Trace Elements and Metabolism

Trace Elements Overview - Tiny Titans Intro

• Definition: Minerals vital for health, needed in tiny amounts (<100 mg/day or <0.01% body weight).
  • Essential: Deficiency impairs physiological functions (e.g., Fe, Zn, I, Se, Cu).
  • Non-essential: No defined biological role.
  • Toxic: All can be toxic at high intakes; some have narrow optimal/toxic range.
• General Functions:
  • Enzyme cofactors (catalytic roles).
  • Structural components of proteins (e.g., zinc fingers).
  • Hormone structure/action (e.g., iodine in thyroid hormones).

⭐ Most trace elements function as cofactors for enzymes, vital for metabolic pathways.

Iron Metabolism - Rusty Regulator

• Sources: Heme (meat, poultry, fish - readily absorbed), Non-heme (plants, dairy - $Fe^{3+}$ needs reduction to $Fe^{2+}$ by DcytB).
• Absorption (Duodenum): Apical uptake of $Fe^{2+}$ via DMT1. Basolateral export via Ferroportin (FPN1), then $Fe^{2+} \rightarrow Fe^{3+}$ (Hephaestin).

• Transport: $Fe^{3+}$ binds Transferrin in blood.
• Storage: Ferritin (primary, soluble), Hemosiderin (insoluble, in overload).
• Functions: O₂ transport (Hb, Mb), cytochromes (ETC), catalase, peroxidases.
• Deficiency (IDA): Microcytic hypochromic anemia; Plummer-Vinson syndrome. Labs: ↓Serum Fe, ↓Ferritin (<30 ng/mL), ↓% Saturation, ↑TIBC.
• Overload (Hemochromatosis): ↑Serum Fe, ↑Ferritin, ↑% Saturation.

  ⭐ Hepcidin is the master regulator of iron homeostasis, primarily by inhibiting ferroportin.

Zinc & Copper - Catalytic Couple

• Zinc (Zn):
  • Functions: Enzyme cofactor (Carbonic anhydrase, ALD, ALP, DNA/RNA pol, SOD).
  • Deficiency: Acrodermatitis Enteropathica (rash, alopecia), ↓wound healing, hypogonadism, anosmia.
    • 
  • Toxicity: Gastric distress, ↓Cu absorption.
• Copper (Cu):
  • Absorption: ATP7A (📌 Menkes: ATP7A - Absorption).
  • Transport: Ceruloplasmin.
  • Functions: Enzyme cofactor (Cyt c oxidase, Lysyl oxidase, Tyrosinase, SOD, Dopamine β-hydroxylase).
  • Toxicity: Wilson's Disease (ATP7B defect; 📌 ATP7B - Biliary excretion).
    • Features: ↓Ceruloplasmin, ↑Urinary Cu, Kayser-Fleischer rings.
    • 
• Zn-Cu Interaction: High Zn intake ↓ Cu absorption.

Iodine & Selenium - Thyroid Team-Up

• Iodine:
  • Sources: Iodized salt, seafood, dairy.
  • Function: Essential for thyroid hormone ($T_3, T_4$) synthesis.
  • Deficiency: Goiter, cretinism (children), myxedema (adults).
  • Wolff-Chaikoff effect: Excess iodine temporarily ↓ thyroid synthesis.
  • Jod-Basedow phenomenon: Iodine-induced hyperthyroidism.
• Selenium:
  • Sources: Brazil nuts, seafood, meat.
  • Function: Key for glutathione peroxidase (antioxidant) & deiodinases; converts $T_4 \xrightarrow{\text{Deiodinase (Se)}} T_3$.
  • Deficiency: Keshan disease (cardiomyopathy), Kashin-Beck disease (osteoarthritis).
  • Toxicity: Selenosis (garlic breath, hair loss).

⭐ Selenium is crucial for converting inactive T4 to active T3 via deiodinases.

Other Key Players - Mighty Minis Mix

• Manganese (Mn): Cofactor for enzymes like Superoxide Dismutase (SOD) & pyruvate carboxylase. Toxicity can cause manganism (Parkinson-like features).
• Chromium (Cr): Key component of Glucose Tolerance Factor (GTF), potentiates insulin action.

  ⭐ Chromium deficiency can lead to impaired glucose tolerance.

• Molybdenum (Mo): Cofactor for xanthine oxidase and sulfite oxidase. Deficiency is rare.
• Fluoride (F): Important for bone and teeth structure; prevents dental caries. Excess causes fluorosis.
• Cobalt (Co): Integral component of Vitamin B12 (cobalamin).

High‑Yield Points - ⚡ Biggest Takeaways

• Zinc: Cofactor for carbonic anhydrase, alkaline phosphatase; deficiency: acrodermatitis enteropathica, poor healing.
• Copper: For cytochrome c oxidase, lysyl oxidase; Menkes disease (↓Cu), Wilson's disease (↑Cu).
• Selenium: In glutathione peroxidase, thyroid deiodinases; deficiency: Keshan disease (cardiomyopathy).
• Chromium: Potentiates insulin (as GTF); deficiency: impaired glucose tolerance.
• Iodine: For thyroid hormone (T3/T4) synthesis; deficiency: goiter, cretinism.
• Manganese: Cofactor for mitochondrial SOD, pyruvate carboxylase; toxicity: manganism.