Describe briefly about Vitamin A and vitamin d with information about synthesis , storage , uses, deficiency’s, symptoms, dosage , complications from Nelson and all the recent advances , guidelines from WHO,aap,iap, pubmed
"vitamin A" AND deficiency AND children
"vitamin D" AND deficiency AND children
WHO AAP IAP vitamin A vitamin D guidelines 2024 2025 children supplementation
"vitamin D" AND supplementation AND guidelines
vitamin A deficiency xerophthalmia Bitot spots night blindness
This composite figure illustrates the clinical and diagnostic progression of severe xerophthalmia and keratomalacia secondary to vitamin A deficiency in a 70-year-old male. Panels A, E, and G show clinical photographs highlighting characteristic Bitot's spots (foamy keratinized conjunctival plaques), corneal stromal infiltrates, and advanced keratomalacia with focal bulging (staphyloma formation). Panels B, D, F, H, and J utilize Anterior Segment Optical Coherence Tomography (AS-OCT) to quantify pathology, revealing conjunctival thickening (up to 737 μm), corneal stromal edema (1039 μm), and focal thinning (401 μm). Post-treatment panels (C, D, I, J) demonstrate clinical resolution after vitamin A supplementation and tectonic lamellar keratoplasty, with AS-OCT confirming successful graft adaptation. Histopathological sections (K, L) using HE and PAS stains contrast the diseased cornea against a normal control (M), showing massive epithelial hyperplasia (approximately 20 cell layers), focal keratinization, loss of Bowman's layer, and granular PAS-positive deposits, pathognomonic for squamous metaplasia in the setting of nutritional deficiency.
This composite image presents clinical photographs and Anterior Segment Optical Coherence Tomography (AS-OCT) findings in a case of severe keratomalacia associated with Vitamin A deficiency. Panels A-D focus on the right eye (OD). Panel A shows advanced corneal melting (keratomalacia) characterized by a bulging, whitish corneal surface completely overgrown by vascularized conjunctival tissue (conjunctivalization). Panel C highlights keratinization on the corneal surface, resembling Bitot's spots (arrow). Panels B and D provide AS-OCT cross-sections showing massive corneal thickening (940 μm), epithelial thickening (196 μm), and complete iris-to-cornea attachment (athalamia/anterior synechiae, arrow). Panels E and F focus on the left eye (OS). Panel E demonstrates bulbar conjunctival hyperemia and a hazy peripheral lesion at the 7-8 o'clock position (arrow). Panel F (AS-OCT) confirms slight peripheral corneal thinning to 556 μm in that same region (arrow). This series illustrates the range of ophthalmic manifestations of systemic malnutrition, from early peripheral thinning to end-stage keratectasia and corneal scarring.
This clinical photograph demonstrates the oral administration of high-dose vitamin A supplementation to a pediatric patient. The image shows an adult health worker or caregiver using a manual technique to ensure safe delivery: one hand gently stabilizes the child's jaw and depresses the lower lip to keep the mouth open, while the other hand squeezes a small capsule or dispenser. A single, translucent red droplet of the liquid supplement is captured in mid-air, directed toward the child's open mouth. The child, appearing to be an infant or toddler, has their mouth open wide, revealing the tongue and primary dentition. This visual illustrates a common public health intervention used in nutritional programs to prevent vitamin A deficiency (VAD) and its associated complications, such as xerophthalmia and increased susceptibility to infections. The focus is on the practical application and administration technique within a community health or pediatric clinical setting.
rickets vitamin D deficiency bowing legs bone changes children
This clinical photograph displays the classic musculoskeletal manifestations of vitamin D deficiency rickets in a young child. The most prominent feature is significant genu varum (bowing of the legs), where the weight-bearing long bones show lateral curvature due to impaired mineralization of the growth plate and osteoid matrix. Additionally, the child exhibits a distended abdomen (potbelly), which is a common clinical sign associated with rickets due to hypotonia of the abdominal muscles. The upper extremities appear thin, suggesting poor muscle development or nutritional deficiency. This archival image serves as a pedagogical tool for identifying systemic skeletal deformities resulting from metabolic bone disease. Key educational concepts include the relationship between vitamin D deficiency, calcium homeostasis, and the softening of bones (osteomalacia) during childhood development. The clinical relevance extends to pediatrics, endocrinology, and public health nutrition.
