Trace Minerals Exhaustive Study Notes

Overview of Trace Minerals

• Trace minerals are essential dietary minerals required by the body in very small amounts to maintain health and facilitate various physiological processes.

• This lecture, presented by Janine Grant for Bio 125 Distance Learning, covers the main functions, absorption mechanisms, metabolism, deficiency symptoms, and toxicity of nine key trace minerals:

  • Iron ($Fe$)

  • Zinc ($Zn$)

  • Copper ($Cu$)

  • Manganese ($Mn$)

  • Selenium ($Se$)

  • Iodide ($I$)

  • Chromium ($Cr$)

  • Fluoride ($F$)

  • Molybdenum ($Mo$)

Iron ($Fe$)

• General Characteristics:

  • Present in every cell within the human body.

  • The majority of iron is found as a component of hemoglobin in the blood, while some exists as myoglobin within muscle tissues.

• Dietary Sources:

  • Heme Iron: Derived from animal sources, including meat, fish, and poultry.

  • Non-Heme Iron: Derived from plant sources, eggs, and dairy products. Some iron can also be introduced to food via contamination from iron cookware.

• Absorption and Metabolism:

  • Forms: The reduced ferrous form ($Fe^{++}$) is significantly more effectively absorbed than the ferric form ($Fe^{+++}$).

  • Heme Absorption: Heme iron is cleaved from its food source and absorbed directly in the ferrous form. It is more bioavailable than non-heme iron.

  • Non-Heme Absorption: Vitamin C and stomach acid assist in converting ferric iron to the more absorbable ferrous form.

  • Inhibitors: Absorption can be impeded by oxalates, phytates, tannins, and low stomach acid.

  • Transport: Iron is transported in the blood by a protein called transferrin. Transferrin saturation is a key indicator of iron status. Blood transferrin delivers iron to the bone marrow.

  • Oxidation/Reduction: For transport, iron must be converted back to the ferric ($Fe^{+++}$) state, a process aided by the mineral copper.

  • Storage: Iron is stored as ferritin in the liver, spleen, bone marrow, and intestinal mucosa.

  • Excretion: Occurs through bleeding, feces, and sweat.

• Functions:

  • Oxygen Transport: Part of hemoglobin, which carries oxygen in the blood to cells.

  • Carbon Dioxide Removal: Facilitates the transport of $CO_2$ back from the cells.

  • Muscle Oxygenation: Myoglobin provides a direct supply of oxygen to muscle cells.

• Recommended Dietary Allowances (RDAs) for Adults:

  • Males: $8\,mg/day$

  • Females: $18\,mg/day$

  • Pregnancy: $27\,mg/day$

  • Post-menopause: $8\,mg/day$

• Deficiency:

  • Anemia: Hypochromic, microcytic anemia (characterized by small, pale red blood cells), also known as iron deficiency anemia.

  • Symptoms: Fatigue, impaired mental ability (particularly in children), cold intolerance, nail spooning, sore tongue, and canker sores.

• Toxicity:

  • Mechanisms: Damage occurs through oxidation and the formation of free radicals causing tissue damage.

  • Hemochromatosis: An inborn error of metabolism leading to excessive iron deposition in the liver and other tissues.

Zinc ($Zn$)

• General Characteristics:

  • The most abundant intracellular trace mineral.

  • Acts as a co-factor for approximately 300 different enzymes.

• Absorption and Metabolism:

  • Absorbed throughout the small intestine.

  • Efficiency of absorption increases when deficiency exists.

  • Zinc from animal protein sources is better absorbed.

  • Inhibitors: Phytates in grains (especially wheat bran) act as antinutrients and impede absorption.

  • Storage: Bound within the cell to metallothionein, a sulfur-containing protein.

  • Interactions: When zinc intake is high, the body produces more metallothionein, which can preferentially bind to copper, leading to potential copper deficiency.

