8.3 Micronutrient Deficiencies (Rickets, Iron Deficiency)

Micronutrient deficiencies are especially examinable in the Arab region: vitamin D deficiency and rickets are common in breastfed infants with limited sun exposure or consistent covering, and iron deficiency peaks during the complementary-feeding transition at 9-24 months. ABHS items frequently test prevention doses, laboratory discrimination (Mentzer index, ferritin), and neurologic clues that separate vitamin B12 from folate deficiency.

Vitamin D Deficiency and Rickets

Vitamin D is essential for intestinal calcium and phosphate absorption and for bone mineralization. Deficiency in growing children causes rickets - defective mineralization of the growth plate and osteoid.

Risk Factors

• Exclusively breastfed infants who do not receive vitamin D supplementation (breast milk is naturally low in vitamin D)
• Dark skin pigmentation, limited sun exposure, or infants and children who are consistently covered or veiled (reduced cutaneous vitamin D synthesis)
• Prematurity and maternal vitamin D deficiency during pregnancy
• Malabsorptive conditions (for example, celiac disease, cystic fibrosis)

Clinical Presentation

Findings vary by age. In young infants, look for craniotabes (a soft, ping-pong-ball-like skull on palpation), delayed closure of the anterior fontanelle, and hypotonia (a floppy infant). In older infants and toddlers: rachitic rosary (palpable or visible swelling at the costochondral junctions), Harrison groove (a horizontal chest wall indentation at the diaphragm insertion), widened and cupped wrists and ankles, and genu varum (bowing of the legs) once weight-bearing begins. Growth failure, delayed motor milestones, delayed tooth eruption, and dental enamel defects may also occur. Severe hypocalcemia from vitamin D deficiency can present dramatically with seizures or tetany, sometimes as the initial presentation in infancy.

Laboratory and Radiographic Findings

Treatment and Prevention

Treatment is vitamin D repletion, using ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3), given either as a daily regimen or a single high-dose bolus regimen depending on local protocol, plus calcium supplementation if the child is hypocalcemic or has low dietary calcium intake. Prevention is the more heavily tested concept: all exclusively or partially breastfed infants should receive 400 IU/day of vitamin D, starting in the first few days of life, continued until the infant is consuming at least 1 liter/day of vitamin D-fortified formula or milk.

Iron Deficiency Anemia

Iron deficiency is the most common nutritional deficiency in children worldwide, with peak incidence between 9 and 24 months of age - precisely when rapid growth outpaces dietary iron intake if complementary feeding is inadequate.

Risk Factors

• Prematurity or low birth weight (reduced iron stores at birth, since most fetal iron transfer occurs in the third trimester)
• Exclusive breastfeeding beyond 6 months without iron-rich complementary foods or supplementation
• Early or excessive cow's milk intake before 12 months (low iron content plus occult gastrointestinal blood loss)
• Prolonged bottle use, low socioeconomic status, and lead exposure, which often co-occurs with iron deficiency and worsens its neurodevelopmental effects

Clinical Features

Mild cases are often asymptomatic and detected on routine screening. More significant deficiency causes pallor, fatigue, irritability, pica (including pagophagia, craving or eating ice), tachycardia, and, if prolonged, impaired cognitive and motor development.

Laboratory Findings

Iron deficiency anemia is a microcytic, hypochromic anemia:

• Ferritin: low - the most sensitive and specific marker of iron stores, but it is an acute-phase reactant and can be falsely normal or elevated with concurrent inflammation
• Serum iron: low; total iron-binding capacity (TIBC): elevated; transferrin saturation: low
• RDW (red cell distribution width): elevated, an early finding reflecting increasing variability in red cell size
• Peripheral smear: microcytic, hypochromic red cells

A key exam discrimination is separating iron deficiency anemia from beta-thalassemia trait, both of which cause microcytosis. The Mentzer index (MCV divided by RBC count) helps: a value greater than 13 favors iron deficiency (few, small cells - both RBC count and MCV are reduced), while a value less than 13 favors thalassemia trait (normal or increased RBC count with low MCV, because red cell production itself is not impaired - only globin synthesis is abnormal). RDW is typically elevated in iron deficiency but normal in thalassemia trait.

Treatment

First-line treatment is oral ferrous sulfate (elemental iron, roughly 3-6 mg/kg/day divided), ideally given with a source of vitamin C to enhance absorption and away from milk or tea, which inhibit iron absorption. A reticulocyte response within 5-7 days confirms an adequate response to therapy, and hemoglobin should rise by about 1 g/dL over 4 weeks. Iron therapy is continued for 2-3 months after hemoglobin normalizes to replete body iron stores, alongside dietary counseling to limit cow's milk intake to under 24 oz per day.

Other Clinically Relevant Micronutrient Deficiencies

Vitamin A deficiency is the leading preventable cause of childhood blindness worldwide. The earliest symptom is night blindness, progressing to xerophthalmia (dry conjunctiva and cornea), Bitot spots (foamy, triangular conjunctival patches), and, if untreated, corneal ulceration and keratomalacia. Vitamin A deficiency also increases the severity and mortality of measles and diarrheal illness, which is why high-dose vitamin A is given as part of measles treatment in deficient populations.

Vitamin B12 deficiency in infancy classically occurs in exclusively breastfed infants of mothers who are themselves B12-deficient (for example, a strict vegan diet or untreated pernicious anemia) or from malabsorption (terminal ileal disease). It causes a macrocytic, megaloblastic anemia - but unlike folate deficiency, it also causes neurologic findings: hypotonia, developmental regression or delay, irritability, and involuntary movements, because vitamin B12 is required for myelin synthesis.

Folate deficiency also produces a macrocytic, megaloblastic anemia but without neurologic findings - the key exam differentiator from vitamin B12 deficiency. Causes include poor dietary intake, malabsorption, and certain anticonvulsants (for example, phenytoin).

Zinc deficiency causes growth failure, immune dysfunction, poor appetite, and a perioral, perianal, or acral dermatitis; it is common in regions with plant-based, low-bioavailability diets and in children with malabsorption or severe acute malnutrition. Iodine deficiency remains relevant in iodine-insufficient regions and causes endemic goiter; severe deficiency in pregnancy or early infancy causes cretinism (intellectual disability, deafness, and growth failure). Universal iodized salt programs are the cornerstone of prevention.

Exam Trap: Macrocytic anemia plus neurologic signs (hypotonia, developmental regression) in a breastfed infant should suggest maternal vitamin B12 deficiency, especially with a vegan maternal diet. Macrocytic anemia alone, without neurologic findings, should suggest folate deficiency.