Micronutrients (review w/ handout) Flashcards
Trace minerals
Iron Copper Chromium Iodine Selenium Fluoride *Zinc Molybdenum Manganese
Definition: Mineral for which daily intake is
bioavailability
the extent to which other dietary constituents affect the absorption & retention of a nutrient;
Trace minerals especially susceptible to interference w/ absorption
Iron: total body iron and functions
Total body iron ~ 5 g
~ 50% as hemoglobin iron
Storage Fe: adults 300-1500 mg;
(Fe overload disorders: 40-50,000 mg)
Functions:
- O2 transport in blood & muscle (Hb & myoglobin)
- Electron transport (cytochromes)/respiratory chain
- Enzymes for activation of O2 (wbc, oxidases, oxygenases)
- Enzymes: dopamine synthesis, CNS myelination (
Food sources of iron
Heme:
Meats/flesh, liver (all milks = poor source)
Non-heme:
Plant sources: legumes, whole grains, nuts;
Fe-fortified foods (infant formula, cereals/grains)
Fe homeostasis: absorp/bioavail
Form: Heme Fe (better absorption)» non-heme
(>30% vs
Phytic Acid
-6 phosphate ring with negative charges
-Binds cations (Zn, Fe, Ca) in gut lumens; humans w/o phytases
-antioxidant in gut
(Most common feed enzyme: added to ~90% poultry & ~70% pig diets; decreased P pollution)
High in grains, legumes: Maize/wheat > legumes > rice
Globally, likely = major cause of dietary deficiencies
Oxidation state:
Fe3+ –> Fe2+ better absorbed;
ascorbic acid reduces Fe, forms complex
Host factors:
Deficiency leads to increased absorption
Inflammation leads to decreased absorption
Key factors: form of Fe & host status
Main point of regulation for Fe
absorption
Deficiency –> ↓ Hepcidin (liver)–> ↑ uptake
Inflammation –> ↑Hepcidin –> ↓ uptake
Once absorbed beyond GI tract, very efficiently retained/recycled
Loss (excretion): bleeding, cell sloughing
Stores: ferritin - liver, bone marrow, spleen
Transferrin: transports Fe in body; ~ no “free Fe”
At risk populations for Fe deficiency
BF Infants (> 6 mo ) - low stores /increased requirement
Premature/SGA infants
Young children - poor intake / ~increased requirement
Adolescent girls/young women – menstrual loss
Pregnant women - increased requirement
Blood loss (e.g. chronic infestations)
Obese (inflammation) & s/p bariatric surgery
Iron needs in infancy
At birth, use Fe in rbc’s; minimal dietary requirement; after ~ 4-6 mo, need to start making own rbc/Hb –> ↑ requirement
iron deficiency very common in older infants and toddlers
Iron deficiency etiology
Most common micronutrient deficiency in world, including U.S.
Poor bioavailability dietary Fe – plant/cereal staples
Dietary inadequacy – e.g. excessive milk intake
High demand
Hemolysis: increased losses / inc rbc production (e.g. helminths)
Pregnancy & infancy: inc rbc production & growth, low stores at birth (“early” cord clamping)
Chronic immuno-stimulation (iincreased hepcidin)
effects of iron deficiency
Iron deficiency anemia: decreased work capacity/exercise tolerance
Fatigue, listlessness, irritability, attention deficit, sleep disturbance (e.g. RLS)
Impaired growth
Anemia (microcytic, hypochromic)
Reduced O2 carrying capacity
Impaired cognitive function in developing brain
Irreversible, even w/ correction of deficiency/anemia
Iron toxicity
Potent pro-oxidant: avoid unnecessary supplementation (if replete, ↓ growth, ↑ oxidant stress, ↑ inflammatory markers, ↑ mortality; (-) effects on microbiome)
Normal individuals able to regulate absorption Hereditary hemochromatosis (=defect in hepcidin): absorption excessive --> accumulate Fe --> liver damage
Fe overdose = toxic
hemorrhagic gastroenteritis, shock, liver failure; ± fatal
Clinical Implications of Fe
Iron deficiency (w/o anemia) very common: Behavioral & learning/developmental effects Critical window of brain development
In setting of acute inflammation/illness…
Absorption will be poor due to hepcidin stimulation
In developing countries, chronic immuno-stimulation likely contributes to iron deficiency
Administering Fe = ineffective, pro-inflammatory
Zinc: total body and actions
Total body Zn: ~ 2 gram
Multiple, diverse functions
Regulation of gene expression (Zn fingers)
Stabilize molecular structures - subcellular constituents and membranes
Co-factor for hundreds of enzymes
Modulates activity of hormones & neurotransmitters
Nutritional/physiologic roles of Zn
Growth & cellular/tissue proliferation: Somatic/linear growth Immune system Wound healing GI tract integrity Skin
Antioxidant
Sexual maturation