• Functions:

  • Vitamin A Mobilization: Required to move Vitamin A from the liver.

  • Vision and Immunity: Indirectly supports these via its relationship with Vitamin A.

  • Gene Expression: Regulates cell division, gene expression, and fetal development.

  • Reproduction: Essential for sexual development and the synthesis of sperm cells.

  • Antioxidant Activity: Acts as a cofactor for one form of Superoxide Dismutase (SOD), a powerful cellular antioxidant.

  • Senses: Crucial for taste and smell perception, as well as appetite regulation.

  • Metabolism: Involved in carbohydrate metabolism, insulin function, and alcohol metabolism.

  • Synthesis: Required for the synthesis of protein, carbohydrates, fats, RNA, and DNA.

  • Eicosanoids: Cofactor for the enzyme that synthesizes $PGE1$.

• RDAs for Adults:

  • Males: $11\,mg/day$

  • Females: $8\,mg/day$

• Deficiency:

  • Symptoms: Poor growth, delayed sexual development, low sperm count, delayed wound healing, impaired immunity, hair loss, skin lesions/rashes, altered taste/smell, and anorexia.

  • Night Blindness: Resulting from impaired Vitamin A function.

  • Acrodermatitis Enteropathica: A genetic disorder affecting zinc absorption.

  • Global Prevalence: Common in regions where phytates/oxalates/tannins are high (e.g., areas where flat-breads are staples).

• Toxicity:

  • Supplemental Risks: Intakes of $50\,mg/day$ or more can inhibit copper absorption/metabolism.

  • Symptoms: Depressed immunity and gastrointestinal (GI) disturbances.

• Food Sources:

  • Protein-rich foods: Meat, shellfish, poultry, eggs, and beans.

Copper ($Cu$)

• Absorption and Metabolism:

  • Absorbed in the small intestine (approximately $30-40\%$ of dietary intake).

  • Inhibitors: Excess zinc (especially from supplements) and very high intake of Vitamin C can block absorption.

  • Phytates: Copper is less affected by phytates compared to zinc.

  • Transport: Most blood copper is bound to the protein ceruloplasmin.

• Functions:

  • Iron Metabolism: Ceruloplasmin is a copper-containing enzyme necessary for iron transport.

  • Antioxidant: Cofactor for a form of Superoxide Dismutase (SOD).

  • Enzymatic Catalysis:

    • Cross-linking of collagen in bone and connective tissue.

    • Synthesis of catecholamines (dopamine, epinephrine, norepinephrine).

    • Synthesis of myelin.

    • Formation of melanin (pigment).

• RDAs for Adults:

  • $900\,mcg/day$

• Deficiency:

  • Generally uncommon.

  • Can be caused by high zinc intake through the induction of extra metallothionein.

  • Symptoms: Anemia (secondary to iron transport issues), bone/connective tissue abnormalities, and changes in hair structure or color.

• Toxicity:

  • Occurs mostly through excessive supplementation or storing acidic food in copper containers.

  • Symptoms: Nausea, vomiting, and potential liver damage.

  • Wilson’s Disease: A genetic defect causing copper to accumulate dangerously in the liver and brain.

• Food Sources:

  • Organ meats, shellfish, nuts, seeds, grains, and tap water from copper plumbing.

Manganese ($Mn$)

• General Characteristics:

  • Involved in numerous enzymatic reactions throughout the body.

• Absorption and Metabolism:

  • Generally poorly absorbed.

  • Absorption rate increases when intake is low and decreases when intake is high.

  • Excretion: Excess manganese is excreted via the bile.

• Functions:

  • Antioxidant Protection: Component of Manganese Superoxide Dismutase ($MnSOD$), which is the primary antioxidant in the mitochondria (a site highly susceptible to oxidative stress).

  • Structural Support: Cofactor for enzymes in bone remodeling, collagen formation, and cartilage formation.

  • Metabolism: Plays a role in the metabolism of amino acids, carbohydrates, and cholesterol.

