Trace Minerals: Functions, Sources, Deficiency, and Toxicity

Trace Minerals

Definition and Importance

Trace minerals, also known as microminerals, are essential nutrients required by the body in small amounts (less than 20 mg per day). Despite their low concentration (less than 5 g in the body), they play critical roles in various physiological processes.

• Main trace minerals: Iron, Zinc, Selenium, Fluoride, Chromium, Copper, Iodine, Manganese, Molybdenum

• Amount in plants depends on soil mineral content.

Bioavailability

The absorption and utilization of trace minerals depend on several factors:

• Individual nutritional status

• Other foods eaten simultaneously

• Form of the mineral (chemical state)

• Presence of other minerals (competition or synergy)

• Minimal digestion required for absorption; some minerals (e.g., iron) are recycled in the body.

Functions

• Most trace minerals act as cofactors for enzymes (metalloenzymes).

• Assist hormone functions

• Provide structure for bones and teeth

• Maintain health of red blood cells

• Component of antioxidants

Deficiency and Toxicity

• Deficiencies and toxicities are difficult to determine.

• Recommended intakes and upper limits are challenging to establish due to individual variability.

Table: Trace Minerals - Functions, Needs, Sources, Toxicity, Deficiency

Trace Mineral	Metabolic Function	Daily Needs (19+ yrs)	Food Sources	Toxicity Symptoms/UL	Deficiency Symptoms	Interaction with Other Nutrients
Iron (Fe)	Hemoglobin/myoglobin, cytochromes, immune system	Women: 18 mg/day Men: 8 mg/day	Meat, fish, poultry, enriched grains	Constipation, nausea, vomiting, organ damage UL: 45 mg/day	Fatigue, microcytic anemia, poor immune function	Zinc, Calcium, Ascorbic acid
Copper (Cu)	Enzyme cofactor, iron metabolism, connective tissue, antioxidant enzymes	900 μg/day	Cocoa, shellfish, nuts, legumes	Anemia, liver damage UL: 10,000 μg/day	Anemia, impaired growth/development	Zinc
Zinc (Zn)	Cofactor for metalloenzymes, DNA/RNA synthesis, antioxidant	Women: 8 mg/day Men: 11 mg/day	Seafood, meat, whole grains	Nausea, vomiting, cramps, immune suppression UL: 40 mg	Skin rash, hair loss, delayed growth	Iron, Calcium, Copper, Protein, Phytates
Selenium (Se)	Component of antioxidant enzymes	55 μg/day	Meat, seafood, grains	Brittle hair/nails, garlic breath, nervous system damage UL: 400 μg	Muscle weakness, Keshan disease	Unknown
Fluoride (F)	Fluoroapatite in teeth/bones, enhances bone mineralization	Women: 3.1 mg/day Men: 3.8 mg/day	Fluoridated water, tea	Fluorosis in teeth/bones UL: 10 mg	Dental caries	Calcium
Chromium (Cr)	Enhances insulin response	Women: 20-25 μg/day Men: 30-35 μg/day	Pork, egg yolks, whole grains	Unknown; insufficient data for UL	Elevated blood glucose	Vitamin C, Phytates
Iodine (I)	Component of thyroid hormones	150 μg/day	Iodized salt, seafood, dairy	Thyroid dysfunction, hypothyroidism UL: 1,100 μg	Goiter, cretinism	Unknown
Molybdenum (Mo)	Cofactor for metalloenzymes	45 μg/day	Legumes, nuts, dairy, cereals	Unknown in humans UL: 2,000 μg	Unknown in humans	Unknown
Manganese (Mn)	Cofactor for metalloenzymes, carbohydrate metabolism	Women: 1.8 mg/day Men: 2.3 mg/day	Beans, oats, nuts, tea, vegetables	Abnormal central nervous system UL: 11 mg	Unknown in humans	Calcium, Iron, Phytates

Iron (Fe)

Forms and Sources

• Heme iron: Found in animal foods (meat, poultry, fish), part of hemoglobin and myoglobin, ferrous form ($Fe^{2+}$).

• Nonheme iron: Found in plant foods (grains, vegetables, enriched breads, cereals), ferric form ($Fe^{3+}$), 80% of dietary iron.