A clinical photograph of the lower extremities of a pediatric patient exhibiting signs of metabolic bone disease, likely rickets. The image demonstrates a prominent bilateral bowing of the legs (genu varum), characterized by a distinct outward curvature of the femoral and tibial shafts. There is marked enlargement and widening of the ankle joints, consistent with metaphyseal flaring. The skin over the affected regions appears intact without discoloration or acute inflammatory changes. This presentation is a classic clinical manifestation of vitamin D deficiency or hereditary rickets, illustrating the skeletal deformities that arise from impaired mineralization of the growth plates and osteoid matrix during development. The image serves as an educational tool for identifying physical signs of systemic pediatric bone pathology and understanding the orthopedic consequences of chronic mineral deficiencies.
This clinical photograph displays a 6.5-year-old boy (left) and his 4-year-old sister (right) presenting with characteristic skeletal manifestations of rickets, likely secondary to severe vitamin D deficiency. The boy exhibits genu valgum (knock-knees), characterized by inward angling of the knees, while the girl demonstrates significant genu varum (bow legs), showing a lateral outward curvature of the femurs and tibiae. Both children show evidence of growth retardation (short stature for age) and additional skeletal deformities, including potentially widened epiphyses at the wrists and ankles. The image serves as a classic educational example of how nutritional or metabolic bone diseases interfere with proper mineralization of the growth plate, leading to progressive softening and bowing of weight-bearing long bones during childhood development.
Vitamin A and Vitamin D - A Comprehensive Pediatric Review
VITAMIN A (Retinol)
Structure and Forms
- Retinol - the transport and storage form
- Retinal - the aldehyde form (used in vision)
- Retinoic acid - the active transcriptional form
- Retinyl esters - the storage form in the liver
- Provitamin A carotenoids - plant precursors (most important: β-carotene, which contributes ~30% of dietary vitamin A)
Synthesis and Metabolism
- Animal sources (preformed vitamin A): liver, fish, eggs, milk, butter
- Plant sources (provitamin A): yellow/leafy green vegetables - carrots, squash, spinach, broccoli
- Requires bile, pancreatic enzymes, and antioxidant activity in food
- Retinol (as retinyl ester) and β-carotene absorbed through the intestinal wall
- β-carotene is converted to retinol within intestinal cells
- Retinol is packaged into chylomicrons and transported to the liver
- Liver takes up retinol via the apolipoprotein E receptor
- >90% of body's vitamin A reserves stored in the liver, predominantly as retinyl ester in perisinusoidal (Ito/stellate) cells
- Hepatic reserves are sufficient for at least 6 months in a well-nourished person
- For transport from liver to periphery: retinol binds to Retinol-Binding Protein (RBP), which is synthesized in the liver
- RBP is recycled after retinol is delivered to target cells via cell-surface RBP receptors
- In target cells: retinol may be stored as retinyl ester or oxidized to retinoic acid
Functions
-
Vision (rhodopsin synthesis): Vitamin A is a component of rhodopsin (rod cells) and three iodopsins (cone cells). Synthesis of all four visual pigments is reduced in deficiency. Retinal combines with opsin protein to form these pigments.
-
Epithelial differentiation: Retinoic acid binds to Retinoic Acid Receptors (RARs), forming heterodimers with Retinoic X Receptors (RXRs). These RAR/RXR heterodimers bind to Retinoic Acid Response Elements (RAREs) in regulatory DNA, controlling genes encoding growth factor receptors, tumor suppressor proteins, and secreted factors. Without vitamin A, mucus-secreting columnar epithelium undergoes squamous metaplasia → keratinizing epithelium.
-
Metabolic effects: Retinoids inhibit adipogenesis and stimulate lipid breakdown. RXR can heterodimerize with PPARs and Vitamin D receptors.
-
Immune function: Vitamin A promotes regeneration of damaged epithelia and is required for optimal immune function. Supplementation reduces diarrhea morbidity by ~15% and mortality by ~30%. Reduces overall child mortality by 20-30% in deficient populations.
