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Vitamin D deficiency in children

SNOMED: 34713006733 words•Updated 03/03/2026
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Exam Tips

  • In UK exams, remember thresholds: 25(OH)D <25 nmol/L = deficiency; 25-50 nmol/L = possible insufficiency; >50 nmol/L usually adequate.
  • Classic rickets triad to recall: bone deformity (bowed legs/wrist widening), biochemical pattern (high ALP, low phosphate, high PTH), and metaphyseal cupping/fraying on X-ray.
  • High-risk vignette pattern: darker skin + low sun exposure + breastfed infant without supplements.
  • Always mention emergencies: hypocalcaemic seizures and rare infant cardiomyopathy require urgent calcium-based management.

Definition

Vitamin D deficiency in children is a disorder of calcium-phosphate and skeletal mineral metabolism caused by inadequate vitamin D supply, impaired absorption, or reduced activation. In UK practice it is defined biochemically by serum 25-hydroxyvitamin D below 25 nmol/L (deficient), with 25-50 nmol/L often considered insufficient, and can lead to rickets, hypocalcaemia, and long-term failure to achieve optimal peak bone mass.

Pathophysiology

Vitamin D (cholecalciferol/ergocalciferol) is hydroxylated in the liver to 25(OH)D, then in the kidney to active 1,25(OH)2D under parathyroid hormone (PTH) control. Deficiency reduces intestinal calcium and phosphate absorption, causing secondary hyperparathyroidism, renal phosphate wasting, and increased bone resorption to maintain serum calcium. In growing children this impairs growth-plate mineralization (rickets) and increases unmineralized osteoid (osteomalacia pattern), producing bone pain, deformity, and proximal myopathy. In severe cases, rapid calcium demand (infancy/puberty) precipitates symptomatic hypocalcaemia (tetany/seizures), and very rarely hypocalcaemic dilated cardiomyopathy.

Risk Factors

  • Low sunlight exposure in the UK (especially winter), housebound lifestyle, or clothing that markedly limits skin exposure
  • Darker skin pigmentation (for example African, African-Caribbean, South Asian ancestry)
  • Exclusive breastfeeding without adequate vitamin D supplementation, particularly if maternal vitamin D status is low
  • Infants older than 6 months taking less than 500 mL/day of formula milk
  • Malabsorption states (coeliac disease, cystic fibrosis, Crohn's disease) or post-bariatric/intestinal surgery
  • Severe liver disease, nephrotic syndrome, or end-stage chronic kidney disease
  • Obesity (BMI >98th centile for age/sex)
  • Drugs that lower vitamin D bioavailability or increase catabolism (for example carbamazepine, phenytoin, phenobarbital, rifampicin, glucocorticoids, orlistat, colestyramine)

Clinical Features

Symptoms

  • Bone pain or tenderness (limbs, pelvis, back)
  • Muscle aches and proximal weakness (difficulty climbing stairs/rising from floor)
  • Delayed motor milestones or delayed walking
  • Irritability, cramps, tetany, or seizures in hypocalcaemia
  • Fatigue and reduced exercise tolerance

Signs

  • Bowed legs (genu varum) or knock knees (genu valgum)
  • Wrist widening/swelling from metaphyseal expansion (see radiographic figure of metaphyseal cupping/fraying in paediatric wrist films)
  • Rachitic rosary (costochondral swelling)
  • Craniotabes, frontal bossing, delayed fontanelle closure in infants
  • Waddling gait, growth faltering, dental enamel defects or delayed tooth eruption

Investigations

Serum 25-hydroxyvitamin D:<25 nmol/L supports deficiency; 25-50 nmol/L may indicate insufficiency; >50 nmol/L generally adequate for bone health
Bone profile (adjusted calcium, phosphate, alkaline phosphatase):Often low/low-normal calcium, low phosphate, raised ALP in active rickets
Parathyroid hormone (PTH):Usually elevated (secondary hyperparathyroidism)
Urea/creatinine, liver profile, magnesium:Assesses renal/hepatic contributors and coexisting electrolyte disturbance
X-ray (wrist/knee if rickets suspected):Metaphyseal cupping, fraying and splaying; osteopenic appearance in established disease
ECG (if symptomatic hypocalcaemia):May show prolonged QT interval

Management

Lifestyle Modifications

  • Age-appropriate safe sunlight exposure advice plus dietary optimisation (oily fish, egg yolk, fortified foods)
  • Correct modifiable risks: adherence support, weight management where appropriate, and review of interacting medicines
  • Long-term maintenance supplementation is usually required after correction, especially in persistent risk groups

Pharmacological Treatment

Vitamin D replacement (oral)

  • Colecalciferol (vitamin D3) prophylaxis: 8.5-10 micrograms (340-400 units) once daily in infants under 1 year
  • Colecalciferol (vitamin D3) prophylaxis: 10 micrograms (400 units) once daily in children 1-18 years
  • Colecalciferol treatment regimens for confirmed deficiency: commonly higher-dose daily courses in BNFC (product- and age-specific), then step-down to maintenance 400-1000 units daily

Use licensed paediatric preparations where possible; check baseline calcium/phosphate/ALP/PTH and recheck response after treatment phase. Avoid over-replacement due to hypercalcaemia risk; caution in renal stones, severe renal impairment, granulomatous disease, and primary hyperparathyroidism.

Calcium supplementation

  • Calcium carbonate or equivalent oral calcium when dietary intake is low or hypocalcaemia coexists
  • Calcium gluconate 10% IV for acute symptomatic hypocalcaemia (specialist/emergency setting; weight-based paediatric dosing)

Cardiac monitoring is required with IV calcium. Correct magnesium if low, as refractory hypocalcaemia may persist until magnesium is replaced.

Activated vitamin D (specialist use)

  • Alfacalcidol or calcitriol in selected children with CKD or impaired vitamin D activation

Reserved for specific indications under specialist supervision; monitor calcium and phosphate closely to avoid nephrocalcinosis and hypercalcaemia.

Complications

  • Nutritional rickets with limb deformity and impaired linear growth
  • Osteomalacia pattern with chronic bone pain and proximal muscle weakness
  • Increased fracture risk in radiologically active rickets
  • Hypocalcaemic tetany or seizures (classically infancy/adolescence)
  • Rare hypocalcaemic dilated cardiomyopathy and heart failure in infants
  • Failure to achieve optimal peak bone mass in adolescence

Prognosis

Most children improve well with prompt biochemical correction, treatment of underlying causes, and sustained prevention measures. Delayed diagnosis increases risk of persistent deformity and recurrent hypocalcaemia, so follow-up (clinical, biochemical, and sometimes radiographic) is important to confirm healing and prevent relapse.

Sources & References

💊BNF Drug References(7)

✅NICE Guidelines(1)

📖Textbook References(20)

  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1806, 1807)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 917)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1304)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 914, 915)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 194)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 915, 916)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1176)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 818)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1758)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1236)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 194)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1758)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1237)[context]
  • Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 320)[context]
  • Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 993)[context]
  • Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 993, 994)[context]
  • Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 993)[context]
  • Guyton and Hall Textbook of Medical Physiology (John E. Hall, Michael E. Hall) (Z-Library).pdf(pp. 994)[context]
  • Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 576, 577)[context]
  • Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 576, 577)[context]

Sources

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