Zinc Flashcards
causes for Zn deficiency globally
nleavened bread (phytate)
hot climate: sweat losses of Zn little animal protein
mature males have higher requirement due to semen production
Functions: in > 300 enzymes
→ associate with DNA, RNA polymerases
absorption Zn
Like other divalent metals, absorption of zinc influenced by other dietary factors.
The storage protein Metallothionein (MT) is made when zinc absorption into the enterocyte increases.
MT binds Zn -> prevents excess Zn absorption (i.e. Zn likely won’t cross the BL membrane)
Zn absorption enhancers
organic acids
glutathione
amino acids
decrease pH
Zn inhibitors
phytic acid
oxalic acid
polyphenols
selected nutrients
increase pH
bound Zn in small intestine
bound Zn in food HCl, proteases, nuclease
uptake of Zn on BBM through
uptake through ZIP4
what happens in absorption when Zn is at high intakes
absorbed paracellularly
how is Zn stored in cells
as metallothionein
how does Zn travel out of cells
bound to proteins in blood albumin and alpha-2-macroglobulin
what does oxalic acid prefer to bind
Ca > Mg > Cd > Zn > Mn, Ni, Fe, Cu
phytate prefers to bind
Zn
functions of Zn list them
- metalloenzymes
- regulate gene expression
- hepatic synthesis of retinol binding protein
Zn role in metalloenzymes
a) structural stability
participate at regulatory site
* not redox active (stays in +2)
b) over 300 across all enzyme classes- many metabolic pathways
c) cytosolic superoxide dismutase (CuZnSOD)
conjugase (poly-glutamic folate - POLYGLUTAMATE HYDROLASE -> mono-glutamic folic acid
role of Zn in gene expression
Zn binds to specific transcription factors, which change their shape to look like a “finger”.
The “zinc finger” stabilizes the structure, which interacts with DNA.
e.g. permits hormone binding (T3, calcitriol,
retinoic acid) to DNA
Zn and vit A
hepatic (liver) synthesis of retinol binding protein - transport RBP and vit A bound
Zn EAR based on
functional analysis of Zn losses
RDA for Zn
M: 11mg
W: 8mg
food source of Zn
oysters
meat
pulses good but phytate binds Zn
F&V not a good source
Zn Deficiency assessment
Difficult to assess using plasma Zn because Zn redistributes
With infection, plasma Zn moves into liver as interleukin-1 induces metallothionein synthesis -> deprive bacteria of Zn for use
[infection affects nutrients – to make unavailable to pathogens]
signs of Zn deficiency
collagen defects, dermatitis = ↓ Zn-dependent enzyme in connective tissue
poor growth of children (↓ cell division) = stunting
night blindness (low retinol binding protein release from liver)
unique signs of Zn deficiency
- Hair zinc decreases
*proper procedures for collecting hair are required
*Difficult to interpret (e.g. varying hair growth) - Lose one’s taste (hypoguesia)
- Unexpected hair loss (alopecia)
- Slowed puberty in males (problem in some Middle Eastern countries in 1960s)
Population groups at risk in North America
Older adults
Vegetarians
Alcoholism
Limited income
Children and adolescents
More likely “marginal” Zn status – assessment difficult
Pregnant and lactating women
Needs increased by trauma, malabsorption or diarrhea
UL for Zn
40mg food and supplements
in excess: increased synthesis of metallothionein to hold Zn storage
UL based on concern that excess Zn could cause Cu deficiency (CuZn SOD)
with excess ZN more MT made to bind ZN but MT binds other metal divalent cations, especially Cu