Deficiency
- Poor nutrition (most common globally)
- Fat malabsorption (celiac disease, Crohn's, ulcerative colitis)
- Bariatric surgery
- Continuous use of mineral oil laxatives
- Liver disease (reduces RBP synthesis)
- Protein-energy malnutrition (reduces RBP synthesis even with adequate hepatic stores)
Clinical Signs and Symptoms
| WHO Grade | Finding |
|---|---|
| XN | Night blindness (nyctalopia) - earliest sign |
| X1A | Conjunctival xerosis (dryness) |
| X1B | Bitot's spots (foamy, keratinized plaques on conjunctiva) |
| X2 | Corneal xerosis |
| X3A | Corneal ulceration/keratomalacia <1/3 cornea |
| X3B | Keratomalacia ≥1/3 cornea → blindness |
| XS | Corneal scar |
| XF | Xerophthalmic fundus |
Dosage - Treatment and Supplementation
| Age | Dose |
|---|---|
| <6 months | 50,000 IU/day PO × 2 days |
| 6 months to <1 year | 100,000 IU/day PO × 2 days |
| 1-5 years | 200,000 IU/day PO × 2 days |
- Infant: 1,500 IU/day
- Child 1-3 yr: 5,000 IU/day
- Child 4-8 yr: 5,000-10,000 IU/day
- Child ≥9 yr/adolescent: 10,000 IU/day
- RDA expressed in retinol equivalents (reflecting both preformed vitamin A and β-carotene)
- 900 mcg RAE/day for adult males; lower for children
Toxicity / Complications of Excess
- Headache, dizziness, vomiting, stupor, blurred vision
- May mimic brain tumor (pseudotumor cerebri/raised ICP, papilledema)
- Irritability, GI disturbance, rash
- Weight loss, anorexia, nausea, vomiting
- Bone and joint pain
- Increased osteoclast activity → bone resorption → fracture risk
- Hepatotoxicity (fibrosis, cirrhosis with very high doses)
- Skin changes (peeling, alopecia)
VITAMIN D (Calciferol)
Structure and Forms
- Vitamin D3 (Cholecalciferol): Endogenously synthesized in skin from 7-dehydrocholesterol under UV-B; also from animal dietary sources
- Vitamin D2 (Ergocalciferol): From plant sources (ergosterol); less potent than D3
- 25-hydroxyvitamin D [25(OH)D]: Circulating storage form; used for assessment of vitamin D status
- 1,25-dihydroxyvitamin D [1,25(OH)₂D = Calcitriol]: The biologically active form
Synthesis and Metabolism
- Solar UV-B irradiation converts 7-dehydrocholesterol in skin → Pre-vitamin D3 → (heat) → Cholecalciferol (D3)
- Melanin competes for UV-B; darker skin = reduced D3 production
- Deep-sea fish (salmon, tuna, mackerel), fish liver oils
- Egg yolks, fortified milk/dairy, mushrooms (UV-exposed)
- Plant sources contain ergosterol → vitamin D2
- Vitamin D (from skin or gut) binds to vitamin D-binding protein (DBP/α1-globulin) in plasma → transported to liver
- Liver 25-hydroxylase converts → 25(OH)D (the circulating storage form; half-life ~2-3 weeks)
- Kidney 1α-hydroxylase converts → 1,25(OH)₂D (Calcitriol) (the active form)
- Hypocalcemia → ↑PTH → activates 1α-hydroxylase → ↑1,25(OH)₂D
- Hypophosphatemia → directly activates 1α-hydroxylase
- High 1,25(OH)₂D → feedback inhibition of 1α-hydroxylase
Functions
- Intestine: Stimulates Ca²⁺ and HPO₄²⁻ absorption by upregulating calcium transport proteins in enterocytes
- Kidney: Stimulates Ca²⁺ reabsorption in distal tubules via calbindin, plasma membrane calcium pump, epithelial calcium channel
- Bone: Required for mineralization of osteoid matrix and epiphyseal cartilage; upregulates RANKL on osteoblasts → osteoclast activation → calcium/phosphate mobilization
- Parathyroid: High 1,25(OH)₂D decreases PTH gene transcription (negative feedback)
Deficiency
- Insufficient sunlight exposure (high latitudes, indoor lifestyle, dark skin, cultural clothing, sunscreen use)
- Dietary insufficiency
- Fat malabsorption (celiac disease, cholestatic liver disease, Crohn's disease, cystic fibrosis)
- Prematurity (vitamin D crosses placenta in last trimester only)
- Chronic kidney disease (impaired 1α-hydroxylation)
