Transcript Micro nutrient notes

Micronutrients in normal human
growth and development
Dr. Mary Rose Sweeney
[email protected]
Micronutrients include
• Vitamins
• Minerals
• Trace Elements
Introduction to vitamins
• Vitamins are a diverse array of chemicals. They are required in very
small quantities, usually only a few micrograms or milligrams per day.
• They are essential for many of the processes carried out in the body.
• Most vitamins cannot be made de novo by the body, so a dietary intake
is essential to prevent deficiencies.
• There are a number of exceptions, Vitamin D can be synthesised by the
action of sunlight on skin, vitamin K, which can be synthesised by
intestinal bacteria and niacin which can be made from the amino acid
tryptophan. Synthesis of this type is often not sufficient to maintain
bodily functions so additional dietary intake is usually needed.
• Most vitamins were first identified in relation to their roles
in the prevention of specific deficiencies.
• Nowadays overt vitamin clinical deficiencies are rare in
western society (in the absence of illness causing the
deficiency e.g. cancer or malabsorption disorders).
• The focus is now placed on “optimal vitamin status”
because of the putative (reported) health benefits of same,
e.g. prevention of cancer, heart disease.
Classifications
• Vitamins are not chemically related.
• Classification according to principal roles has been
traditionally used to classify them e.g.
• antioxidant roles - vitamin C & vitamin E
• Maturation of bone marrow - folic acid & B12
• involvement in energy production pathways - B complex
• Other classification relate to solubility in
lipids A, D, E, K or water B & C.
• This is most commonly used.
Fat Soluble Vitamins
Vitamin A (Retinol)
• Vitamin A is the parent of a class of chemicals called
retinols (both natural and synthetic), which have many of
the structural features of vitamin A. Also included in the A
family are the provitamin A carotenoids, chief of which is
β-carotene. Many of these carotenoids are not converted to
vitamin A and are absorbed from the intestine unchanged.
Common examples include lycopene and lutein. Most
carotenoids act as anti-oxidants and epidemiological
evidence has shown that high intakes of carotenoids is
associated with a low incidence of CHD and cancer.
Preformed vitamin A does not have anti-oxidant properties.
Functions of Vitamin A
• Vitamin A is required for the normal growth
differentiation and development of tissues.
The effects of deficiency tend to be most
apparent in rapidly dividing cells such as
those of the skin and cornea of the eye.
• Vitamin A is necessary for the manufacture
of rhodopsin in the retina, necessary for
adaptation of vision in the dark.
Vitamin A Requirement
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Reference Nutrient Intake
children aged 1-10 yrs is 400-500µg/day
children aged 11-14yrs is 600µg/day
adults 650µg/day
pregnancy + 100µg/day
lactation + 350µg/day
Sources of Vitamin A
• Most preformed in the diet is from
• meat & meat products (61%)
• milk & dairy products (14%)
• fat spreads (13%)
Sources of beta-carotene
• Most concentrated dietary forms are
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carrots
red peppers
spinach
brocolli
tomatoes
Vitamin A Deficiency
• Low vitamin A status can result from any
condition which results in a significant fat
malabsorption.
• Symptoms can include
• impaired night vision
• loss of integrity of skin and mucous
membranes
• consequent increased risk of infection
Toxicity of Vitamin A
• Surplus amounts of vitamin A are stored in the
body in excessive amounts can cause liver damage
and can be fatal.
• High intakes of vitamin A are also potentially
teratogenic hence concentrated forms such as liver
should be avoided in pregnancy.
• Recommended maximum intakes are 9000µg/day
for men and 7500µg/day for women.
Vitamin D (calciferols)
• There are several compounds with vitamin D activity. Dietary forms
are principally cholecalciferol (vitamin D3) and ergocalciferol (vitamin
D2).
• Most of the vitamin D required by humans is produced by ultraviolet
light acting on the steroid 7-dehydrocholesterol, an intermediate in the
synthesis of cholesterol that accumulates in the skin but not other
tissues.
• However dietary intake is essential when
• 1) there is little or no exposure to UV light (Muslim women)
• 2) conversion is reduced (older people, or individuals with dark skin
(high melanin levels)
• 3) physiological requirements are particularly high, such as in young
children or during pregnancy.
Functions of vitamin D
• The active form 1,25-dihydroxyvitamin D is
involved in calcium homeostasis, mainly by
controlling the amount of calcium absorbed
and excreted.
• It also has a direct effect on bone synthesis
Vitamin D Requirement
• Reference Nutrient Intakes
• Infants under 6 months 8.5µg/day
• infants from 6 months up to 4 years 7.0µg/day
• 4-64 years, no specific recommendations, assumed
to get enough from sunlight in summer months
provided their skin is exposed
• Specific recommendation relate to Asian women,
pregnancy and lactation
Sources of Vitamin D
• Most dietary vitamin D comes from
• margarine and fat spreads 30%
• cereal products 24%
• oily fish 21%
Vitamin D Deficiency
• Risk of deficiency low provided people are
exposed to sunlight.
• May be high in institutionalised or housebound,
e.g. elderly or handicapped, or Asian women.
• Prolonged deficiency in children results in rickets
and in adults osteomalacia (bone tenderness, pain
and weakness)
• May also play a role in osteoporosis
Osteoporosis
• This is defined as a condition in which the amount of bone per unit
volume is decreased but the composition remains unchanged. The bone
becomes porous, due to the imbalanced action of the forming and
reabsorbing cells. Osteoporosis predisposes to fractures, particularly
the forearm and neck of femur. The latter leads to immediate
immobility and is associated with increased mortality and morbidity.
Nutrition status particularly calcium levels is thought to play a role in
its development. In addition other risk factors include, early
menapause, positive family history, being underweight, high alcohol
intake, and smoking. Women have a higher risk than men because they
have a lower peak bone mass and then have an accelerated loss of bone
in the menopausal years. Thus bone density falls below the so-called
fracture threshold many years earlier in women than in men.
Vitamin E (tocopherols)
• Vitamin E is an important anti-oxidant, and
because it is fat soluble, plays a major role
in preventing oxidative damage to lipidcontaining structures such as cell
membranes.
Vitamin E Requirement
• The biological function of vitamin E is general rather than
specific and hence the assessment of requirement is
difficult. Hence the COMA report 1991 did not set RNI but
instead set a safe intake level, considered adequate to
prevent deficiency
• > 4mg/day in men
• > 3mg/day in women
Dietary Sources of Vitamin E
• Most comes from fats either directly from
spreads and margarines (20%) or indirectly
from foods fried in spreads.
• Cereal grains also are a rich source
• Meat, fish, eggs provide about 20% also.
• Sunflower oil, wheatgerm oil are rich
sources. Olive oil is not a particularly rich
source.
Vitamin E deficiency
• Clinical deficiency is very rare and has only been
reported clearly in premature infants.
• However there is speculation that sub-optimal
deficiency at a population level may increase the
risk of some chronic diseases in which tissue
oxidation is involved, e.g. CHD, cataracts of the
eye.
• Groups at risk include: premature infants, medical
conditions resulting in fat malabsorption such as
cystic fibrosis
Toxicity of Vitamin E
• No adverse effects have been reported in
studies looking at intakes as high as
3200mg/day, hence safe upper limits have
not been yet been set.
Vitamin K
• Vitamin K activity is shown both by plant
(phylloquinone) and by the related
menaquinones which are synthesised by
intestinal bacteria.
Fuctions
• Known as the dietary derived coagulation
factor. It is thought to play a role in the
hepatic synthesis of the four pro-coagulant
factors II (prothrombin), VII, IX and X.
• In addition vitamin K is needed for the
gamma-carboxylation of at least two
coagulation inhibitors as well as several
proteins of unknown function
Vitamin K Requirement
• Few satisfactory studies have been carried out because of
the difficulty in inducing exclusive vitamin K deficiency.
• Requirement is based on maintenance of plasma
concentrations of vitamin K-dependent coagulation factors.
• Approximately 0.5-1.0 µg/Kg/day in adults
• Approximately 2.0 µg/Kg/day in infants due to reliance on
dietary intake alone (absence of menaquinones in early
life)
Dietary Sources of Vitamin K
• Vitamin K occurs in plants in the quinone
form and is particularly abundant in green
leafy vegetables, such as broccoli, spinach,
parsley, cabbage. The greener the leaves the
higher the content of vitamin K.
• Cows milk and human milk also supply a
source of vitamin K.
Vitamin K Deficiency
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In its severest form, vitamin K deficiency results in a bleeding syndrome due
to the lowering of circulating levels of the pro-coagulant factors and their
replacement by under carboxylated species.
Overt deficiency is almost never seen after the first few months of life, except
as a consequence of underlying disease affecting absorption or utilisation of
the vitamin. In contrast, infants are born with hepatic reserves of
phylloquinone but no menaquinones. This reserve builds up over several
weeks as a result of dietary intake. Spontaneous haemorrrhage can occur in the
newborn which is usefully fatal.Occurs in approximately 1.6/100,000 births.
Prophylactic vitamin K injection is given (1mg) at birth in the UK and Ireland.
Reports of increased incedence of childhood cancers as a result of this
treatment have ceased the administration of this in the US. Oral administration
is given instead.
It is not known why deficiency occurs in some infants. May be related to poor
maternal diet.
Vitamin K Toxicity
• Natural K vitamins seem remarkably free
from toxic effects when taken even in mg
doses.
• Synthetic preparations of menadione are
best avoided for nutritional purposes,
because they have been linked to
haemolysis and liver damage in the
newborn.
Water Soluble Vitamins
The B vitamins:Thiamin (B1)
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FUNCTIONS: Thiamin is required mainly during the metabolism of
carbohydrates, fat and alcohol. Diets high in carbohydrates require more of the
vitamin than diets high in fat.
REQUIREMENT: Epidemiological evidence suggests that beri-beri occurs
when intakes are 0.2mg/1000kcal or less. Hence requirements have been set at
0.4mg/1000kcal to allow for dietary variance.
SOURCES:All natural foods, however most important sources are plant seeds,
e.g. unrefined cereal grains, organ meats, pork flesh, nuts and legumes.
DEFICIENCY: Results from inadequate intake, poor absorption or increased
metabolic demand. Often seen in Asian countries caused by malnutrition, in
alcoholics and in conditions affecting intestinal absorption. Clinical deficiency
resuts in a condition called beri-beri. Can be dry or wet beri-beri. Dry is
characterised by progressive dyspnoea, odema and progressive weakness. Wet
is characterised by extreme muscle weakness and progressive polyneuropathy.
TOXICITY: No known toxicity identified.
Riboflavin (B2)
• FUNCTIONS: Riboflavin plays an essential role in all of the oxidative
processes on which man and other organisms depend.
• REQUIREMENT: There is a limited storage capacity for riboflavin
hence the margin between dietary intake resulting in deficiency &
tissue saturation is very small. Therefore dietary intake
recommendations are set at 0.6mg/1000kal with a minimum of
1.2mg/day for adults and 0.2mg/day in infants.
• SOURCES: Principal source is dairy products, poultry, meat, fish,
broccoli and spinach.
• DEFICIENCY: The principal signs of deficiency are a rash around the
nose, angular stomatitis and intense glossitis. Anorexia, intestinal
malabsorption and chronic alcoholism all precipitate deficiency.
• TOXICITY: No evidence ot toxicity at doses > than the RNI
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Niacin & Tryptophan
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FUNCTION: The generic descriptor “niacin” includes nicotinic acid and
nicotinamide, which functions as the reactive part of the nucleotide coenzymes
NAD (nicotinamide-adenine dinucleotide) and NADP (nicotinamide-adenine
dinucleotide phosphate) (which have major roles in oxidation & redution
reactions). Nicotinamide can be synthesised from the amino acid tryptophan.
Niacin, then is important in intermediary metabolism and requirement is
related to energy expenditure.
REQUIREMENT: There is no total satisfactory laboratory assessment of
niacin status. The mean observed requirement of niacin to prevent clinical
deficiency is 5.5mg/1000kcal. Hence RNI in adults is set at 6.6mg/1000kcal
and infants is 3.3-3.85mg/1000kcal.
SOURCES: Meat, dairy products, cereals such as oat bran
DEFICIENCY: pellagra which manifests itself as dermatitis, glossitis and
diarrhoea, with end-stage dementia. Occurs mainly in India and Africa.
TOXICITY: Large therapeutic doses have been shown to stimulate gastric acid
secretion with increased risk of peptic ulcers.
Vitamin B6 (Pyridoxine)
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FUNCTION: Vitamin B6 covers the group of metabolically inter-changable
compounds pyridoxal, pyridoxine and pyridoxamine, all of which can be
converted to the coenzyme pyridoxal-5-phosphate, which is essential for
protein metabolism and is involved in glycogen and lipid metabolism also.
REQUIREMENT: are related to protein intake, at 15mcg/g of dietary protein,
the following RNI are derived: Children: 0.7-1.0mg/day, adult men:
1.4mg/day, adult women: 1.2mg/day.
SOURCE: Cereal grains 20%, meat and meat products 20%, beverages (beer)
20%, potatoes 15%, milk products 12%.
DEFICIENCY: Rare but has been associated with metabolic abnormalities in
infants maintained on inappropriate synthetic diets and in severe alcoholics.
TOXICITY: Supplements are commonly taken by women suffering from premenstral syndrome, although the benefits remain sketchy. Teratogenic defects
have been reported at intakes of 50mg.
Vitamin B12 (cobalamin)
• FUNCTION: Vitamin B12 is required for the production of folate
coenzymes and in the synthesis of methionine from homocysteine. B12
is also needed for myelination of the spinal cord and maturation of red
blood cells
• REQUIREMENT: 80% of storage is in the liver and body turnover is
slow. The RNI for children is 0.5-1.0µg/day. Adults should consume
1.5 µg/day
• SOURCES: Only found in animal sources e.g. meat especially liver,
milk, eggs, fish, therefore vegans are at risk of deficiency.
• DEFICIENCY: megaloblastosis can occur. pernicious anaemia is an
auto-immune disease with diminished production of intrinsic factor by
the parietal cells of the stomach - B12 cannot be absorbed, end-stage is
a fatal irreversible neuropathy.
• TOXICITY: No toxic effects noted.
Pantothenic Acid
• FUNCTION: Is the precursor to coenzyme A which is
involved in energy metabolism.
• REQUIREMENT: approximately 3-7mg/day
• SOURCES: Widely distributed in plant and animal foods.
Rich sources include meats, fish, offal
• DEFICIENCY: No specific syndrome identified,
• TOXICITY:large supplemental forms may cause diarrhoea.
Biotin
• FUNCTION: Biotin is a cofactor for several enzyme
systems involved in the synthesis of fatty acids and in
gluconeogenesis.
• REQUIREMENT: Intake of 10-200µg/day considered adequate
and safe.
• SOURCES: Liver and Kidneys, yeast, nuts, plses, wholegrain cereals,
eggs
• DEFICIENCY: Unlike most other water-soluble vitamins biotin is
stored in the liver and hence deficiency is unlikely to occur
• TOXICITY:
Folate
• FUNCTION: Folate is essential for many of the methylation reactions
involved in the synthesis of RNA & DNA, and hence cell division.
• REQUIREMENT: RNI for children is 70-150µg/day, adults 200µg/day
and 400µg/day pre and during the first 20 weeks of pregnancy for the
prevention of Neural Tube Defects (NTDs).
• SOURCES: Very widely distributed in foods. Found in almost all
foods except fruit pastilles. Rich sources include liver, yeast, oranges,
green leafy vegetables. Nowadays fortified cereals, milk (supermilk)
and breads supply large additional sources.
• DEFICIENCY: results in megaloblastic anaemia . Sub-optimal levels
also associated with alzymers, CHD & stroke, colonic cancer.
Deficiency in pregnancy shown to cause NTDs.
• TOXICITY: May mask early symptoms of pernicious anaemia, may be
a risk for certain cancers e.g. childhood leukaemia
Vitamin C (ascorbic acid)
• FUNCTIONS: Vitamin C is a powerful reducing agent and electron
donor and affects many oxidation/reduction reactions. It has
antioxidant role in the aqueous component of tissues often in
conjunction with vitamin E which has an anti-oxidant role in lipid
structures. It also plays a role in the absorption of iron. It is also
thought to be important in wound healing.
• REQUIREMENT: RNI for children is 30mg/day. Adults 40mg/day.
Smokers have an increased turnover of vitamin C, hence RNI is set at
80 mg/day.
• SOURCES: Rich sources are citrus fruits, new potatoes, currants,
• DEFICIENCY: Scurvy
• TOXICITY: Intakes > 1g/day not recommended result in diarrhoea and
red cell lysis.
Minerals & Trace Elements
• Minerals and trace elements are, like vitamins, only required in small
or even trace quantities but are nonetheless essential for normal body
functions and growth and development. Those required in milligrams
tend to be referred to as minerals and those required in micrograms are
referred to as trace elements. They have a variety of roles are may be
necessary for
• Tissue structure - calcium, phosphorus important in bone structure
• Fluid balance - sodium, potassium in extracellular & intracellular fluid
• Cellular function - some are involved in intracellular transport
mechanisms
• Enzyme systems - many are required as coenzymes, cofactors in
metabolic pathways
• Neurotransmission - some influence electrical activity and are essential
in nerve function
Difficulties in Estimating
Requirement
• Their content in food can very according to
factors such as the soil in which plants are
grown, animal feeds, the species, ripeness
of plants or age of animal, and food
processes undergone.
• For this reason there is variability in DRVs
between different expert groups and
international bodies
Calcium
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Functions: The body requires considerable quantities of calcium in order to create and
maintain its skeletal structures. 99% of body calcium is deposited as calcium salts,
within the matrix of bones and teeth providing structural rigidity.The remaining 1% is
found between tissues and body fluids, where it plays many roles including involvement
in nerve transmission, muscle contraction and blood clotting.
Requirement: Requirements depend on the rate at which calcium is incorporated into
bone. Therefore high periods of growth such as infancy and adolescence require larger
amounts. Peak bone mass is achieved around 25 years of age so requirements fall after
this. 1-3 yrs: 350mg/day, 4-6yrs: 450mg/day, 7-10yrs: 550mg/day, 11-18 yrs,
1000mg/day for males,800mg/day for females, adults 700mg/day
Sources: milk, dairy products: cheese, yoghurt, canned fish: sardines, pulses
Deficiency: Lack of calcium can result in stunted growth and failure to achieve peak
bone density in early adulthood, hence increasing risk of osteoporosis in later life.
Failure to absorb calcium as a secondary conequence of vitamin deficiency results in
rickets in children and osteomalacia in adults as well as osteoporosis.
Toxicity: supplemental intakes of calcium even up to 2g/day have not resulted in any
toxic effects.
Phosphorus
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Functions: Is closely linked to calcium and protein metabolism.The majority
of the body’s phosphorus in stored in bone. About 15% also constitutes nucleic
acids (in DNA) and phospholipids. It is also involved in acid-base regulation.
Requirement:Requirements for phosphorus parallel calcium requirements. RNI
are therefore the same as calcium expressed in millimoles.
Sources: milk & milk products are the most concentrated forms, although
meat, fish, eggs, nuts, fruit, cereals and vegetables all provide moderate
amounts.
Deficiency: Unlikely to occur in a healthy individual. However phosphate
depletion can occur in blood and soft tissue in any disorder where pH is altered
e.g. excessive diarrhoea or polyuria. Symptoms include respiratory and cardiac
failure, neuropathy and tissue hypoxia.
Toxicity: large amounts are well tolerated by the body, however excesses of
70mg/kg body weight can cause hyperphosphataemia.
Magnesium
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Functions: Involved in many enzyme systems, such as those involved in
decarboxylation or phosphaate group transfer. It plays a vital role in skeletal
development, protein synthesis, muscle contraction and neurotransmission.
Metabolically, it also appears to be closely linked to calcium.
Requirement: Difficult to estimate. RNI for adult males is 300mg/day and
women is 270mg/day.
Sources: It is a component of chlorophyll, so green vegetables are a rich
source. Meat, pulses and cereals are also useful sources.
Deficiency: Deficiency rare in healthy individuals. Hypemagnesiumaemia can
occur as a result of high intestinal losses, increase urine excretion or as result
of certain diuretic drugs. Symptoms include muscle weakness, cramps,
hypertension and cardiac arrhythmias.
Toxicity:Toxicity is rare as surplus Mg is normally excreted by kidneys
rapidly. Can result in renal failure or overdose by IV administration.
Sodium & Potassium
• See previous notes in water lecture
Iron
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Function: The major role of iron is as an oxygen carrier in haemoglobin in blood and myoglobin in
muscle.
Requirement: About 1mg of iron per day is lost from the body via urine, faeces and sweat.
Menstruation accounts for losses of 20mg/month in women.This varies considerably and will be
increased in women with menorrhagia. Additional iron is required to meet the demands of
adolescence & pregnancy. The minimum requirement for iron therefore is 1mg/day in adult males,
3mg/day in adult females, taking account of the fact that only 5-10% of dietary iron is absorbed.
However the body has the capacity to absorb extra iron in times of greater physiological needs e.g.
acute blood loss, pregnancy.
Sources: dietary iron exists as 2 forms, haem and non-haem. Haem iron is contained in the
haemoglobin and myoglobin molecules of animals. This form is more bioavailable than non-haem
which is found in plant sources, e.g. spinach, cabbage leaves, beetroot. Interactions with other dietary
factors such as phytates (fibre) and tannins (tea) can reduce bioavailability of non-haem iron. On the
other hand vitamin C enhances iron absorption.
Deficiency: iron deficiency anaemia- manifested by breathlessness, weakness, tiredness, pale
colouring. Marginal deficiency very common in western world.
Toxicity: Not normally a problem from dietary sources. Supplementation however can override
normal homeostatic control and result in iron overload,, leading to interference with absorption of
other nutrients. Very large doses can be fatal. Mention haemechromatosis.
Zinc
• Functions: Zinc has a wide range of biological functions: it participates
in carbohydrate, lipid, protein and nucleic acid synthesis and
degradation. It also plays a structural role in non-enzymatic proteins
such as insulin and growth hormones. The human body contains about
2g of zinc, of which 60% is present in muscle tissue, 30% is in bone
and 5% is in skin.
• Requirement: Adult males RNI IS 9.5mg/day, Females 7.0mg/day.
• Sources: Rich sources red meat, fish and shell fish, milk and its
products, poultry and eggs.
• Deficiency: Because of its importance in protein, enzyme, and
nucleotide synthesis, the effects of deficiency are mst apparent in
rapidly dividing tissues, such as the mouthy, skin and intestinal
mucosa. Wound healing may be affected.
• Toxicity: Excesses of 2g/day can cause nausea and vomiting.
Copper
• Functions: Copper is involved in the renal and hepatic metabolism of
uric acid. It also contributes to elasticity and tensile strength of elastin
and collagen particularly in blood vessels.
• Requirement:Very limited data available on DRVs.Recommended
adult intake is approximately 1.5mg/day.
• Sources: Concentrated sources are shellfish, liver, nuts and cocoa.
• Deficiency: Rare. Marginal copper deficiency may be implicated in
CHD. Research continuing at present.
• Toxicity: Rare but have been reported in contamination of drinking
water resulting in gastrointestinal upset
Selenium
• Functions: Selenium has generated great interest recently
because of its anti-oxidant roles and hence potential
protective effect in Coronary Heart Disease and cancer.
• Requirement: Based on limited data. RNI approximately
70µg/day.
• Source: widely distributed but is greatly affected by soil on
which crops are grown. Mainly derived from meats, fats,
vegetables and cereals.
• Deficiency: intakes of < 12µg/day can cause Keshan
disease, a cardiomyopathy seen in China.
• Toxicity: Over-supplementation may be hazardous.
Fluorine
• Functions: It is incorporated into teeth and bones. It
incorporation into teeth enamel increases its hardness and
resistance to decay.
• Requirement: there is no established RNI, but COMA have
endorsed the fluoridation of water at 1part per million
(ppm) as a public health measure
• Sources: fluoridated water is our major source of fluoride
• Deficiency: Has never been demonstrated in humans.
However low levels of fluoride in water is associated with
increased risk of dental caries.
• Toxicity: Excessive intake may cause fluorosis (mottling
and discolouration of teeth)
Iodine
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Functions: Iodine functions as part of the thyroid hormones thyroxine and
triiodothyroxine. These are necessary for the maintenance of metabolic
processes, thermoregulation, protein synthesis and the integrity of connective
tissue. In the foetus, protein synthesis is dependent on iodine.
Requirement: Limited data available but 70µg/day appears to be enough to
prevent goitre so as a safe margin of error the RNI was set at 140 µg/day
Sources: Milk, sea foods and dried seaweeds are concentrated sources.
Deficiency: Deficiency in adults causes a fall in the blood level of thyroxine,
which in turn stimulates thyroid -stimulating hormone (TSH). TSH causes
hyperplasia of the thyroid gland and the development of goitre. In pregnancy
deficiency is associated with increased risk of still births and congenital
abnormalities. In children iodine deficiency is associated with mental
retardation, hypothyroidism and dwarfism.
Toxicity: Persistently high levels can cause hyperthyroidism which may be
linked to thyroid cancer.
Others
• Chromium - role in lipid and amino acid metabolism
• Manganese - many enzymes require manganese as part of their
structure. Is also a component of bone cartilage
• Molybdenum - is a cofactor in the enzymes involved in metabolism of
DNA
• Cobalt - is a cofactor for vitamin B12.
Fortification & Supplementation
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Todays busy lifestyle has lead to the more widespread use of convenience
foods which are not as high as fresh produce in micronutrients. This means
that the general population may not be consuming diets adequate in essential
macronutrients. Hence the use of micronutrients supplements by individuals
has greatly increased over the past 10 years. In addition mass fortification of
foodstuffs has become widespread. There are practices which are becoming
more widespread all the time in an attempt to optimise micronutrient status.
Some are mandatory as directed by government bodies and expert groups like
the folic acid fortification of flour in the UK & USA in an attempt to prevent
neural tube defects. Other are directed by industries for e.g. Kellogs undertook
fortification of a range of breakfast cereals about 15-20 years ago in order to
replace the B-vitamins lost during the processing of cereal grains. This move
resulted in spina bifda incidence dropping from 15 per 1000 births in Ireland to
2 per 1000 in the first year. This has now become a big marketing strategy and
many other companies have followed suit, with products such as supermilk
and breads being heavily fortified.
References
• 1) Department of Health (1991). Dietary Reference Values for
Food Energy and Nutrients for the United Kingdom. HMSO,
London.
• 2) Gissler (2011). Human Nutrition page 3. Page 197.
• 3) MJ Gibney, HH Voster, KJ Kok (2002). Introduction to
Human Nutriton. Blackwell Publishing.
Thursday coming
• Emer Bateman on weight reducing diets
• Next week – we are covering research
methods in nutrition