Normal Vitamin D Level for Infants on Supplementation
For healthy infants receiving vitamin D supplementation, the target serum 25-hydroxyvitamin D [25(OH)D] level is >50 nmol/L (>20 ng/mL), which indicates sufficiency. 1
Target Serum Levels
The minimum threshold for vitamin D sufficiency in infants and children is a serum 25(OH)D concentration >50 nmol/L (>20 ng/mL). 1
This target applies to both term and preterm infants receiving appropriate supplementation. 1
Some authorities suggest higher targets of 30 ng/mL (75 nmol/L) for potential extra-skeletal benefits, though evidence for clinical benefit at these higher levels remains limited. 1
Standard Supplementation Doses
Term infants up to 12 months of age should receive 400 IU/day of vitamin D from all sources (breast milk, formula, or supplements). 1
The ESPGHAN Committee on Nutrition, American Academy of Pediatrics, and Institute of Medicine all recommend 400 IU/day as the standard dose for infants. 1
Preterm infants on parenteral nutrition should receive 200-1000 IU/day (or 80-400 IU/kg/day) depending on their clinical status. 1
Important Clinical Context
Vitamin D deficiency is extremely common in infants despite supplementation recommendations:
Research shows that 56% of newborns have severe vitamin D deficiency (<10 ng/mL), 31% have moderate deficiency (10-20 ng/mL), and only 4% have normal levels (>30 ng/mL) at birth. 2
Among infants with cystic fibrosis, 22% are deficient at newborn screening. 1
Even with standard 400 IU/day supplementation, 55% of term breastfed infants still have vitamin D insufficiency (<20 ng/mL) at 14 weeks of age. 3
Monitoring Recommendations
Routine biochemical testing of 25(OH)D levels is not recommended for healthy infants receiving standard supplementation. 4
For infants with malabsorption conditions (cystic fibrosis, liver disease, short bowel syndrome), monitor serum 25(OH)D annually and 3-6 months after any dosage change. 1
When monitoring is indicated, check levels preferably at the end of darker months when sun exposure is lowest. 1
Higher Dose Considerations
Recent evidence suggests 400 IU/day may be insufficient for many infants:
A 2022 randomized trial demonstrated that 800 IU/day reduces vitamin D insufficiency by 50% compared to 400 IU/day (24% vs 55% with insufficiency) with no toxicity. 3
The 800 IU/day dose prevented severe deficiency (<5 ng/mL) entirely, whereas 12% of infants receiving 400 IU/day developed severe deficiency. 3
No adverse events or vitamin D toxicity occurred with 800 IU/day supplementation. 3
Safety Thresholds
Vitamin D sufficiency is defined as 25(OH)D >50 nmol/L (>20 ng/mL). 1
Serum concentrations up to 240 nmol/L appear safe in children. 1
Toxicity (hypercalcemia and hyperphosphatemia) typically occurs only with serum concentrations >375 nmol/L. 1
Tolerable upper intake limits are 1000 IU/day for infants 0-6 months and 1500 IU/day for infants 7-12 months. 1