Transcript Chapter 7: Proteins - University of Akron

Vitamins: An Overview
Vitamins
Essential organic substances (contain
carbon)
– Not synthesized
– Inadequate synthesis
Yield no energy, but facilitate energyyielding chemical reactions
If absent from a diet, it will produce
deficiency signs and symptoms
Body Needs Vitamins for Normal
Function
Growth
Maintenance
Reproduction
Two Forms of Vitamins
Precursor/Provitamin
– Dietary form inactive
– Activated in body
Active form
– Dietary form active
– Not changed in body
Vitamins Often Serve as
Coenzymes
Vitamin Classification
Fat-soluble vitamins
– Dissolve in substances such as ether and
benzene but not readily in water
– Include vitamins A, D, E, and K
Water-soluble vitamins
– Vitamins that dissolve in water
– Include B vitamins and vitamin C
Vitamin Classification
Category determines
Food sources
How handled in body
Best preservation methods
Vitamin History
First discovered: fat soluble substance essential
for health in 1912-1914 (vitamin A)
B complex: 1915-1916 (water soluble nutrient)
Vitamin C: isolated 1912
Vitamin D, Vitamin E: 1922
Last vitamin (B12) discovered in 1948
Likely all vitamins have been discovered, since
people can be maintained on IV solutions
fortified with known vitamins
Vitamin Facts
Megadose (>10x needs) proved useful in
treating certain conditions
Plant and animal foods provide vitamins
Synthesized vitamins work equally well in
the body
Fat-Soluble Vitamins
Dissolve in organic solvents
Not readily excreted; can cause toxicity
Absorbed along with fat
– Deficiency with fat malabsorption
– Fat blockers (Orlistat/Xenical)
– Mineral oil
Fat Soluble Vitamins
Requires protein carrier
– Transported like fat in chylomicrons, VLDL,
LDL
Stored in body (except Vitamin K)
– Fat tissue/liver
– Can cause toxicity
– Vitamin D and A most likely to be toxic
Fat Soluble Vitamin Preservation
Not easily destroyed
Fat addition in cooking vegetables
– Fat soluble vitamins leach out
– Lost if liquid discarded
– Add fat after vegetables drained, just before
serving
Baking soda
– Used to preserve color of green vegetables
– Destroys Vitamin D
Water Soluble Vitamins
Found in grains, fruits, vegetables, meat
Low risk of toxicity
– Not stored in large amounts
– Excess excreted inurine
– Need daily intakes
Easily destroyed
– Heat – increases enzyme activity
– Light – destroys riboflavin
– Oxygen: breaks down
Water Soluble Vitamins Preservation
Cooking
– Heat – destroys vitamins
– Water – leaches out vitamins
– Baking soda – destroys thiamin
Conserve vitamins
– Store foods covered in refrigerator
– Consume soon after purchase (freshest
possible)
– Minimal cooking/minimal liquid
– Freezing preserves vitamin content
Vitamin A
Deficiency is most common cause of nonaccidental blindness worldwide
Up to 500,000 children in developing nations
especially Asia, become blind each year
because of Vitamin A deficiency
Functions of Vitamin A
Prevents night blindness
Prevents xerophthalmia (dry eye)
Maintains cell health (epithelial cells)
Growth, development, reproduction
Cardiovascular disease prevention
Cancer prevention
Night Blindness
Vitamin A is needed for dark vision
Rhodopsin in retina
– Light destroys
– Constantly reformed
Allows for a chemical process to signal the
brain that light is striking the eye
Allows eyes to adjust to dark vision
Xeropthalmia
In Vitamin A deficiency, the cells that line
the cornea lose their ability to produce
mucus
When dirt particles scratch the dry surface
of the eye, becomes infected
Leads to blindness
Worldwide public health efforts are
fortifying sugar, margarine, MSG, giving
large doses of Vitamin A 2x year
Macular Degeneration
Leading cause of legal blindness among North
American adults over 65
Changes in the macular area of the eye
Age, smoking, and genetics are risk factors
Macula contains carotenoids lutein and
zeaxanthin
High intakes of carotenoids associated with
lower risk (but may be fruit and vegetable intake)
Also may reduce risk of cataracts
Multivitamins are adding lutein
Cell Health
Vitamin A maintains health of cells that
line internal and external surfaces
(epithelial cells)
Barriers to bacterial infections
Epithelial cells produce mucus
Without vitamin A, these cells do not
produce mucus
Increases infections and decreases
immune system
Growth
Vitamin A binds to DNA
Assists in protein synthesis
Affects growth, reproductive system, and
bone growth
Cancer and Cardiovascular
Disease
Role in cell development and immune-system
