Week 9: Trace Minerals

trace minerals

• dietary needs <20 mg/day

• best food sources = whole grains, legumes, dairy, meat, seafood

• bioavailability is a key consideration and varies across them

  • competition for absorption in GI tract

• frequent function: cofactors in enzymes

iron

avg. bioavailability ~15%; two versions:

1. heme

2. nonheme

roles and function of iron

1. component of blood (“heme” portion of hemoglobin → O2 transport)

   1. present in myoglobin (CO2 and O2 transport in muscles)

2. cofactor in energy metabolism

   1. cytochromes in mitochondria contain Fe (ATP production)

   2. conversion of substrates in TCA cycle

3. immune functions → production of lymphocytes and macrophages, cofactor in antioxidant systems

4. cofactor in NT synthesis in brain

fate of iron

body recycles and salvages Fe via liver and spleen (little excreted/shed…most common mechanism of Fe loss is from bleeding AKA blood loss)

heme iron, Fe⁺²

ferrous iron

• component of hemoglobin (RBCs) and myoglobin

• component of cytochromes in ETC

• found in animal-based foods (meat, poultry, fish)

• 2-3x more bioavailable than nonheme

nonheme iron, Fe⁺³

ferric iron

• found in plant foods

• form used in bread-product enrichment and fortification

• less bioavailable (bound form to oxalates/polyphenols in plant foods)

• absorption improves with vitamin C

Fe absorption

1. attaches to ferritin in enterocytes for temporary storage

2. hephaestin oxidizes ferrous to ferric iron 

3. transported in blood with transferrin

enhance Fe absorption

• sufficient HCL in stomach

• form (heme > nonheme)

• increased need for iron that occurs in blood loss, pregnancy, and growth

• vitamin C in SI at same time

• presence of MFP factor (meat, fish, poultry)

  • peptides in these foods help

decrease Fe absorption

• phytates in cereal grains (dietary fiber)

• oxalates

• polyphenols (tea or coffee)

• reduced HCl in stomach

• excess use of antacids

• excess minerals such as calcium, zinc, and magnesium

Fe RDA for adult F 19-50 yers

18 mg/day

dietary needs of Fe

• other adults RDA 8 mg/day, vegetarians have 2x higher need

• ~50% intake comes from enriched grain

• cooking in cast-iron skillet can increase nonheme

• intake patterns mapping NEEDS → Fe deficiency concern for premenopausal women

• males likely meeting daily needs

copper, Cu²⁺

two forms:

1. cupric (oxidized), Cu²⁺

2. cuprous (reduced), Cu⁺

enhance bioavailability of Cu²⁺

sulfur-containing amino acids

reduce bioavailability of Cu2+

• phytates in grains and legumes

• excess zinc: binds copper in enterocyte-based storage form

• competition with other like-valence minerals (iron, calcium, phosphorous)

functions of Cu²⁺

1. VITAL component of proteins needed for oxidation reactions

2. Cu²⁺-containing enzymes oxidize iron at enterocytes

3. part of cytochromes (protein that functions as an electron carrier) → essential for ATP production in ETC

4. contributes to connective tissue synthesis (collagen and elastin)

dietary needs for Cu

• DRI = AI: 900 micrograms/day

• food sources = organ meats, seafood, nuts and seeds, bran/whole grain

• some low-moderate sources eaten in abundance can cumulatively provide sufficient amounts

zinc, Zn⁺² function

1. growth and development (needed for DNA and RNA synthesis; regulates gene expression)

2. immune system functions and wound healing

   1. antioxidant and anti-inflammatory properties

   2. helps stabilize cell membranes (barrier to infection)

   3. component of enzymes and hormones in immune system

   4. may potentially reduce duration of cold symptoms

3. taste perception

zinc absorption

• regulated by small intestine → storage form increases to avoid toxicity: protein bound (metallothionine)

• high levels of nonheme iron, fiber, phyttes REDUCE absorption

• bound to undigestible substances and excreted in feces ← excess

dietary needs for zinc

RDAs: F 8 mg/day, M 1mg/day

selenium

1. important for enzymes regulating thyroid hormones

2. key component of group of enzymes called selenoproteins

selenoproteins

funcion as antioxidants, reduce free radical damage → decreased incidence of cancer

bioavailability of selenium

• higher than other trace minerals

• passive diffusion

• based on individual needs

• excess excreted in urine

selenium dietary needs

55 micrograms/day

• quantity in foods (nuts, seafood, dairy, meats, cereals and grains) dependent on soil

flouride

• not classified as essential; often added to water supply in 2/3 of US communities

1. beneficial impact on teeth

   1. forms crystalline fluoropatite in developing teeth, hardens tooth enamel by remineralizing it → resistant to decay

2. positive impact on bone health via increased osteoblast activity

• dietary sources = flouridated water (or bevs made with flouridated water)

iodine, I-

1. essential for thyroid function → used in making thyroid hormones T4 (thyroxine) 

2. food sources = seafood/seaweed; iodized salt

iodine deficiency

1. goiter: enlarged thyroid

2. cretinism/developmental delay if deficient during pregnancy

• mandatory iodization of salt reduced disease incidence → currently very low rates

iron deficiency

most common deficiency worldwide

• deficiency in childhood linked to worse cognitive development

• stores depleted and blood hemoglobin decrease

• RBCs contain less heme → small, pale presentation

• Sx = weakness, fatigue

copper deficiency

rare; can contribute to iron deficiency due to its role in oxidizing iron

zinc deficiency

• Sx = loss of appetite, changes in taste, impaired taste, hair loss, skin rashes

• chronic deficiencies in childhood → delayed sexual maturation, slow growth

selenium deficiency

• involved in Keshan disease (heart damage)

• potentially contributes to hashimoto’s disease (thyroid disorder)

trace mineral toxicity

• Sx = n/v/d

• excess levels lead to other mineral deficiencies

iron toxicity

potential with supplement consumption → causes constipation

iron poisoning

possible (in children) from accidental ingestion of supplements

• leading cause of poisoning death in children under 6 y/o

• 200 mg can be fetal → pills with >30 g are individually wrapped

iron overload

undetected excessive storage of iron over several years: results in tissue (heart, kidneys, liver, nerves) damage

• hemachromatosis: genetic disorder manifesting in adulthood results in this overload

excess copper intake

liver damage

• 2 genetic diseases can cause accumulation (menke’s and wilson’s disease)

selenosis

selenium toxicity

• Sx = brittle nails and hair, hair loss

• can cause GI symptoms, skin rash, damage to nervous system

fluorosis

condition of pitted teeth with white stains caused by too much fluoride (cosmetic)

• only impacts up to 8 y/o

• coach kids not to swallow fluoridated toothpaste

chromium

1. improves insulin effectiveness (impact on insulin production)

• very limited bioavailability: content in foods dependent on soil composition

• some research suggests positive impact on diabetes risk

molybdenum (Mo)

1. part of metalloenzymes

2. food sources - legumes, grains, and nuts

3. metalloenzyme component → amino acid metabolism, redox reactions, cofactor in enzyme reactions

metalloenzymes

important for amino acid metabolism, oxidation-reduction reactions; act as cofactor in enzyme reactions; metabolism of CHO, fats, and amino acids (ie; start of TCA cycle pyruvate → oxaloacetate)

manganese

1. cofactor for metalloenzymes (metabolism of CHO, fats, and amino acids)

   1. ie; start of TCA cycle: pyruvate → oxaloacetate)

2. food sources - plant foods (whole grains, nuts, legumes, veggies, fruits)

manganese toxicity

occurs from environmental contamination/pollutant exposure → causes nervous system damage