Human Nutrition: Minerals

Introduction to Minerals

• Minerals are inorganic substances required by the body in small amounts.
• They function in various processes, including bone and tooth formation, fluid balance, nerve conduction, muscle contraction, signaling, and catalysis.
• Minerals are micronutrients required in mg or µg amounts.

Macrominerals

• Macrominerals are required by adults in amounts >100 mg/day.
• They include:
  • Calcium (Ca2+)
  • Phosphorus (P as inorganic phosphate)
  • Magnesium (Mg2+)
  • Sodium (Na+)
  • Chloride (Cl-)
  • Potassium (K+)

Calcium

• Ca2+ is the most abundant mineral in the body, with ~98% found in bones.
• The remainder is involved in processes such as signaling, muscle contraction, and blood clotting.
• Hypercalcemia can result from overproduction of parathyroid hormone (PTH).
• Hypocalcemia can result from a deficiency of PTH or vitamin D.

Phosphorus

• Free phosphate (Pi) is the most abundant intracellular anion.
• 85% of the body's phosphorus is in the form of inorganic hydroxyapatite.
• Phosphate is supplied as ATP for kinases and as Pi for phosphorylases.
• Hormonal regulation of serum levels of Ca2+ and Pi are primarily controlled by calcitriol and PTH.

Magnesium

• About 60% of the body's Mg2+ is in bone.
• The mineral is required by various enzymatic reactions, including phosphorylation by kinases and phosphodiester bond formation by DNA and RNA polymerases.
• Hypomagnesemia can result from decreased absorption or increased excretion of Mg2+.
• Hypermagnesemia can cause hypotension.

Sodium, Chloride, and Potassium

• These minerals maintain water balance, osmotic equilibrium, acid-base balance, and electrical gradients across cell membranes.
• Na+, K+, and Cl- are primarily intracellular and extracellular electrolytes, respectively.
• Hypernatremia, hyponatremia, hyperkalemia, and hypokalemia can occur due to imbalances in these minerals.

Microminerals (Trace Minerals)

• Microminerals are required by adults in amounts between 1 and 100 mg/day.
• They include:
  • Copper (Cu)
  • Iron (Fe)
  • Manganese (Mn)
  • Zinc (Zn)

Copper

• Cu is a key component of several enzymes, including ferroxidases.
• Dietary deficiency is uncommon.
• Menkes syndrome and Wilson disease are genetic disorders of Cu metabolism.

Iron

• Fe is a component of many proteins, including prolyl hydroxylase and hemoglobin.
• Fe is present in the electron transport chain and is toxic in its free form.
• Dietary Fe sources include animal and plant sources.
• Iron deficiency can result in a microcytic, hypochromic anemia.
• Excess iron can occur due to accidental ingestion or genetic defects, leading to iron overload.

Zinc

• Zn plays important structural and catalytic functions in the body.
• Zn fingers are super-secondary structures in proteins that bind to DNA and regulate gene expression.
• Enzymes require Zn for activity, including alcohol dehydrogenase and carbonic anhydrase.
• Severe deficiency is seen with a defect in the intestinal transporter for Zn.

Chromium and Fluorine

• Cr potentiates the action of insulin by an unknown mechanism.
• F (as fluoride) is added to water to reduce the incidence of dental caries.

Ultratrace Minerals

• Ultratrace minerals are required by adults in amounts <1 mg/day.
• They include:
  • Iodine (I)
  • Selenium (Se)
  • Molybdenum (Mo)

Iodine

• Iodine is utilized in the synthesis of thyroid hormones triiodothyronine (T3) and thyroxine (T4).
• Circulating iodide is taken up in the epithelial follicular cells of the thyroid gland.
• Iodine deficiency can result in goiter and hypothyroidism.
• Hyperthyroidism can result from over-ingestion of I-containing supplements or Graves disease.

Selenium

• Se is present in ~25 human proteins (selenoproteins) as a constituent of the amino acid selenocysteine.
• Selenoproteins include glutathione peroxidase, thioredoxin reductase, and deiodinases.
• Keshan disease is a cardiomyopathy caused by eating foods produced from Se-deficient soil.