14.3 Vitamin & Mineral Supplementation

Routine Supplementation in Healthy Children

Vitamin D

Human milk is low in vitamin D (about 15-50 IU/L), so the American Academy of Pediatrics (AAP) recommends 400 IU/day for all breastfed and partially breastfed infants, beginning in the first days of life. Formula-fed infants meet needs only once intake reaches roughly 1 L (32 oz)/day of formula (formulas contain ~400 IU/L); below that volume they also need 400 IU/d. The DRI Recommended Dietary Allowance rises to 600 IU/d from age 1 through 18 years — a common exam trap is applying 400 IU to a school-age child. Tolerable Upper Intake Levels (ULs) for vitamin D are 1,000 IU (0–6 mo), 1,500 IU (6–12 mo), 2,500 IU (1–3 y), 3,000 IU (4–8 y), and 4,000 IU (9–18 y). Serum 25-hydroxyvitamin D ≥20 ng/mL defines sufficiency by the Institute of Medicine; the Endocrine Society prefers ≥30 ng/mL — know both thresholds.

Iron

Iron deficiency is the most common pediatric nutrient deficiency and impairs neurodevelopment even without anemia. Supplementation rules:

• Preterm infants: breast milk plus low fetal iron stores make preterms the highest-risk group. AAP guidance: elemental iron 2 mg/kg/d starting at 4–6 weeks of age and continuing through 12 months for breastfed preterm infants; those on iron-fortified formula may meet part of this from formula, but supplementation is typically still required to reach 2 mg/kg/d.
• Exclusively breastfed term infants: 1 mg/kg/d starting at 4 months and continuing until iron-rich complementary foods (meats, iron-fortified cereal) supply adequate intake.
• Screening: universal hemoglobin screening at 12 months; hemoglobin <11.0 g/dL (6 months–5 years) indicates anemia by WHO/CDC cutoffs. DRI reference points: 7–12 months need 11 mg/d (RDA, reflecting low bioavailability of complementary-food iron); 1–3 years need 7 mg/d. The UL for iron is 40 mg/d in children, and iron overdose remains a leading cause of pediatric poisoning death — childproof storage is part of counseling.

Fluoride

Fluoride reduces caries risk; supplementation depends on local water fluoride concentration (optimal 0.7 mg/L) and begins at 6 months of age — never before, because of fluorosis risk during enamel formation. Standard schedule when water fluoride is <0.3 ppm: 6 months–3 years, 0.25 mg/d; 3–6 years, 0.5 mg/d; 6–16 years, 1.0 mg/d. At water fluoride 0.3–0.6 ppm, doses halve (none under 3 y); above 0.6 ppm, no supplement. Breastfed infants receive negligible fluoride from milk; exclusive formula made with fluoridated water contributes intake and modest fluorosis risk. Dental fluorosis (enamel mottling) from chronic excess is the signature adverse effect.

Condition-Specific Supplementation

Fat-Soluble Vitamins (ADEK) in Cystic Fibrosis and Cholestasis

Cystic fibrosis (CF): pancreatic insufficiency causes fat malabsorption and, with it, malabsorption of vitamins A, D, E, and K. CF Foundation guidance is to begin ADEK supplementation (CF-specific multivitamins with higher, often water-miscible, ADEK content) at diagnosis, alongside pancreatic enzyme replacement, and to monitor levels at least annually — serum retinol, 25-hydroxyvitamin D, alpha-tocopherol (ideally tocopherol:cholesterol ratio), and INR/PT for vitamin K status. Vitamin K deficiency is underdiagnosed because routine coagulation tests may stay normal until deficiency is advanced. Night blindness (A), rickets/osteopenia (D), hemolytic anemia and neuropathy (E), and coagulopathy (K) are the deficiency signatures.

Cholestatic liver disease (biliary atresia, Alagille, PFIC): impaired bile flow causes the same four-vitamin malabsorption, often more severely. Infants with cholestasis need aggressive, frequently water-miscible (e.g., TPGS-based vitamin E) ADEK dosing with serial monitoring; vitamin K correction of a prolonged INR is both treatment and a clue that deficiency — not synthetic liver failure — is the cause.

Restricted Diets

• Inborn errors of metabolism: the medical food (e.g., phenylalanine-free formula in PKU) supplies most micronutrients; inadequate medical-food intake or reliance on 'low-protein' table foods alone risks vitamin B12, iron, calcium, zinc, selenium, and essential fatty acid deficiency. Documented B12 and iron deficiency occur in poorly managed low-phe diets.
• Ketogenic diet therapy: carbohydrate-free, nutritionally incomplete by design. Standard of care includes a sugar-free multivitamin with minerals plus calcium and vitamin D; selenium, zinc, copper, and magnesium are monitored because deficiency (including cardiomyopathy from selenium deficiency) and nephrolithiasis are recognized complications.
• Vegan/vegetarian: vitamin B12 supplementation is non-negotiable, including for exclusively breastfed infants of vegan mothers (maternal milk B12 reflects maternal status). Also plan vitamin D, calcium, zinc, iron, iodine, riboflavin, and DHA; large volumes of soy or nut 'milks' that are unfortified and low in protein/energy are a frequent cause of toddler faltering growth.

Supplement Safety and Upper Limits

'Natural' does not mean safe. Key principles for the exam: the UL is the highest daily intake unlikely to cause harm, not a target; exceeding vitamin A ULs (600 µg RAE at 1–3 y, 900 µg RAE at 4–8 y) risks hepatotoxicity and raised intracranial pressure; chronic vitamin D above UL causes hypercalcemia; zinc excess (>7 mg/d at 1–3 y) induces copper deficiency; fluoride excess causes fluorosis. Iron is the classic fatal overdose — treat all supplements as medications: locked storage, labeled dosing devices, and third-party-tested products when used. Megadose regimens, herbal products with adulterants, and weight-loss or bodybuilding supplements in adolescents warrant direct, nonjudgmental screening questions during every diet history.