Transcript 0495116572_102931

Chapter 13
Ultratrace Elements
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Introduction
• Definition
– Estimated, established or suspected
requirements of <1 mg/day
– Some of these were covered in
Chapter 12 because an RDA/AI has
been set
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Arsenic
• Sources
– Content depends on soil & pollution
– Foods of marine origin
– Most toxic: inorganic arsenite,
trivalent organoarsenicals
– Less toxic: pentavalent, methylated
arsenic compounds
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Arsenic
• Absorption
– Simple diffusion
• Transport
• Metabolism
– Organic - little or none in liver
– Inorganic - reduced, methylated or
both in liver
– Concentrates in skin, hair, nails
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Arsenic
• Functions
– Formation & utilization of methyl
groups generated in methionine
metabolism to S-adenosylmethionine
• Deficiency
– Impairs methionine metabolism
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Arsenic
• Excretion
– Mostly via kidneys in urine
• Recommended intake
– Suggested: 12-25 µg
• Toxicity
– Fatal at intakes of 70-300 mg
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Arsenic
• Assessment of nutriture
– Hair analysis
– Atomic absorption spectrometry
preferred
– Other methods:
• Mass spectrometry
• Neutron activation analysis
• Emission spectroscopy
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Boron
• Sources
– Fruits, vegetables, nuts, legumes
• Especially avocado, peanuts, peanut
butter, pecans, raisins, grapes
– Wine, cider, beer
• Absorption
– Passive diffusion
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Boron
• Transport
– In blood as boric acid, orthoboric
acid, borate monovalent anion
B(OH)4– Boron transporter
• Storage
– Bones, teeth, nails, hair
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Boron
• Excretion
– Mostly urine, also feces, sweat
• Functions
– Embryogenesis
– Bone development
– Cell membrane function & stability
– Metabolic regulation
– Immune response
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Boron
• Deficiency
– Studied in animals
– Symptoms related to suspected
functions
• Recommended intake
– Not established
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Boron
• Toxicity
– UL = 20 mg
• Assessment of nutriture
– Inductively coupled plasma emission
spectrometry
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Nickel
• Sources
– Nuts, legumes, grains, chocolate
• Absorption
– Carrier & passive diffusion
• Transport
– In blood: binds mainly to albumin,
also amino acids, other proteins
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Nickel
• Storage
– Throughout body in low
concentrations
– Highest in thyroid, adrenal glands,
hair, bone
• Functions
– Undefined
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Nickel
• Deficiency
– Animals: depressed growth, altered
mineral distribution, blood glucose
changes, impaired hematopoiesis
• Interactions with other nutrients
– Competes with other metal ions for
ligand sites
• Iron, copper, zinc
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Nickel
• Excretion
– Mostly urine, also sweat, bile
• Recommended intake
– Suggested: <100 µg/day
• Toxicity
– UL = 1.0 mg soluble Ni salts
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Nickel
• Assessment of nutriture
– Flameless atomic absorption
spectrophotometry
– No valid method for assessing human
status available
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Silicon
• Sources
– Plants contain more than animals
• Absorption
– Not well understood
• Transport
– Bound
– Free - orthosilicic acid, Si(OH)4
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Silicon
• Storage
– Concentrates in connective tissues
• Excretion
– Mostly in urine
• Functions
– Metabolic & structural role
– Bone, connective tissue & cartilage
formation, growth & development
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Silicon
• Deficiency
– Smaller, less flexible long bones &
skull deformation
• Recommended intake
– Suggestions range from ~5-35
mg/day
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Silicon
• Toxicity
– Suggested maximum: 1,750 mg/day
– Kidney stones
• Assessment of nutriture
– Serum/plasma
– Mass spectrometry, emission
spectroscopy, atomic absorption
spectrophotometry (preferred), etc.
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Vanadium
• Sources
– Black pepper, parsley, dill seed,
canned apple juice, fish sticks,
mushrooms
• Absorption
– Varies with oxidation states
– Vanadate mimics phosphate & uses
its transport system
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Vanadium
• Transport
– Converted to vanadyl in fluids
– Vanadyl binds to albumin & ironcontaining proteins
– Enters cells as vanadate using
phosphate transport systems
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Vanadium
• Storage
– Concentrates in bones, teeth, lungs,
thyroid gland
• Functions
– Many pharmacological effects
– No specific biochemical function
identified
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Vanadium
– Pharmacological effects:
• Inhibits Na+/K+-ATPase
• Stimulates adenylate cyclase
• These together affect transport of amino
acids across the intestinal mucosa
• Mimics the action of insulin (as vanadate
& vanadyl)
– Can substitute for zinc, copper, iron in
metalloenzyme activity
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Vanadium
• Excretion
– Mostly urine, also bile
• Recommended intake
– Suggested: 10 µg/day
• Toxicity
– UL = 1.8 mg/day elemental vanadium
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Vanadium
• Assessment of nutriture
– Neutron activation analysis
– Flameless atomic absorption
spectrophotometry (preferred)
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Cobalt
• Part of vitamin B12
• Can substitute for other metals in
metalloenzymes in vitro
– In vivo? No evidence of this
• Little evidence that ionic cobalt is
essential in humans
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