• Adequate Intake (AI) for Adults:

  • Males: $2.3\,mg/day$

  • Females: $1.8\,mg/day$

• Deficiency and Toxicity:

  • Deficiency (Uncommon): Poor growth, skeletal/nervous system abnormalities, reproductive issues, and poor wound healing.

  • Toxicity: Causes nervous system damage. Inhalation (industrial settings) is particularly toxic to the nervous system.

• Food Sources:

  • Nuts, whole grains, wheat germ, pineapple, and tea.

  • Soybeans: Contain very large, nearly borderline toxic amounts.

Selenium ($Se$)

• General Characteristics:

  • Found in foods attached to sulfur-containing amino acids (e.g., selenomethionine, selenocysteine).

  • Selenocysteine is a critical part of the glutathione peroxidase molecule.

• Absorption and Metabolism:

  • Mostly absorbed in the upper GI tract; excess is excreted in the urine.

• Functions:

  • Antioxidant: Part of glutathione peroxidase, which destroys peroxides to reduce free radical formation. Works synergistically with Vitamin E.

  • Thyroid Regulation: As the enzyme iodothyronine deiodinase, it converts thyroxine ($T_4$) to the active form, triiodothyronine ($T_3$).

• RDA for Adults:

  • $55\,mcg/day$ (Narrow margin of safety; Upper Limit is $400\,mcg/day$).

• Deficiency:

  • Keshan Disease: A cardiomyopathy identified in selenium-poor regions of China (likely linked to a virus).

  • Associated with heart disease, cancer, and immune dysfunction, though research does not support supplemental benefit in non-deficient individuals.

• Toxicity:

  • Occurs at intakes over $400\,mcg/day$.

  • Symptoms: Hair/nail loss, skin lesions, irritability, nervous system damage, and "garlic breath" (due to selenium's affinity for sulfur).

  • Chronic high doses can be fatal.

• Food Sources:

  • Fish, meat, oats, grains. Brazil nuts are highly variable and may contain toxic amounts depending on soil concentration.

Iodide ($I$)

• General Characteristics:

  • Occurs in foods as free iodine or iodide ions. Essential for life.

  • Abundant in the ocean but often lacking in inland soils.

• Absorption and Metabolism:

  • Easily absorbed from intestines; stored in the thyroid gland.

  • Regulation of uptake is managed by Thyroid Stimulating Hormone (TSH) from the pituitary gland.

• Functions:

  • Essential component of thyroid hormones ($T_4$ and $T_3$) which regulate all metabolic processes.

  • Thyroxine ($T_4$) contains tyrosine and iodide.

• RDA for Adults:

  • $150\,mcg/day$ (Increases to $175-200\,mcg/day$ for pregnant/lactating women).

• Deficiency:

  • Goiter: Enlargement of the thyroid gland due to continuous TSH stimulation without iodide availability.

  • Hypothyroidism: Sluggishness and weight gain.

  • Developmental Issues: Cretinism in offspring (if deficient during pregnancy) and mental retardation in infants.

  • Goitrogens: Compounds in foods like cabbage and soy that inhibit hormone synthesis when iodide intake is marginal.

• Toxicity:

  • Excessive supplementation can also cause goiter.

  • Symptoms: Rashes, nausea, headaches, allergic reactions, and heart palpitations.

• Food Sources:

  • Seafood, iodized salt, and vegetables from iodide-rich soil.

Chromium ($Cr$)

• General Characteristics:

  • The trivalent form ($Cr^{3+}$) is utilized by the body. The hexavalent form ($Cr^{6+}$) is an industrial carcinogen.

• Absorption and Metabolism:

  • $10-25\%$ is absorbed via active transport in the small intestine.

  • Transported to the liver via transferrin (competes with iron for binding).

  • Diets high in simple sugars promote chromium loss in urine.

