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Flashcards in Micronutrients and Trace Elements Deck (21)
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1

Iron: physiologic functions

  • Oxygen transport in blood (hemoglobin) and muscle (myoglobin)
  • Electron transfer enzymes (cytochromes)
  • Enzymes for activation of oxygen (oxidases and oxygenases)
  • Enzymes for DA synthesis, myelination

2

Iron: dietary sources

  • Heme iron:
    • Cellular animal protein: meats, poultry, liver
    • Milk is poor source
  • Non-heme iron:
    • Legumes, nuts, whole grains (especially enriched/fortified), green leafy vegetables
  • Absorption of non-heme iron (< 10%) much lower compared to animal sources (> 40%)

3

Iron: chemical factors affecting bioavailability

  • Dietary factors that form insoluble complexes (phytate, tannins, phosphate, oxalate) decrease absorption
  • Factors affecting oxidation state (absorption enhanced for reduced state of iron - Fe2+ over Fe3+)
    • Vitamin C helps with absorption
  • Chemical form
    • Heme iron enhances absorption of non-heme iron
  • Mineral-mineral interactions: excessive Zn or Cu decrease Fe absorption

4

Iron: host factors affecting bioavailability

  • Physiologic states
    • Pregnancy, growth, erythropoeisis increase absorption
  • Iron deficiency increases absorption
  • Inflammation --> increased hepcidin from liver --> decreased absorption at enterocyte
  • Quantity present in meal/gut lumen (inverse relationship)

5

Iron: key aspects of homeostasis

  • Intestinal absorption is main point of regulation
    • Once in, hard to get out in conditions of excess
  • Efficiently and effectively retained
    • e.g. recycling from RBC/Hb breakdown
  • Bleeding: major route of iron loss
  • Stores: liver, bone marrow, spleen

6

Iron: etiology of deficiency

  • Bleeding and cell sloughing --> iron deficiency
  • No major regulated way to get rid of excess iron

7

Iron: populations at risk for deficiency

  • Infants > 6 mo old, premature infants, toddlers: low stores, high requirement
  • Adolescents: relatively high requirement + poor intake
  • Pregnant women: increased requirement
  • Populations with chronic infestations (helminths, etc. causing intestinal blood loss)
  • Bariatric surgery patients
  • Hospitalized elderly or elderly in long-term care facilities
  • Menstrual loss
  • Sports anemia

8

Iron: manifestations of deficiency

  • Anemia (microcytic, hypochromic)
  • Decreased exercise/work tolerance
  • Fatigue
  • Listlessness
  • Impaired cognitive function
  • Restless leg syndrome
  • Impaired growth

9

Iron: treatment of deficiency

  • Oral iron supplements (ferrous sulfate)
  • 30-60mg/day for 2-6 months
  • Replenishment of iron stores
  • For infants/children: 2-6 mg/kg/day

10

Iron: prevalence of deficiency

  • Most common nutritional deficiency in world, including USA

11

Iron: toxicity potential

  • Iron is potent pro-oxidant - avoid unnecessary supplementation
  • Caution with IV iron and frequent blood transfusions (iron overload)
  • Hemosiderin production generates excess iron
  • Large supplementation can interfere with absorption of Zn, Cu, and other minerals
  • Fe2+ overdose = hemorrhagic gastroenteritis, liver failure, shock
  • In children: 1-2g can be fatal

12

Zinc: physiologic functions

  • Growth and tissue proliferation
  • Sexual maturation
  • Taste
  • Immune function
  • Wound healing
  • Regulation of gene expression via zinc finger transcription proteins --> both DNA and RNA metabolism
  • Structural roles in membrane stability
  • Metalloenzymes (> 200!)

13

Zinc: dietary sources

  • Widely distributed animal products --> oysters extremely high
  • Beef > poultry > fish, milk, eggs
  • Relatively high in whole grains, legumes, seeds
  • Lower absorption from plant foods

14

Zinc: factors affecting bioavailability

  • Absorption impaired by phytate (high in corn, legumes, nuts)
  • Absorption NOT increased with deficiency (unlike iron)

15

Zinc: key aspects of homeostasis

  • Intestinal absorption and excretion of dietary zinc through intestine are important for body pool
  • Zinc secreted into GI tract with biliary secretions, some reabsorption --> route for excessive loss

16

Zinc: populations at risk for deficiency

  • Low birthweight infants and youth: high growth rate and marginal intake
  • Breastfed infants: human milk low in Zn
  • Pregnant/lactating women: high demand for embryogenesis
  • People on monotonous, plant-based diets (especially high in phytate)
  • Bariatric surgery patients: up to 40% due to decreased protein intake
  • Elderly: poor Zn intake associated with increased pneumonia incidence
    • Cu/Zn ratio in elderly associated with higher mortality and may be biomarker of aging

17

Zinc: consequences of mild deficiency

  • Growth delays/stunting
  • Anorexia
  • Impaired immune function
  • Impaired neurocognitive development
  • Much more common worldwide

18

Zinc: consequences of moderate to severe deficiency

  • Characteristic dermatitis (acro-orificial)
  • Diarrhea
  • Immune dysfunction
  • Delayed wound healing
  • Taste impairment
  • Anorexia
  • Personality changes

19

Zinc deficiency: acrodermatitis enteropathica

  • Inherited defect in enterocyte Zn transporter
  • Fatal condition if not treated
  • Responds to high doses of Zn supplements (lifetime)
  • Presents with severe dermatitis, growth failure, diarrhea

20

Zinc: prevalence of deficiency

  • Worldwide, likely to be widespread
  • Estimated to account for 0.4 million deaths/year in children < 5 years of age
  • 2nd only to vitamin A deficiency (estimated to be responsible for 0.6 million deaths/year)
  • One of the cheapest and most beneficial public health efforts is zinc supplementation

21

Zinc: toxicity potential

  • Relatively low
  • > 50 mg/day can decrease HDL cholesterol
  • Impair absorption of iron and copper
  • Cause nausea
  • Diarrhea