1Biochemistry and Metabolic Storage
Vitamin A is an umbrella term for a family of fat-soluble retinoids — retinol, retinal, retinoic acid, and retinyl esters — as well as provitamin A carotenoids (principally beta-carotene) found in plant foods. Each form has distinct metabolic roles: retinal is the chromophore in rhodopsin (night vision); retinoic acid is the transcriptionally active form that governs epithelial differentiation and immune programming; retinyl esters are the storage form.
Approximately 80–90% of the body's retinol is stored in hepatic stellate (Ito) cells as retinyl palmitate. Under adequate nutrition, these stores can sustain normal function for 3–6 months. Retinol is transported in plasma bound to retinol-binding protein (RBP), which is coupled to transthyretin; as a result, protein malnutrition invariably depresses serum retinol independent of actual hepatic stores — a critical diagnostic trap.
| Metric | Normal | Subclinical Deficiency | Severe Deficiency |
|---|---|---|---|
| Serum Retinol | ≥1.05 μmol/L | 0.70–1.05 μmol/L | <0.35 μmol/L |
| Night Blindness | Absent | May be present | Present |
| Corneal risk | None | Low | High (keratomalacia) |
| Immune compromise | Normal | Modest | Marked (measles mortality ↑) |
Units used in clinical practice: 1 IU = 0.3 mcg retinol (RE). Beta-carotene from food is converted at a 12:1 ratio (12 mcg beta-carotene → 1 mcg RE). Supplement beta-carotene converts at 6:1.
2Xerophthalmia — WHO Grading and Treatment
Xerophthalmia is the leading preventable cause of childhood blindness globally. The WHO classifies it into a spectrum from functional (reversible) to structural (potentially irreversible) ocular damage:
The WHO Three-Dose Treatment Protocol
For any clinical stage of xerophthalmia (XN through X3), the WHO mandates an immediate high-dose three-dose schedule. The rationale is two-fold: the Day 0 and Day 1 doses rapidly saturate serum retinol; the Day 14 dose replenishes hepatic stores to prevent relapse.
| Age Group | Day 0 (Immediate) | Day 1 | Day 14 / Follow-up |
|---|---|---|---|
| Infant < 6 months | 50,000 IU | 50,000 IU | 50,000 IU |
| Infant 6–12 months | 100,000 IU | 100,000 IU | 100,000 IU |
| Child > 12 months / Adult | 200,000 IU | 200,000 IU | 200,000 IU |
| Pregnant (xerophthalmia only) | 10,000 IU/day | Or 25,000 IU/week × 4 weeks — do NOT exceed | |
3Vitamin A in Measles — Why It Is Mandatory
Measles virus infection causes a transient but profound depletion of vitamin A through multiple mechanisms: increased metabolic demand, urinary loss of RBP, and impaired hepatic mobilisation due to acute phase response. This creates a vicious cycle — vitamin A deficiency worsens measles complications (pneumonia, diarrhoea, encephalitis), and measles worsens vitamin A status.
The WHO and American Academy of Pediatrics (AAP) mandate vitamin A supplementation for all children with acute measles, regardless of baseline nutritional status or country of origin. Meta-analyses show that vitamin A supplementation in measles reduces all-cause mortality by 60–87% in vitamin A–deficient populations.
Measles Two-Dose Protocol
| Age | Day 0 | Day 1 | Day 14 (add if xerophthalmia) |
|---|---|---|---|
| Infant < 6 months | 50,000 IU | 50,000 IU | 50,000 IU |
| Infant 6–12 months | 100,000 IU | 100,000 IU | 100,000 IU |
| Child > 12 months | 200,000 IU | 200,000 IU | 200,000 IU |
4Routine Prophylaxis in Endemic Regions
The WHO recommends universal vitamin A supplementation for children 6–59 months in countries where vitamin A deficiency is a public health problem (serum retinol <0.70 μmol/L in >20% of children). This covers most of sub-Saharan Africa, South and Southeast Asia.
| Age | Dose | Frequency | Notes |
|---|---|---|---|
| Neonates (birth, if at risk) | 50,000 IU | Once at birth | For HIV-exposed infants and high-deficiency settings |
| Infants 6–12 months | 100,000 IU | Every 6 months | Delivered with EPI / immunisation visits |
| Children 12–59 months | 200,000 IU | Every 6 months | Standard WHO VASD programme |
| Postpartum women | 200,000 IU | Once within 6 weeks postpartum | Improves breast milk retinol; do NOT give in pregnancy |
5Chronic Malabsorption Syndromes
In high-income countries, vitamin A deficiency is overwhelmingly secondary to fat malabsorption rather than dietary deficiency. Fat-soluble vitamins require intact micelle formation (bile salts), pancreatic lipase activity, and an adequate absorptive surface area — all compromised in chronic malabsorptive states:
| Condition | Mechanism | Typical Daily Dose | Formulation |
|---|---|---|---|
| Cystic Fibrosis | Exocrine pancreatic insufficiency; reduced bile acid secretion | 1,500–10,000 IU/day (age & PERT-adjusted) | Water-miscible preferred |
| Primary Biliary Cholangitis / Cholestasis | Bile acid deficiency → impaired micelle formation | 10,000–25,000 IU/day (monitor levels) | Water-miscible essential |
| Roux-en-Y Gastric Bypass | Bypassed proximal small bowel (primary absorption site) | 10,000 IU/day minimum; up to 50,000 IU 3×/week | Dry form / water-miscible |
| Sleeve Gastrectomy | Reduced gastric acid + altered transit | 5,000–10,000 IU/day | Standard oral |
| Coeliac Disease / IBD | Reduced mucosal absorptive surface | 5,000–10,000 IU/day (until remission) | Standard; water-miscible if severe |
| Short Bowel Syndrome | Massively reduced absorptive area | Monitor serum retinol; dose individually | IM/IV if enteral not tolerated |
6Pregnancy and Teratogenicity
Vitamin A occupies a uniquely important position in pregnancy safety: it is both essential for fetal development and teratogenic in excess. Retinoic acid regulates Hox gene expression — critical for craniofacial and central nervous system development. In excess, it causes cranial neural crest defects, cardiac outflow anomalies, and thymic aplasia.
| Dose | Safety in Pregnancy |
|---|---|
| RDA: 770 mcg RE (2,567 IU) | ✅ Safe — required for normal fetal development |
| Up to 3,000 mcg RE (10,000 IU)/day | ✅ Generally safe in most guidelines (WHO tolerable UL) |
| 10,000–25,000 IU/day for deficiency | ⚠️ Only if clinical xerophthalmia confirmed — short course |
| >25,000 IU/week | ❌ Avoid unless active xerophthalmia — teratogenic risk |
| 50,000–200,000 IU (treatment doses) | ❌ CONTRAINDICATED in pregnancy except active xerophthalmia |
| Beta-carotene (any dose) | ✅ Safe — conversion is tightly regulated; no teratogenic risk |
7Hypervitaminosis A — Acute and Chronic Toxicity
Acute Toxicity
Occurs after a single massive dose (typically >200,000 IU in children or accidental ingestion): bulging fontanelle, pseudotumor cerebri, vomiting, lethargy, and subsequent skin desquamation.
Chronic Toxicity
Results from prolonged intake of ≥10× RDA: dry peeling pruritic skin, alopecia, bone pain (cortical hyperostosis), premature epiphyseal closure in children, hepatomegaly, and hypercalcaemia.