/day) 4, 5
Critical Pitfalls to Avoid
Manufacturing errors and dosing mistakes are the most common causes of infant vitamin D toxicity:
- One case report documented an infant receiving ~50,000 IU/day for 2 months due to a supplement containing 6,000 IU/drop instead of the labeled 2,000 IU/drop, resulting in severe hypercalcemia and nephrocalcinosis 7
- Over-the-counter supplements lack stringent FDA quality control and may contain significantly different amounts than labeled 7
- Prescription errors or parental misunderstanding of dosing instructions can lead to massive overdoses (240,000-4,500,000 IU total intake reported in toxicity cases) 6
Rare cases of toxicity have occurred even with recommended doses (400 IU/day) in infants with underlying vitamin D hypersensitivity or metabolic disorders. 6, 8 This underscores the importance of monitoring serum levels when symptoms develop, even with appropriate dosing.
When to Stop Supplementation Immediately
Discontinue vitamin D and seek urgent medical evaluation if: