Transcript Lecture 20: Trace Minerals

Trace Minerals
Lecture 18
Readings: Chapter 13: pages 429 – 453 (Omit
“Molybdenum”, “Other Trace Minerals” and
“Contaminant Minerals” on pages 450 and 451)
Next lectures: Highlights 10, 11, and 13
Overview
• trace minerals required only in miniscule amounts
• content contained in foods dependant on soil content,
water composition, and processing of foods
• interactions among trace minerals are common
• include:
– iron
– zinc
– iodine
– selenium
– copper
– fluoride
– chromium
Iron
• exists in two forms:
– “reduced” or ferrous iron (Fe2+)
– “oxidized” or ferric iron (Fe3+)
Functions
• forms part of electron carriers called ______________
in the electron transport chain
• forms part of proteins ________________ and
________________ enabling these proteins to accept,
carry and release oxygen
• required by enzymes that synthesize collagen,
hormones, neurotransmitters, and amino acids
Iron
Absorption and Metabolism
• iron is not readily excreted from the body
• iron balance is maintained by adjusting absorption
Types of Iron
a) _____
• from food derived from animal food sources
• 25% absorption
b) _________
• from both animal and plant derived foods
• only 10% is absorbed
Iron
Sources
Iron
Sources
Others
• broccoli, spinach, dried fruits, eggs, legumes, enriched
grains and cereals
Contamination Iron
• iron found in foods as the result of contamination by
inorganic iron salts form iron cookware or iron
containing soils
Recommendations
Men:
Women:
Iron
Factors Enhancing
Absorption
Factors Inhibiting
Absorption
Figure 13-1, page 431
Iron
Transport and Storage
• the intestine absorbs iron and stores it in protein called
– iron that is not needed is lost when intestinal cells
are shed
• when body needs iron, it is moved to another protein
called
• transferrin transports iron to the rest of the body where
it is needed
e.g. bone marrow where red blood cells are
synthesized
Figure 13-1, page 431
Iron
Transport and Storage
• surplus is stored in ___________ in the liver, bone
marrow and spleen
• even greater concentrations of iron lead to storage of
iron in another protein called ______________
• storage is important to:
Iron
Deficiency
• most common nutrient deficiency world wide
• prevalence is higher in less developed countries
• greatest risk for women in reproductive years, pregnant
women, infants and young children, and teenagers
Ways Iron is Lost from the Body…
• some iron is lost daily from the digestive tract
• only tiny amounts lost through feces, urine, sweat and
shedding skin
• lost with ___________
Iron
Deficiency cont.
Stages in the Development of Deficiency
1.
– measured by assessing serum ferritin
2.
– decreased serum iron
– levels of serum transferrin  to enhance absorption
3.
– insufficient iron to produce hemoglobin
– accumulation of erythrocyte protoporphyrin
– decrease in hematocrit
Iron
Deficiency cont.
Symptoms
a)
• red blood cells are small and pale
• results in fatigue, weakness, headaches, pallor, poor
resistance to cold
b)
• appear first
• unmotivated, apathetic, physically unfit
• “pica” = appetite for ice, clay, paste and non-food
substances
Iron
Toxicity
• extra dietary consumption generally poses no extra
risk because iron absorption decreases when body
needs decrease
• excess iron is referred to as “iron overload”
• hereditary disorder characterized by enhanced
iron absorption
• results from long-term overconsumption of iron
• characterized by deposits of hemosiderin in
tissues
Iron
Toxicity cont.
Symptoms & Consequences
• tissue damage, deposits of iron
• apathy, lethargy and fatigue
• increased risk of infections
• increased risk of heart disease:
– free iron acts as an oxidant
– may oxidize LDL and contribute to the development
of atherosclerosis
• increased risk of cancer
– increased free radical formation may contribute to
DNA damage
• poisoning in children if ingest supplements
Zinc
Functions
• acts as a cofactor for many enzymes
Example:
• assists in
• important for growth and development
– required for DNA and RNA synthesis
• synthesis of heme in hemoglobin
• releases Vitamin A from stores and converts to its
active form (retinal) in the retina
• forms part of an antioxidant enzyme that protects from
free radicals
Zinc
Functions cont.