Bioavailability

• Heme iron is 2-3 times more bioavailable than nonheme iron.

• Nonheme iron absorption is reduced by oxalates (leafy vegetables) and polyphenols (tea, coffee).

• Absorption is enhanced by vitamin C and the MFP (meat, fish, poultry) factor.

Factors Influencing Iron Absorption

Enhance Iron Absorption	Decrease Iron Absorption
Sufficient hydrochloric acid in stomach The form of iron (heme > nonheme) Increased need (blood loss, pregnancy, growth) Vitamin C in small intestine Presence of MFP factor	Phytates in cereal grains Oxalates Polyphenols Reduced stomach acid Excess use of antacids Excess minerals (calcium, zinc, magnesium)

Absorption and Transport

• Regulated by the hormone hepcidin, which inhibits ferroportin from transporting iron out of enterocytes.

• Low iron stores increase absorption; high stores decrease absorption.

• Excess iron is excreted in feces.

• 95% of body iron is recycled, mainly from degraded hemoglobin.

Metabolic Functions

• Oxidation-reduction reactions

• Major component of hemoglobin and myoglobin (oxygen and carbon dioxide transport)

• Energy metabolism (cytochromes in mitochondria)

• Immune function (lymphocyte and macrophage production, antioxidant protection)

• Brain function (neurotransmitter synthesis: dopamine, epinephrine, norepinephrine, serotonin)

Daily Needs

• Women (19-50): 18 mg/day; after menopause: 8 mg/day

• Men: 8 mg/day

• Vegetarians: 1.8 times higher needs

Deficiency and Toxicity

• Deficiency: Iron-deficiency anemia (fatigue, weakness, reduced immunity); at-risk groups include pregnant women, menstruating women, infants, toddlers.

• Toxicity: Constipation, nausea, vomiting, diarrhea; upper level 45 mg/day; risk for those with liver disease, hemochromatosis (genetic iron overload), children (accidental poisoning).

• Excess iron may increase risk for heart disease and cancer due to free radical production.

Copper (Cu)

Forms and Absorption

• Exists as cupric ($Cu^{2+}$, oxidized) and cuprous ($Cu^{+}$, reduced) forms.

• Absorbed in the small intestine; bioavailability enhanced by amino acids, reduced by phytates, zinc, and other minerals.

Metabolic Functions

• Part of metalloenzymes (e.g., ceruloplasmin, which oxidizes iron)

• Energy production

• Connective tissue formation (collagen, elastin)

• Antioxidant defense (superoxide dismutase)

• Melanin synthesis

• Blood clotting and immune system maintenance

Daily Needs

• Adults: 900 μg/day

• Upper level: 10,000 μg/day

Deficiency and Toxicity

• Toxicity: Stomach pain, cramps, nausea, diarrhea, liver damage

• Deficiency: Rare; symptoms include fatigue, weakness; at-risk groups: premature infants, malnourished infants, those on IV feedings

• Genetic disorders: Menkes disease (copper transport disorder), Wilson's disease (copper excretion disorder)

Zinc (Zn)

Absorption and Transport

• Controlled at the small intestine; stored bound to metallothionein

• Transported in blood bound to albumin

• Absorption reduced by high nonheme iron, phytates, high-fiber diets; improved by animal proteins

• Recycled via pancreatic juices; excreted in feces, minor losses in urine, sweat, skin, hair

Metabolic Functions

• Wound healing

• DNA/RNA synthesis, gene regulation

• Immune system support (antioxidant, inflammation reduction)

• Enzyme/protein function (skin repair, taste perception)

• May prevent age-related macular degeneration

Daily Needs

• Women: 8 mg/day

• Men: 11 mg/day

• Vegetarians at higher risk for deficiency

Deficiency and Toxicity

• Toxicity: Upper level 40 mg/day; symptoms: stomach pain, nausea, vomiting, diarrhea; excess interferes with copper absorption, suppresses immunity, lowers HDL cholesterol

• Deficiency: Delayed growth, hair loss, appetite loss, impaired taste, diarrhea, delayed sexual maturation, impotence, skin rash

Additional Trace Minerals

Selenium (Se)

• Component of selenoproteins (enzymes)

