Download Food Constituents [continued] Micronutrients

Food Constituents [continued]
Micronutrients
VITAMINS
Vitamins are essential organic compounds needed for body functioning
and metabolism. They are classified into:
• Fat-soluble: A, D, E and K.
• Water-soluble: B group and C.
Vitamin A
Vitamin A is the name of a group of fat-soluble retinoid, including
retinol, retinal, retinoic acid, and retinyl esters .Vitamin A is involved in
immune function, vision, reproduction, and cellular communication.
Vitamin A is critical for vision as an essential component of rhodopsin, a
protein that absorbs light in the retinal receptors, and because it supports
the normal differentiation and functioning of the conjunctival membranes
and cornea. Vitamin A also supports cell growth and differentiation,
playing a critical role in the normal formation and maintenance of the
heart, lungs, kidneys, and other organs.
Two forms of vitamin A are available in the human diet:
1. preformed vitamin A (retinol and its esterified form, retinyl esters
2. provitamin A carotenoids .
Preformed vitamin A is found in foods from animal sources,
including dairy products, fish, and meat (especially liver). By far the
most important provitamin A carotenoid is beta-carotene; other
provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin.
The body converts these plant pigments into vitamin A. Both
provitamin A and preformed vitamin A must be metabolized
intracellularly to retinal and retinoic acid, the active forms of vitamin
A, to support the vitamin's important biological functions .
Vitamin A is obtained from dietary sources, and nondietary when
necessary.
1- Dietary Sources: animal and plant foods.
Animal foods: liver and liver product , egg yolk, whole-milk
and cheese, butter, cream, fatty fish, and any animal fat.
Plant foods: not provide vitamin A, but the vitamin precursor
{provitamin}. Carotenes are found in pigments of most vegetables
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and fruits {green, yellow, and red, orange:- carrots , red peppers ,
tomatoes ) . Beta – carotene in chlorophyll of dark – green leafy
vegetables ( spinach ) is particularly important.
2- Non dietary Source: cod-liver oil and other fish-liver oils can be
given to supplement vitamin A for vulnerable groups when
necessary.
Physiological Functions
1-Normal growth of healthy epithelial cells, of Skin and muous
membranes, especially of respiratory passages and urinary tract.
vitamin A is known as "anti-infection vitamin", because it is needed for
formation of healthy epithelial surfaces, which are the first line of natural
barriers of infection that resists invasion by pathogenic organisms. But
once infection occurs, vitamin A has no effect against infection {i.e. antiinfection role is preventive, not therapeutic}.
2-vitaminA is essential for the production of rhodopsin in the
rods 0f the retina., which is important for the adaptation of
vision in the dark.
3-growth
4-cell differentiation
5-Emberyogenesis\
6-Immun response
Deficiency vitamin A
• Eye changes : night blindness when vitamin A status is
marginal , and with prolonged or sever deficiency , changes to
the cornea and congunctiva occur , these eye changes are
known collectively as Xerophthalmia . these changes consist
of conjunctival xerosis and lack of tears , Bitot`s spots , corneal
xerosis , corneal ulceration and corneal scars
• Epithelial tissues – skin keratinization , horny plugs block the
sebaceous glands leading to follicular hyperkeratosis
• Immunity : vitamin A deficiency results in increase
susceptibility to infectious diseases such as diarrhea and
respiratory infections due to Pathological changes of mucous
membranes that become more susceptible to infection.
Requirements :
The established recommended dietary allowance standard for
adults is 800 µg for women and 1000 µg for men.
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Table 1: Recommended Dietary Allowances (RDAs) for Vitamin A
Age
Male
Female
Pregnancy
Lactation
0–6 months* 400 mcg RAE 400 mcg RAE
7–12 months* 500 mcg RAE 500 mcg RAE
1–3 years
300 mcg RAE 300 mcg RAE
4–8 years
400 mcg RAE 400 mcg RAE
9–13 years
600 mcg RAE 600 mcg RAE
14–18 years
900 mcg RAE 700 mcg RAE 750 mcg RAE 1,200 mcg RAE
19–50 years
900 mcg RAE 700 mcg RAE 770 mcg RAE 1,300 mcg RAE
51+ years
900 mcg RAE 700 mcg RAE
RDAs for vitamin A are given as mcg of retinol activity equivalents (RAE) to account
for the different bioactivities of retinol and provitamin A carotenoids
Pregnant and Lactating Women in Developing Countries
Pregnant women need extra vitamin A for fetal growth and tissue maintenance and for
supporting their own metabolism. The World Health Organization estimates that 9.8
million pregnant women around the world have xerophthalmia as a result of vitamin
A deficiency .Other effects of vitamin A deficiency in pregnant and lactating women
include increased maternal and infant morbidity and mortality, increased anemia risk,
and slower infant growth and development.
The most common and readily recognized symptom of vitamin A deficiency in infants
and children is xerophthalmia
Vitamin D ( calciferols )
{Antirachitic Vitamin}
What is Vitamin D?
Vitamin D is a fat-soluble vitamin that's formed when skin is exposed to the sun's
ultraviolet rays. Vitamin D is also found in food and dietary supplements.
There are two major types of vitamin D. Vitamin D3, also called cholecalciferol, is
the type made in the body in response to sun exposure and found in certain foods.
Vitamin D2 (ergocalciferol) is the most common form used in supplements. It's also
used to fortify certain foods, such as milk.
Both typ\es of vitamin D must be converted in the liver and kidneys to the active
form, 1,25 dihydroxyvitamin D, to be useful to the body.
Present in two forms: Vitamin D2 and Vitamin D3.
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Dietary ergocalciferol and cholecalciferol are biologically inactive
and are activated to 25- hydroxyvitamin D in the liver ( this has
limited amount of biological activity ) . further conversion in the
kidney in the production of more active form 1,25dihydroxyvitamin D ( Calciferol)
Sources of Vitamin D:
1- Dietary Sources:
• Oil-rich salt-water fish {e.g. sardines and salmon}, liver, egg yolk ,
, and other fat-containing animal foods: provide but little vitamin
D, not satisfying body need.
• Cod liver oil
• D-fortified foods {vitamin D is added}: baby powder milk, and
fortified butter and margarine.
2- Non dietary Sources: vitamin D supply is largely nondietary.
a) Ultraviolet radiation of skin:
Exposure of bare skin to sunlight.
Exposure to artificial ultraviolet rays:
only occasionally used to treat rickets, if
necessary.
b) Medicinal preparation of oral fish liver oil {provide
vitamin D and A}, or vitamin D2, oral or parenteral,
given, to supplement vitamin D
What Does Vitamin D Do?
The main function of vitamin D is to maintain normal levels of calcium and
phosphorus in the blood to support bone mineralization (hardening of bones), cell
functions, and proper nerve and muscle function. Vitamin D acts as a hormone,
enhancing the absorption of calcium and phosphorus in the small intestine.
Vitamin D is needed for normal growth. Without it, bones become weak and
deformed, resulting in rickets in children and a condition called osteomalacia in
adults.
• Osteoporosis
Vitamin D deficiency can lead to the development of osteoporosis because it reduces
calcium absorption. In older people, low vitamin D levels have been associated with
an increased risk of falling. Higher vitamin D levels have been associated with
stronger bones (greater bone mineral density).
• Cancer
Preliminary evidence suggests vitamin D may aid in cancer prevention by blocking
cell growth and differentiation (cells mature and take on a specialized form and
function).
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Since the late 1980s, the risk of developing and dying from breast, prostate, ovarian,
and other cancers has been found to be increased in geographic areas located at higher
latitudes, where there's less sun exposure, and with vitamin D deficiency.
• Autoimmune Disease
Because vitamin D is thought to influence the immune system, there is some evidence
it may help with autoimmune disease.
• Other Conditions
Preliminary evidence suggests vitamin D may help with muscle and bone pain,
diabetes prevention, fibromyalgiagum, mood disorders, and proper immune function.
Vitamin D supplements are also available. Multivitamins and calcium supplements
provide vitamin D, but the amount varies widely so it's important to read labels.
Vitamin D3 (cholecalciferol) is the preferred form.
Recommended Vitamin D Intake
recommendations for vitamin D intake are as follows:
•
•
•
•
Birth to 50 years -- 200 IU (5 mcg)
Between 51 and 70 years -- 400 IU (10 mcg)
Over 71 years -- 600 IU (15 mcg)
Pregnant and nursing women -- 200 IU (5 mcg).
In a recent study that found a 7% reduction in mortality, the average intake was about
500 IU per day.
Function:
Vitamin D is needed for bone metabolism:
• 1,25 dihydroxyvitamin D maintains plasma Ca by controlling
Ca absorption and excretion
• Vitamin D and it's metabolites are involved in bone
mineralization
Deficiency:
Arises mainly from nonexposure of bare skin to sunlight.
Blood calcium and phosphorus level in blood is inadequate for
mineralization of growing bone, and remineralization of mature bone,
causing:
• Rickets, (which is characterized by reduced calcification of
bone epiphyses) , and late eruption and early decay of teeth in
children.
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• Osteomalacia in adults: largely due to calcium deficiency, and
occasionally vitamin D deficiency.
• Osteoporosis: vitamin D deficiency may contribute to type II
Osteoporosis of the elderly.
Vitamin E
Eight naturally occurring forms of Vit E are synthesized in plants
Sources:
• Wheat- germ oil
• egg yolk and liver are rich sources.
• Almonds.
• sunflower seeds and oil
• peanuts and peanut butter
• corn oil
Recommended daily allowance: the recommended daily allowance
( RDA) standard for men and women age 14 and older is 15 mg / day ,
with lesser amounts required in childhood. Needs during the first year of
infancy do not have an RDA figure, but an adequate intake amount of 46 mg/day is used .The UL ( Tolerable Upper Intake Level) for adults is
set at 1,000 mg /day .
Function :
• Antioxidant, vitamin E is a powerful antioxidant and protects
cell membranes and lipoproteins from damage by free radicals
• Maintenance of cell membrane integrity
• Regulation of prostaglandin synthesis
• DNA synthesis
Vitamin K
Naturally occurring vitamin K can be classified into two groups ,
the major form of vitamin K 1 is found in plants while the vitamin
K2 group of compounds are synthesized by intestinal bacteria
Sources:
Dietary: fresh dark- green leafy vegetables (spinach, cabbage ).
Biosynthesis: intestinal flora form vit. K.
Synthetic preparations: of K3, oral and parental therapeutic purposes.
Function
• Blood clotting : vitamin K is essential for maintaining normal
levels of four of the 11 blood clotting factors. promotes the
synthesis of γ - carboxyglutamic acid ( Gla ) in the liver . Gla is
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an essential part of prothrombin ( factor II ) and other
coagulation factors ( VII, IX , and X ) .vitamin K is therefore
essential for blood coagulation
• Bone development: spesific proteins found in bone and bone
matrix require vitamin K for their synthesis and are involved
with calcium in bone development ,these bone proteins bind
calcium but function here to form bone crystals .
Deficiency:
• Lower prothrombin level in blood, resulting in prolonged clotting
time, and defective coagulation of blood, with increased tendency
to bleeding on injury.
• New born babies are given an injection of vitamin K at birth ,
infants are born with very low stores , due to sterility of
their intestines do not have bacteria producing vitamin K
Requirement
It is suggested that the requirement are between 0.5 and 1.0
µg per kg \d , RDA standard for men is 80 µg \d
for women 65 µg \d
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