• Functions:

  • Glucose Metabolism: Stabilizes blood glucose by activating insulin receptors and enhancing insulin binding.

  • Also involved in fat and protein metabolism via insulin's role.

• AI for Adults:

  • Males: $35\,mcg/day$

  • Females: $25\,mcg/day$

• Deficiency and Toxicity:

  • Deficiency: Impaired glucose tolerance, elevated cholesterol, and triglycerides.

  • Toxicity: Low risk from dietary chromium; some supplements (picolinate, nicotinate) are not recommended due to potential toxicity.

Fluoride ($F$)

• General Characteristics:

  • Ionic form of fluorine gas. Found primarily in teeth and bones.

• Functions:

  • Mineralization: Replaces the hydroxy ($OH$) group in hydroxyapatite crystals ($Ca$ and $P$) to form fluoroapatite.

  • This stabilizes bone minerals and hardens tooth enamel.

• AI and Limits:

  • Males: $4\,mg/day$

  • Females: $3\,mg/day$

  • Upper Limit (UL): $10\,mg/day$.

• Deficiency and Toxicity:

  • Deficiency: Tooth decay.

  • Fluorosis: Discoloration and pitting of teeth from excess intake during development.

  • High Doses: Above $20\,mg/day$ can cause gastroenteritis, vomiting, bone deformation, kidney damage, and thyroid dysfunction.

Molybdenum ($Mo$)

• Functions: Cofactor for enzymes catalyzing redox reactions:

  • Metabolism of sulfur-containing amino acids (cysteine, methionine).

  • Breakdown of nucleotides (purines) into uric acid.

  • Oxidation of acetaldehyde (toxic intermediate in alcohol detoxification).

• RDAs and Health Status:

  • RDA: $45\,mcg/day$.

  • Deficiency: Rare, may lead to brain damage.

  • Toxicity: High uric acid (Gout).

Other Trace Minerals

• Several other minerals are currently being assessed for their physiological roles, including:

  • Arsenic ($As$)

  • Boron ($B$)

  • Nickel ($Ni$)

  • Silicon ($Si$)

  • Vanadium ($V$)

Trace minerals are essential dietary minerals required in small amounts for various bodily functions. This lecture covers nine key trace minerals:

• Iron (Fe): Vital for oxygen transport, found in hemoglobin and myoglobin. Dietary sources include meat, fish, and beans. Deficiency leads to anemia while toxicity can cause tissue damage.

• Zinc (Zn): Abundant intracellular trace mineral, crucial for enzyme function and immune response. Sources include meat and shellfish. Deficiency results in impaired growth and immunity, while excess can inhibit copper absorption.

• Copper (Cu): Important for iron metabolism and antioxidant activity. Found in organ meats and shellfish. Deficiency is rare but can cause anemia; toxicity occurs with excessive supplementation.

• Manganese (Mn): Involved in enzymatic reactions and antioxidant protection. Sources include whole grains and nuts. Deficiency is uncommon; toxicity can damage the nervous system.

• Selenium (Se): Acts as an antioxidant and regulates thyroid hormones. Found in fish, meat, and grains. Deficiency can lead to Keshan disease; high intake can cause toxicity with symptoms like hair loss.

• Iodide (I): Essential for thyroid hormones. Sources include seafood and iodized salt. Deficiency leads to goiter and developmental issues; excess can also cause goiter.

• Chromium (Cr): Stabilizes blood glucose; found in whole grains and meats. Deficiency can impair glucose tolerance; toxicity from supplements is rare.

• Fluoride (F): Strengthens teeth and bones. Sources include fluoride-treated water and seafood. Deficiency leads to tooth decay; excessive intake can cause fluorosis.

• Molybdenum (Mo): Cofactor in metabolism; found in legumes and whole grains. Deficiency is rare; excessive intake may lead to high uric acid levels.

• Other minerals under evaluation include arsenic, boron, nickel, silicon, and vanadium.