Role as an antioxidant
Lower risk of breast cancer with vitamin A
supplements
Megadoses are not recommended
Mixed results in cancer/vitamin A studies
Foods rich in vitamin A and other
phytochemicals are advised
Prostate Cancer and Carotenoids
One of the most common cancers among
North American men
Lycopene (tomatoes, watermelon, other
fruits) seems to protect against it, possibly
due to antioxidant activity
Vitamin A and Your Skin
Topical treatment and oral drug
Accutane (oral) and Retin-A (topical)
Can induce toxicity symptoms
Contraindicated in pregnant women
Use only under supervision of a physician
Sources of Vitamin A
Preformed
– Liver, fish oils, fortified milk, eggs
– Contributes to half of vitamin A intake in North
America
Provitamin
– Dark leafy green, yellow-orange
vegetables/fruits; carrots, spinach and other
greens, winter squash, sweet potatoes,
broccoli, mangoes, cantaloupe, peaches and
apricots
– Contributes to half of all the vitamin A intake
Vitamin A from the Food Guide
Pyramid
Deficiency of Vitamin A
Night blindness
Decrease mucus production leading to
bacterial invasion in the eye
Irreversible blindness
Deficiency of Vitamin A
Follicular hyperkeratosis
Keratin protects the inner layers of skin
and maintains moisture
Kertinized cells replaces the normal
epithelial cells in the underlying skin layers
Hair follicles become plugged
Bumpy, rough, and dry skin
Measuring Vitamin A
International unit (IU)-crude method of
measurement
Retinol activity equivalent (RAE) current, more precise method of
measurement
1 ug of retinol = 1 RAE = 3.3 IU =12
ug beta-carotene = 24 ug of other
provitamin A
RDA for Vitamin A for Adults
900 mcg REA for men
700 mcg REA for women
Average intake meets RDA
Daily value used on food and supplement
labels is 1000 mcg
Much stored in the liver
Vitamin A supplements are unnecessary
No separate RDA for carotenoids
Who is at Risk For Deficiency
Breast fed infants
Preschooler with poor vegetable intake
Urban poor
Elderly
Alcoholics and people with liver disease
Individual with fat malabsorption
HIV, AIDS
Toxicity of Vitamin A
Large intake of vitamin A over a long
period: supplements, liver, fish oil
Bone/muscle pain, loss of appetite, skin
disorders, headache, dry skin, hair loss,
increased liver size, vomiting
Possible permanent damage
Discontinue supplement
Toxicity of Vitamin A
May produce fetal malformations and
spontaneous abortions in pregnant women
May occur with as little as 3 x RDA of
preformed vitamin A
Pregnant women and women who may
become pregnant should limit to 100% DV
Upper Level for Vitamin A
– 3000 ug for adults
Fatal dose -12 g of vitamin A can be fatal
Toxicity of Carotenoids
Don’t produce toxic effects
because
– Rate of conversion to Vitamin A is slow
and regulated
– Efficiency of absorption decreases as
oral intake increases
Carotenoids
High amounts of carotenoids in the
bloodstream
Excessive consumption of
carrots/squash/beta-carotene
supplements
Skin turns a yellow-orange color
Vitamin D
Prohormone
Derived from cholesterol
90% of needs is synthesized from sun
exposure
Insufficient sun exposure makes this a
vitamin
Sun Exposure to Prevent
Vitamin D Deficiency
~15 minutes 2-3 times a week
Between 8 a.m. and 4 p.m.
Hands, face, arms
Light skin
No sunscreen greater than SPF8
Activation of Vitamin D
To become the active hormone, Vitamin D
must be
Acted on by the liver to produce 25hydroxyvitamin D
Acted on by the kidney to produce 1,25
dihydroxyvitamin D (active hormone form)
Functions of Vitamin D
Regulates blood calcium
– Regulates calcium and phosphorus
absorption from the intestine
– Reduces kidney excretion of calcium
– Regulates calcium deposition in bones
– Serum calcium involved in nerve transmission
and muscle contraction
Functions of Vitamin D
Influences cell differentiation
– Linked to reduction of breast, colon, and
prostate cancer
– Controls the growth of the parathyroid gland,
aids in immune function, contributes to skin
cell development
Role in Bone Formation
Vitamin D causes Ca + Phos to deposit in
the bones
Strengthen bones
Food Sources of Vitamin D
Fatty fish (salmon, herring)
Fortified milk and yogurt
– 10 mcg per quart in US and Canada
Some fortified cereal
The Adequate Intake (AI) for
Vitamin D
5 ug/d (200 IU/day) for adults under age
51
10-15 ug/day (400 - 600 IU/day) for older
Americans
Light skinned individuals can produce
enough vitamin D to meet the AI from
casual sun exposure
Infants are born with enough vitamin D to
last ~9 months of age.
Vitamin D Toxicity
Upper level is 50 mcg/day
Vitamin D can be very toxic especially in
children
Regular intake of 5-10x the AI can be
toxic
Results from excess supplementation
(not from sun exposure or milk
consumption)
Vitamin D Toxicity
Signs/symptoms: overabsorption of
calcium (hypercalcemia)
Signs of high blood calcium: weakness,
loss of appetite, diarrhea, vomiting, mental
confusion, increased urine output
Calcium deposits in kidneys, heart, and
blood vessels
Mental retardation in infants
Vitamin D Deficiency
At risk
Dark skinned
Lack of sun exposure
Northern climates in wintertime
Breastfed babies
Vitamin D Deficiency: Rickets
Is the result of vitamin D deficiency in
children
Poor mineralization of bones because of
low calcium content
Fortification of milk has greatly reduced
rickets in children
Most rickets is associated with fat
malabsorption, as in cystic fibrosis
Vitamin D Deficiency:
Osteomalacia (soft bone)
Is rickets in the adult
Low calcium content in bones due
to lack of vitamin D
Vitamin E
Group of fat-soluble compounds,
tocopherols and tocotrienols
Alpha-tocopherol is the most potent
Fat-soluble antioxidant
Resides mostly in cell membranes
Redox Agent
Vitamin E is able to donate electron to
oxidizing agent
Protects the cell from attack by free
radicals
Protects PUFAs within the cell membrane
and plasma lipoproteins
Prevents cell death
Prevents the alteration of cell’s DNA and
risk for cancer development
Vitamin E, An Antioxidant
The More The Better?
Vitamin E is only one of many antioxidants
It is likely that the combination of
antioxidants is more effective
Best to diversify antioxidant intake with a
balanced and varied diet
Megadose of one antioxidant may interfere
with the action of another
Vitamin E and Cardiovascular
Disease
Epidemiological studies suggest higher intakes
of Vitamin E are associated with lower risk of
CHD
Clinical trial results have been mixed
American Heart Association states it is
premature to recommend vitamin E supplements
to the general population
FDA has denied permission for supplement mfr’s
to claim that Vitamin E prevents heart disease
and cancer
Other Functions of Vitamin E
Protects the double bonds in saturated fat
Helps vitamin A absorption
Role in iron metabolism
Inhibits LDL oxidation
Maintenance of nervous tissue and
immune function
Food Sources of Vitamin E
Plant oils: salad dressings, mayonnaise
Fortified cereals, oatmeal
Wheat germ
Asparagus, tomatoes, green leafy
vegetables
Food Sources of Vitamin E
Peanuts
Margarine
Nuts and seeds (sunflower seeds)
Actual amount is dependent on
harvesting, processing, storage and
cooking
Food Sources of Vitamin E
Vitamin E: Easily Damaged
Oxygen
Metals
Light
High heat
– Deep fat frying
RDA for Vitamin E
15 mg/day alpha-tocopherol for women
and men
(=22 IU of natural source or 33 IU of
synthetic form)
Average intake meets RDA
1 mg d--tocopherol = 0.45 IU (synthetic
source)
1 mg d--tocopherol = 0.67 IU (natural
sources)
Deficiency of Vitamin E
Hemolytic anemia
Hemolysis occurs in preterm infants
because they did not receive enough
vitamin E from their mothers
Preemie formulas and supplements
compensate for increased needs
Deficiency of Vitamin E:
Who’s At Risk?
Smokers are especially at risk (smoking
destroys vitamin E in the lungs)
– However even megadoses may not prevent
damage
Adults on very low fat diets
Fat malabsorption
Toxicity of Vitamin E
Supplements up to 800 IU probably
harmless
Upper Level is 1,000 mg/day of any
form of supplementary alpha-tocopherol
Upper Level is 1500 IU (natural
sources) or 1100 IU (synthetic forms)
Inhibits vitamin K metabolism especially
in conjunction with anticoagulants
Possible hemorrhage
Vitamin K (“Koagulation”)
Family of compounds found in plants,
plant oils, fish oils, and meats
Synthesized by the bacteria in the colon
and are absorbed (10% of needs)
Role of Vitamin K
Role in the coagulation process
– Contributes to the synthesis of several bloodclotting factors
Helps form proteins present in bone,
muscle, and kidneys
– Imparts calcium-binding potential
– Poor intake linked to increase in hip fractures
Vitamin K in Newborns
Newborn’s intestinal tract lacks bacteria to
allow blood to clot effectively
Vitamin K is routinely given by injection
shortly after birth to bridge the gap
May also occur in adults with chronic
malabsorption
Drugs and Vitamin K
Anticoagulant
– Lessens vitamin K reactivation
– Lessens blood clotting process
– Monitor vitamin K intake
Antibiotics
– Destroy intestinal bacteria
– Inhibit vitamin K synthesis and absorption
– Potential for excessive bleeding
Food Sources of Vitamin K
Liver
Green leafy vegetables
Broccoli
Peas
Green beans
Soybeans/canola oil
Resistant to cooking losses
Limited vitamin K stored in the body
Adequate Intake for Vitamin K
90 ug/day for women
120 ug/day for men
Amount met by most
Excess vitamins A and E interferes with
vitamin K
Newborns are injected with vitamin K
(breast milk is a poor source)
Toxicity unlikely; readily excreted
Next: Water Soluble Vitamins