week 8- micronutrients Flashcards
(48 cards)
• trace elements:
o essential: Cr, Co, Cu, I, F, Fe, Mn, Mo, Se, Zn
o NE: Ni, Si, Sn, V, B, Li
o Content in plant foods depends on soil content
o difficult to quantify biochemically
o Bioavailability influenced by other diet factors (esp other minerals)
• First basic law of nutrition:
o No nutrient is absorbed and utilized to the full extent that it is consumed
• Bioavailability
o May refer to either % nutrient ingested or % absorbed
o ingested preferred
o absorbed hard to determine, need indirect analysis; more accurate
o BA= a post-absorption assessment of % absorbed that becomes functional to the system
o Absorptive and assimilation phases
• Important for mineral absorption:
o Acidic pH of stomach: dissociation of minerals from food protein-bound state
o Pancreatic HCO3 neutralizes acidic chyme → form mineral complexes w organic acids & (-) charged amino acids (Ca aspartate, Mg oxalate)
o → ↑ absorption
• Slop ratio method:
o Asses bioavailability
o Ex: measure bodyweight of growing chicks
o ↓ BW will show when nutrients are ↓BA
o Steeper slop means more BA
• Balance approach:
o “keeping the status quo”
o Match input w excretion: balance, (+) growth, or (-) wasting
o Assess ability to: store, recover loss of turnover, delay appearance of clinical signs
o Problems: endpoint, time critical, can’t look at past exposure/adaptation
• Absorption/excretion vs retention
o Ex: 2-picolinic acid ↑ Zn absorption in rats by 60%
o But also ↑ excretion
o So no net effect on RETENTION
o hence no ↑ BA
• Why Not Absorption Alone as an index of Bioavailability?
o Assimilation major part of mineral’s BA, need assess separately
o Ex: only 0.5/5 mg X absorbed (10% absorption)
o → 0.21 mg absorbed becomes functional (42%)
o = only 4.2% of ingested is assimilated (vs 10%)
• Functional Response to Mineral Intake
o ↓Intake: Def state → interfere w enzyme activity & structural protein integrity
o ↑Intake: mb → toxicity; Any element mb harmful if body’s intake exceeds ability to use/store/excrete
o Optimal: Max fxn enzyme systems, structural proteins, etc; min toxicity potential
• Optimal Intake Approach for Assessing Requirement:
o Intake should: optimize physical/mental performance, tx dz, ↑longevity
o Problem: “should duplicate human milk”- too general, Defies population-based approaches
• Population/clinical approach:
o Link dz state & structural/fxn abn w known biochemical/fxn changes
o Parameters:
o Growth rate
o Physical appearance (skin, bone, hair, etc)
o Physiological impairments (GI, immune, nervous)
o Cognitive fxn
o Biochemical impairments (stress, enzymes, metabolic)
o Medical (prone to dz)
• Traditional Approaches to Determining Mineral Status:
o Body stores of mineral
o Overt response to ↑ mineral intake
o Phsy signs def: Stunted growth, Overt abn
o Internal signs def (biomarkers): Tissue/blood levels, Mineral binding proteins levels: Fxnal Assays, Enzyme assays
• Biomarkers; Ex: Body stores of a mineral:
o Ideal: reliable internal factor, responds directly, specifically, quantitatively to changes in a mineral’s homeostasis
o Applies mainly to Fe:
o Circulating ferritin = measure of Fe tissue stores
o Total iron binding capacity (TIBC)
o Transferrin saturation
o HCT, Hb, RBC morphology
• Blood/plasma mineral status assessment:
o Serum/plasma: “most popular” for element status, mb NOT accurately reflect whole body mineral status
o Whole blood: Best for STAT determinations of Na & K; mb for toxic metal poisoning
o RBCs & WBCs: Intracellular mineral content mb BEST correlation w nutritional status
• Urine, hair mineral stat assess:
o Urine: Excretory aspect of mineral balance, if renal fxn is adequate; daily dietary intake shold be constant to reflect nutritional adequacy
o Hair: Essential elements = controversial. Mb screen for heavy metals. ↑ metabolic activity and sulfhydryl group concentration concentrate heavy metals up 100x blood levels
• Functional indices:
o ↓ intake of some minerals → disrupt biochemistry: ↓enzymes, hormones, alt tissue morphology
o Important: direct connection bw mineral in question and fxnal component
o Ex: suspect I def → check T4
o Fe def → Hb
o Sel def → glutathione peroxidase
• Iron, from diet to blood:
o Fe2+ and Fe3+ insoluble, need special transporter
o Food Fe mostly Fe3+, tightly bound to organic molecules
o Stomach acid: Fe can dissociate
o → react w fructose, ascorbic acid, citric acid → soluble in intestine fluid
o DMT1 (divalent metal transporter 1): moves Fe across intestinal cells, store as ferritin (Fe3)
o Must reduce to Fe2 to release from ferritin
o → oxidized to Fe3 via ferroxidase ceruloplasmin → transferrin → body
• Iron in blood:
o Purpose: O2 transport by Hb
o Apoferritin assimilates up to 4,300 Fe to form Fe storage protein ferritin
o Ferritin → available storage form for Fe in RES
o Apotransferrin (apoTf): protein, can bind 2 Fe → transferrin, Fe carrier in plasma
• Daily Fe turnover:
o Absorb 1-2 mg
o → plasma transferrin, 4 mg → myoglobin (4 mg)
o → RBCs (BM, 20 mg), RBCs 2.5 g, RBCs (RES, 20 mg)
o Body stores: 1000g (M), 300-500g (F)
o → excrete (GI, stool) 1-2 mg
• IDA:
o Hypochromic microcytic; o Occasional Target cells o Pencil shaped poikilocytes o ↓ reticulocytes o Transferrin/TIBC: Normal to High o Serum ferritin: ↓ (Very low)
• Ferritin plasma, stores, problems:
o Most sensitive indicator of iron stores
o Adults: 1ug/L plasma = 8 mg stored Fe
o ↓ 12 ng/L = no Fe stores
o Kids: 1 ug/l = 14 mg stored
o Avg M: 112 ug, F: 36, Kids: 23
o Acute phase protein
o ↑ in: inflame, infx, dz (CA esp colon, CV), EtOH, hyperglycemia, obesity
• Transferrin saturation:
o TIBC (total iron binding capacity) o UIBC (unsaturated iron binding capacity) o 33% normal, 47% in AM (after fasting), 13% at night
Soluble transferrin receptor conc of plasma
o New concept, good index of early Fe def
o Basis: cells that need Fe express transferrin recpetors
o Extracellular domain of receptors released into plasma
o # receptors in plasma proportional to # expressed on cell surface
o = measure of Fe requirement
• Iodine:
o body normally has 20-30 mg, > 75% in thyroid
o rest in mammary gland, gastric mucosa, blood
o main known fxn: thyroid hormone
