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

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:

Figure 13-1, page 431

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

IronToxicity 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 g 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