• Antioxidant (glutathione peroxidase), thyroid hormone regulation

• May reduce cancer risk

• Daily need: 55 μg/day; UL: 400 μg/day

• Deficiency: Keshan disease (heart damage), thyroid changes

• Toxicity: Selenosis (brittle nails/hair, skin rash, nervous system damage)

Fluoride (F)

• Not essential, but critical for strong teeth (fluoroapatite formation)

• Reduces dental caries, increases bone mineral density

• Daily need: Women 3.1 mg/day, Men 3.8 mg/day; UL: 10 mg/day

• Deficiency: Dental caries; Toxicity: Fluorosis

Chromium (Cr)

• Enhances insulin effectiveness, may improve glucose metabolism

• Daily need: Women 20-25 μg/day, Men 30-35 μg/day; no established UL

• Deficiency: Rare, may increase blood glucose/fatty acids

• Toxicity: No known risks from food/supplements

Iodine (I)

• Essential for thyroid hormone synthesis (thyroxine, triiodothyronine)

• Regulates metabolic rate, reproduction, energy production, nerve/muscle/heart function

• Daily need: 150 μg/day; UL: 1,100 μg/day

• Deficiency: Goiter, cretinism (congenital hypothyroidism)

• Toxicity: Impaired thyroid function

Molybdenum (Mo)

• Cofactor for metalloenzymes (amino acid metabolism, redox reactions)

• Daily need: 45 μg/day; UL: 2,000 μg/day

• Deficiency: Not seen in healthy individuals

• Toxicity: Reproductive/kidney problems in animals

Manganese (Mn)

• Cofactor for enzymes (carbohydrate, fat, amino acid metabolism, bone/cartilage formation)

• Daily need: Women 1.8 mg/day, Men 2.3 mg/day; UL: 11 mg/day

• Deficiency: Rare; symptoms: rash, scaly skin

• Toxicity: Nervous system damage (Parkinson-like symptoms)

Other Minerals: Arsenic, Boron, Nickel, Silicon, Vanadium

These minerals may contribute to body functions but are not considered essential nutrients for humans.

• Arsenic: May be needed for amino acid metabolism in animals; no known toxicity from organic forms in food.

• Boron: May affect reproduction in animals; high amounts may cause problems; UL: 20 mg/day.

• Nickel: Essential for animals; no known human toxicity; UL: 1 mg/day for nickel salts.

• Silicon: May be needed for bone formation in animals; no known toxicity from food.

• Vanadium: Insulin-like actions in animals; excess may cause kidney damage; UL: 1.8 mg/day.

Nutrient-Deficiency Anemias

Definition and Classification

• Anemia: Blood lacks enough healthy, normal-sized red blood cells to deliver oxygen to tissues.

• Classified by red blood cell size:

  • Microcytic anemia: Small, pale red blood cells; most commonly caused by iron deficiency.

  • Macrocytic anemia: Large, abnormal red blood cells; most commonly caused by folate or vitamin B12 deficiency.

Iron-Deficiency Anemia

• Most common nutrient deficiency worldwide; higher risk in women.

• Causes: Blood loss (ulcers, cancers), insufficient intake, malabsorption.

• Symptoms: Fatigue, pale skin, irritability, shortness of breath, sore tongue, brittle nails, pica, headache, blue tinge to eyes, decreased appetite.

• Children: Risk of irreversible intellectual impairment.

• Diagnosis: Blood tests (CBC, total iron-binding capacity).

• Treatment: Iron supplements (ferrous sulfate, gluconate, fumarate); take with vitamin C, avoid milk/antacids.

Macrocytic and Pernicious Anemia

• Macrocytic anemia: Loss of appetite, sore mouth/tongue, shortness of breath, fatigue, heart palpitations, pale lips/eyelids; caused by folate or vitamin B12 deficiency.

• Diagnosis: Mean cell volume, serum folate, serum vitamin B12.

• Treatment: Folate or vitamin B12 supplements.

• Pernicious anemia: Inability to absorb vitamin B12 due to lack of intrinsic factor (often from gastritis or autoimmune attack on stomach cells); symptoms include diarrhea/constipation, pale skin, concentration problems, shortness of breath; treated with intramuscular vitamin B12 injections.