- Anticonvulsant drugs (phenytoin, phenobarbitone - interfere with gut absorption and alter metabolism)
- Vitamin D-dependent rickets Type I (inherited 1α-hydroxylase deficiency)
- Vitamin D-resistant rickets (renal tubular phosphate leak)
- Maternal vitamin D deficiency during pregnancy
| Status | 25(OH)D Level |
|---|---|
| Deficiency | <12 ng/mL (<30 nmol/L) |
| Insufficiency | 12-20 ng/mL (30-50 nmol/L) |
| Sufficiency | >20 ng/mL (>50 nmol/L) |
Clinical Signs and Symptoms
- Skeletal deformities from impaired bone mineralization:
- Craniotabes (ping-pong ball skull in infants)
- Frontal bossing, delayed fontanelle closure
- Rachitic rosary (beading at costochondral junctions)
- Harrison's sulcus (groove along lower thorax)
- Genu varum (bowing of legs) or genu valgum (knock-knees) in toddlers
- Widened wrists and ankles (metaphyseal flaring)
- Pathological fractures
- Hypocalcemia: Tetany, convulsions, laryngospasm, prolonged QTc
- Myopathy: Hypotonia, proximal muscle weakness, delayed walking
- Growth retardation
- Dental abnormalities: Enamel defects, delayed eruption
- Increased respiratory infections (hypotonia of respiratory muscles)
- Low/normal serum calcium
- Low serum phosphate
- Elevated alkaline phosphatase (hallmark)
- Low 25(OH)D
- Elevated PTH (secondary hyperparathyroidism)
- Widening and cupping/fraying of metaphyses
- Decreased bone density
- Bowing of long bones
- Bone pain (especially axial skeleton, lower limbs)
- Proximal myopathy, waddling gait
- Looser's zones (pseudofractures) on imaging
- Increased fracture risk (vertebral bodies, femoral necks)
- Histology: thickened layers of eosinophilic unmineralized osteoid around basophilic mineralized trabeculae
Dosage
- All breastfed infants: 400 IU/day starting within the first 2 months of life, continuing throughout childhood/adolescence
- Formula-fed infants consuming <500 mL/day fortified formula: also supplement 400 IU/day
| Population | Dose |
|---|---|
| Pregnant/lactating women | 600 IU/day |
| Breastfed infants (first year) | 400 IU/day from first few days of life |
| Children 1-3 years | 600 IU/day |
| Children 4-10 years | 600-1,000 IU/day |
| Adolescents | 600 IU/day |
- Children <1 year: 2,000 IU/day × 12 weeks
- Children >1 year: 3,000 IU/day × 12 weeks
- Children >3 years with confirmed deficiency: 60,000 IU once weekly × 6 weeks (stoss therapy)
- Children with malabsorption: higher doses as needed
| Age | Insufficiency (12-20 ng/mL) | Deficiency (<12 ng/mL) |
|---|---|---|
| <1 year | 1,000 IU once daily | 2,000-4,000 IU once daily |
| ≥1 year | 2,000 IU once daily | 5,000-6,000 IU once daily OR 50,000 IU once weekly |
- Age <10 yr: Insufficiency: 2,000 IU/day; Deficiency: 5,000 IU/day
- Age ≥10 yr: Insufficiency: 4,000-6,000 IU/day; Deficiency: 10,000 IU/day or 50,000 IU/week
Toxicity / Complications of Excess
- Hypercalcemia: nausea, vomiting, anorexia, weakness, constipation, polyuria, polydipsia
- Hypercalciuria → nephrolithiasis, nephrocalcinosis
- Metastatic calcification (soft tissues, blood vessels, kidneys, cornea, lungs)
- Raised serum 25(OH)D (typically >150 ng/mL or 375 nmol/L)
- Prolonged excess → renal failure
- Infants <6 months: 1,000 IU/day
- Infants 6-12 months: 1,500 IU/day
- Children 1-3 years: 2,500 IU/day
- Children 4-8 years: 3,000 IU/day
- Children >8 years/adults: 4,000 IU/day
RECENT ADVANCES AND GUIDELINE UPDATES (2023-2026)
Vitamin A - Recent Evidence
-
Measles management (2026): A systematic review (Kaur et al., 2026) confirmed that high-dose vitamin A supplementation remains a key therapeutic strategy in acute measles management, reducing severity, ocular complications, and mortality - especially in vitamin A-deficient populations. The WHO 2-dose regimen is strongly supported.
