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
Zn food sources and absorption
Foods:
Widely distributed, but animal sources = richest; (beef > poultry > fish)
Plants: whole grains, legumes
Absorption:
Inhibited by phytate
Typically ~ 25-30%
Not increased by Zn deficiency
Can excrete Zn (in contrast to Fe), don’t really have stores
Breast milk Zn levels go down over time and are independent of maternal intake
Who is at risk for Zn deficiency
BF Infants (> ~ 6 mo) & young children – high growth rate, low intakes
Pregnant & lactating women
Elderly – low intake
Monotonous. plant based diets: increased phytate
GI illness/injury: increased endogenous losses
Wounds/burns healing: tissue repair
Zn Deficiency
Moderate-severe: Dermatitis (acro-orificial) Personality changes Immune dysfunction Delayed sexual maturation Anorexia Diarrhea Inherited defect in Zn absorption: Acrodermatitis Enteropathica (AE)
Severe Zn Def (Acquired AE):
Infants: diarrhea, growth failure, RASH
Rapid response to Zn supplementation
Mild Zn deficiency
Mild:
Growth delays
Anorexia
Impaired immune function
Mild Zn deficiency much more common than moderate-severe deficiency;
Globally, Zn deficiency 2nd only to Fe deficiency
Stunting is strongly assoc w/ Zn deficiency
Supplementation also decreased prevalence of diarrhea and pneumonia:
WHO: 20 mg/d Zn x 14 d for acute diarrhea (+ORS)
Zn deficiency in US
Older infants & toddlers, esp breastfed
Breast milk low in Zn after 6 mo
Diets low in meat
Presentation:
Growth faltering (weight & linear)
Poor appetite
Prompt response to supplementation; transition to dietary sources
Hospitalized pts: esp gi illness/diarrhea
Elderly – associated w/ ↑ incidence pneumonia
Zn toxicity w/ supplements
LOW – much less so compared to iron High doses (> 50 mg/d) leads to decreased Cu absorption (& neuropathy) High doses associated w/ decreased HDL-cholesterol
High dose Zn lozenges x few days for acute pharyngitis? (mechanism: suppresses viral replication?)
