Trace Minerals: Iron Functions and Absorption

Study Notes

Trace Minerals

Trace minerals are essential for various bodily functions, although only needed in small amounts

Iron

Forms:
- Ferrous (Fe⁺⁺): Reduced form
- Ferric (Fe⁺⁺⁺): Oxidized form
Roles in the Body:
- Cofactor in oxidation-reduction reactions
- Component of hemoglobin (oxygen transport in blood)
- Component of myoglobin (oxygen storage in muscles)
- Energy utilization in cell metabolism
Absorption:
- Excess iron is stored in mucosal ferritin.
- When needed, iron is released to mucosal transferrin, which transfers it to the bloodstream.
- If not needed, iron is excreted in shed intestinal cells.
Forms in Food:
- Heme iron (animal source): High bioavailability, not affected by dietary factors.
- Nonheme iron (animal and plant sources): Bioavailability affected by dietary factors.
Factors Enhancing Nonheme Iron Absorption:
- MFP factor (meat, fish, poultry digestion)
- Vitamin C
- Citric acid
- Lactic acid
- HCI from stomach
- Sugars
Factors Inhibiting Nonheme Iron Absorption:
- Phytates
- Fibers
- Oxalates
- Calcium/Phosphorus
- Tannic acid
- EDTA
Iron Absorption (Heme vs. Nonheme):
- Heme iron accounts for ~10% of total iron intake, but is well absorbed (~25%).
- Nonheme iron accounts for ~90% of total iron intake, but is less well absorbed (~17%).
Iron Transport and Recycling:
- Transferrin transports iron in the blood.
- Liver/spleen break down old red blood cells.
- Iron is packaged into transferrin and stored in ferritin/hemosiderin.
- Bone marrow incorporates iron into hemoglobin in red blood cells.
Significant Sources: Red meats, fish, poultry, shellfish, eggs, legumes, dried fruits
Recommended Dietary Allowance (RDA):
- Men: 8 mg/day
- Women (19-50 years): 18 mg/day
- Women (51+ years): 8 mg/day
High Risk for Iron Deficiency: Women in reproductive years, pregnant women, infants, young children, teenagers

Zinc

Roles in the Body:
- Component of metalloenzymes
- DNA/RNA synthesis
- Hemoglobin synthesis
- Fatty acid metabolism
- Vitamin A release
- Carbohydrate metabolism
- Protein synthesis
- Blood clotting/wound healing
- Thyroid hormone function
- Behavior/learning performance
- Taste perception
- Sperm development
- Fetal development
Zinc Absorption:
- Rate depends on zinc status
- Phytates/fiber bind zinc, reducing absorption
Significant Sources: Protein-containing foods, red meats, shellfish, whole grains
RDA:
- Men: 11 mg/day
- Women: 8 mg/day
Deficiency Symptoms: Growth retardation, delayed sexual maturation, impaired immune function, hair loss, eye/skin lesions, loss of appetite
Toxicity Symptoms: Loss of appetite, impaired immunity, copper/iron deficiencies

Iodine

Roles in the Body: Component of thyroid hormones, regulates growth, development, and metabolic rate.
Iodine Deficiency:
- Simple goiter: Enlargement of the thyroid gland
- Goiter: Malfunction of the gland, iodine deficiency, or goitrogen overconsumption.
- Cretinism: Congenital disease, mental/physical retardation, caused by maternal iodine deficiency during pregnancy.
Iodine Toxicity: Symptoms include underactive thyroid gland and goiter.
RDA: 150 µg/day
Sources: Iodized salt, seafood, bread & dairy, plants grown in iodine-rich soils, animals that feed on those plants

Copper

Roles in the Body: Part of several enzymes, some are antioxidants
Deficiency Symptoms: Anemia, bone abnormalities, Menkes disease
Toxicity: Wilson's disease
RDA: 900 µg/day
Sources: Seafood, nuts, seeds, legumes, whole grains

Fluoride

Roles in the Body: Formation of teeth and bones, helps teeth resist decay
Deficiency: Tooth decay
Toxicity: Tooth damage (fluorosis)
AI:
- Men: 4 mg/day
- Women: 3 mg/day
Sources: Fluoridated water, seafood, tea

Chromium

Roles in the Body: Enhances insulin action (glucose tolerance factors)
AI:
- Men: 35 µg/day
- Women: 25 µg/day
Sources: Meat, liver, whole grains, brewer's yeast

Contaminant Minerals (Heavy Metals)

Contaminants: Mercury, lead, cadmium
Sources: Soil, water, air pollution
Effects: Disrupt bodily processes, impair nutrition
Lead Toxicity in Children:
- Learning disabilities, low IQ, behavior problems, slow growth, iron-deficiency anemia, dental caries, sleep disturbances, nervous system disorders, seizures, impaired hearing/coordination
Lead Toxicity in Adults: Hypertension, reproductive complications, kidney failure