-
Neonatal respiratory outcomes (2024): A meta-analysis by Li et al. (2024) showed significant association between vitamin A status and neonatal respiratory diseases, suggesting supplementation may have a protective role in premature infants.
-
Pregnancy supplementation (2023): A meta-analysis (Ma et al., 2023) found that vitamin A supplementation during pregnancy improved birth weight and infant growth outcomes, particularly in deficient populations.
-
Biofortification: WHO and UNICEF continue to push crop biofortification (β-carotene-rich orange sweet potato, golden rice) as a sustainable strategy to address VAD in low-income countries.
Vitamin D - 2024 Endocrine Society Clinical Practice Guideline
- Does not recommend routine vitamin D screening in the general population
- Does not support supplementation for prevention of cardiovascular disease, diabetes, cancer, or autoimmune diseases (insufficient evidence)
- Does recommend supplementation to prevent rickets in infants and young children, and to prevent upper respiratory tract infections in children
- Supports empirical supplementation (without screening) in:
- Infants (400-600 IU/day)
- Children and adolescents (600-1,000 IU/day)
- Pregnant women
- Dark-skinned individuals at higher latitudes
- The guideline is controversial - a rebuttal (Nwosu, 2025) criticized the lack of specific guidance for preterm infants and downplaying of vitamin D's role in immune and metabolic health in children.
QUICK-REFERENCE COMPARISON TABLE
| Feature | Vitamin A | Vitamin D |
|---|---|---|
| Type | Fat-soluble, retinoid | Fat-soluble, secosteroid |
| Main form | Retinol (transport), Retinyl ester (storage) | Cholecalciferol (D3) → Calcitriol (active) |
| Endogenous synthesis | No | Yes (skin, UV-B) |
| Primary storage | Liver (Ito cells), >90% | Liver and adipose tissue |
| Activation | Oxidation to retinoic acid | Liver (25-OH) → Kidney (1,25-OH₂) |
| Key receptor | RAR/RXR nuclear receptors | VDR (nuclear receptor) |
| Classic deficiency disease | Xerophthalmia, night blindness | Rickets (children), Osteomalacia (adults) |
| First sign of deficiency | Night blindness | Hypocalcemia, craniotabes |
| Key lab marker | Serum retinol | Serum 25(OH)D |
| Deficiency treatment (child) | 200,000 IU × 2 days (measles) | 3,000 IU/day × 12 weeks (IAP) |
| Prophylaxis dose | Not routinely supplemented universally | 400 IU/day (infants, AAP/IAP) |
| Toxicity | Pseudotumor cerebri, teratogenicity | Hypercalcemia, nephrocalcinosis |
| Teratogenic | Yes (high dose - Category X) | No (at recommended doses) |
Key References
- Robbins & Kumar Basic Pathology, pp. 292-296 - primary source for metabolism, functions, deficiency pathology
- Harriet Lane Handbook (23rd ed., Johns Hopkins) - dosing tables
- Tietz Textbook of Laboratory Medicine (7th ed.) - lab assessment
- IAP Consensus on Vitamin D (PMC11964374) - Indian pediatric guidelines
- 2024 Endocrine Society CPG on Vitamin D (Pilz et al., 2026)
- Measles management systematic review (Kaur et al., 2026)
- Vitamin A in neonatal respiratory disease (Li et al., 2024)