• stabilizes cell membranes and helps protect them from
free radical attack
• interacts with platelets in blood clotting
• required for the synthesis, storage, and release of the
hormone insulin
• regulates thyroid hormone function
• influences behaviour and learning performance
• plays important role in protein synthesis
• participates in carbohydrate, fatty acids and alcohol
metabolism
• others: sperm production, fetal development, taste
Zinc
Absorption and Metabolism
• absorption rate varies between 15 - 40%
– dependant on zinc status
– absorption inhibited by fibers and phytates
• after absorption may be stored by the protein
• transported in the blood by two proteins:
– albumin
– transferrin
Zinc
Interactions
• an excess of dietary iron may reduce zinc absorption
– a dietary iron : zinc ratio > 2 : 1 decreases zinc
absorption
• large doses of zinc:
– inhibit iron absorption
– interferes with copper absorption
Zinc
Sources
• richest sources are protein rich foods
Examples
Recommendations
Men = 11 mg/day
Women = 8 mg/day
Zinc
Deficiency
• most vulnerable are pregnant women, young children,
the elderly, and the poor
Symptoms
• severe growth retardation and arrested sexual
development during growth
Zinc
Deficiency
Symptoms cont.
• diarrhea
• symptoms of a Vitamin A deficiency
• impaired thyroid function
• altered taste perception
• anorexia
• impaired glucose tolerance
• slowed wound healing
• impaired immune function
Zinc
Toxicity
• excessive doses may result in vomiting, diarrhea,
headaches
• may interfere with ______ and _________ absorption
and metabolism
Iodine
• iodine in foods is converted to its ionic form iodide by
the body
Functions
• an integral part of ________________
• thyroid hormone has many important functions
including:
– regulation of _______
– regulation of body temperature
– necessary for reproduction and growth
Iodine
Sources
• iodized salt, ocean fish, plants grown in iodine rich soil
• average intake of North Americans is above
recommendation but below toxic levels
Iodine
Deficiency
• results in hypothyroidism and causes an enlargement
of the thyroid gland called a ____________
• maternal iodine deficiency during pregnancy leads to
_____________ in the developing fetus
– affects 6 million people worldwide
– characterized by severe physical and mental
retardation
Iodine
Toxicity
• also enlarges the thyroid gland causing a __________
• poses risk of suffocation for a fetus is excess
consumed during pregnancy
– goiter may block airways
• upper limit is 1000 mg per day
Note
• a goiter may also develop from excess consumption of
___________, an anti-thyroid substance found in
plants of the cabbage family
Selenium
Functions
• forms part of the enzyme _______________________
– acts as an ___________
Deficiency
• associated with a predisposition to a type of heart
disease
– Keshan disease, also linked to a viral infection
• may be associated with an increased incidence of
some cancers
Toxicity
• high doses produce vomiting, diarrhea, hair loss, skin
lesions and neurological problems
Copper
Functions
• forms part of several enzymes including __________
______________
– an _________________
• important for the synthesis of ____________
Sources
• legumes, whole grains, nuts, shellfish, organ meats,
seeds, water
Copper
Deficiency
• rare, may be associated with excess Vitamin C which
interferes with absorption
• symptoms include _________________
• in animals leads to increased blood cholesterol and
damage to blood vessels
Toxicity
• rare
• may interfere with iron and zinc metabolism
Fluoride
Functions
• forms ____________________ in teeth
– replaces the hydroxyl (OH) in hydroxyapatite
crystals
Deficiency
• associated with _____________
• _______________________________ confers best
protection against dental caries
• primary source of fluoride is drinking water; also in tea
and seafood
Fluoride
Toxicity
• ____________
– damage to teeth that pits and stains the enamel
• also leads to nausea, vomiting, diarrhea, chest pain,
and itching
Chromium
Functions
• regulates carbohydrate and lipid metabolism
• enhances _______________
Sources
• present in a wide variety of foods
• rich sources include liver, brewer’s yeast, whole grains,
nuts and seeds
Deficiency
• produces a ____________________ marked by an
inability to use glucose normally