Transcript Kin 110 Lecture 6

Kin 110 Lecture 6
Vitamins Ch. 8
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Learning Objectives
• Define vitamin
• Classify vitamins as fat-soluble or
water-soluble
• List the major functions and
deficiency symptoms for each fatsoluble vitamin
• List three important food sources for
each fat-soluble vitamin
• Describe toxicity symptoms for
excess consumption of certain fatsoluble vitamins
• Evaluate the use of vitamin
supplements - risk / benefit
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Vitamins
• Vitamin – essential organic (contains
carbon) substances needed in small
amounts in diet
• Required for normal function,
growth, maintenance of body
structures
• Yield no energy, but participate in
energy yielding reactions
• fat soluble vitamins - ADEK
• water soluble vitamins-B vitamins and C
• co-enzymes – help enzymes function
– B vitamins and vitamin K
– Fig. 8-1
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Vitamins
• To be classified as vitamin
– Body unable to synthesize enough
– Absence for a defined period of time
must produce deficiency (fig 8.2)
– symptoms, if caught in time, are cured
when substance is reintroduced to diet
• Megadoses of Vitamins
– Requires Medical supervision
• Toxicity diseases are possible
• Many unproven claims continually being
made
– Niacin - cholesterol lowering
– Vit D - treatment of psoriasis
• Have they all been found?
– People living on intravenous solutions
of Protein, Carbohydrates, Fat and all
known vitamins and minerals survive,
grow, reproduce and fight disease
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Storage of Vitamins
• Fat soluble vitamins A, E and D
not readily excreted
• Water soluble - lost from body
quite rapidly (B6 and B12 stored)
• In general, limited storage of
vitamins
– should be consumed daily
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Vitamin Toxicity
• Toxicity theoretical for all vitamins
• Fat soluble more frequently observe
toxicity (A and D)
• E, Niacin, B-6 and C – very large
amounts needed to result in toxicity
– Only possible from supplements
• A and D only 3-5 times RDA needed
on a regular basis for toxicity
– Vit A – important to minimize in early
pregnancy
– Once a day vitamins, less than 2 times
daily value – not a risk
• Preserving vitamin content - Table 8.1
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Fat soluble Vitamins
• ADEK
– Table 8.2
• Absorbed along with dietary fat
• Travel in bloodstream along with fat
to reach body cells
• Stored in liver and fatty tissue
• 40-90 % of fat sol. vit. absorbed
• Can be reduced further –
interference in normal digestion and
absorption of fats.
– Eg. Mineral oil laxatives
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Vitamin A
• Easy to over dose (toxic) and be
deficient
– Both cause severe problems
• Variety of forms
• Retinoids
– Preformed vitamin A –
– Only found in animal foods
• Carotenoids – pro-vitamin A
–
–
–
–
plants
Yellow-orange pigment in carrots
Turned into vitamin A as needed
Most potent form is beta-carotene
• Both pre and pro – referred to as
Vitamin A
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Functions of Vitamin A
• Many roles – not all well understood
• Role in vision – best known and
most clearly understood
– Performs important functions is both
light (day) and dark (night) vision
– in dim light, one form of A is required
to start the chemical process that signals
the brain that light is striking the eye.
• Without vit A – night blindness
• Prolonged deficiency – cells unable
to produce mucus for cornea
– Dry, dirty, scratched, infected
– Xeropthalmia - dry eye
• Less-developed nations – children
– Blindness. Infection, death
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Health of Cells
• Vitamin A – maintains health of all
cells that line internal and external
surfaces
– Lungs, intestines, stomach, eyes, skin
(epithelial cells)
– Cells secrete mucus – lubricant
– Without A – decrease activity of
immune cells, increased infection
• Carotenoids play a role in preventing
cardiovascular disease
• Needed for growth, Development
and Reproduction
– Synthesis of proteins that stimulate
proper growth and development
– Resorbing and producing bone
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Cancer and Vitamin A
• Skin, lung, bladder and breast cancer
• Adequate intake of vitamin A can
lower risk of breast cancer
– Megadoses NOT recommended to
prevent cancer
• Carotenoids – trap energy in free
radicals – oxidation can initiate
cancer process
– Supplements of b-carotene not
effective
– Variety of fresh fruits and vegetables
– Lycopene - tomatoes - may prevent
prostate cancer
• Acne – topical and internal derivatives
– May produce birth defects in pregnant
women using treatments
– Eg retin-A and accutane
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Vitamin A in Food
• Preformed vitamin A
– liver, fish oils, fortified milk and cereal,
butter, margarine, eggs
• Pro-vitamin – dark green and orange
vegetables
– Carrots, spinach, winter squash,
papaya, apricots, sweet potatoes
• RDA – RAE- retinol activity equivalent
– 900 mg RAE (males)
– 700 mg RAE (females)
• Due to difficulty in classifying
contributions from preformed and
pro-vitamin A sources the labeling
has undergone changes recently
– Very old - IU, old RA, now RAE
• Risk of deficiency – children, poor,
alcoholics
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• Dietary sources table – fig 8.3
Toxicity of Vitamin A
• 3 times the RDA can cause problems
if continued for prolonged periods
• Early pregnancy (pre-formed)
– Fetal malformations, birth defects,
spontaneous abortion
• Non-pregnant – skin, hair, internal
organs and CNS
– Permanent damage can occur
• Vit A is stored for months
– Women in childbearing years – limit to
100% intake -one ounce of liver - 300%
• Carotenoids (pro form) not toxic
– Rate of conversion is slow
– Efficiency of absorption decreases as
intake increases
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Vitamin D
• Also considered a hormone
– skin cells convert cholesterol like
substance into vitamin D using
sunlight
• effects kidney and bone
• 10-15 minutes of exposure of
arms, face and hands; 2-3 times
per week
– not effective in winter
– must have vitamin intake
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Functions of Vitamin D
• To become active hormone, vitamin
D must be activated in liver and
kidneys
• calcitrol - active form
• regulates calcium and bone
metabolism along with parathyroid
hormone
– regulates absorption of calcium and
phosphate from intestines
– reduces kidney excretion of calcium
– regulates deposition of calcium in
bones
• Immune system and skin development
influenced by vitamin D
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Vitamin D and Bone
• Calcium and phosphorus deposition
• without vit D bones weaken and bow
under pressure
– Rickets (children)
– fortification of milk – malabsorption of fat (cystic fibrosis)
• osteomalacia - adults - soft bones
–
–
–
–
–
–
calcium withdrawn from bones
inefficient absorption or conservation
vit D deficient
bones porous and weak - break easily
supplement vit D - reduces fractures
problem with vitamin D activation or
absorption
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Dietary Sources of D
• Fatty fish (sardines, salmon),
fortified milk, yogurt and cereals
–
–
–
–
under 51 years - 5 mg/day
over 51 2-3 times - 10-15 mg/day
max. 50 mg /day
Young, fair skinned 10-15 min of sun
on face and arms 2-3 times /week
• 5-10 times recommended on regular
basis results in toxicity
– calcium over absorption - deposition in
kidneys and other organs
– high blood calcium
– Weakness, loss of appetite, diarrhea,
vomiting , mental confusion,
– sun exposure does not result in toxicity
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Vitamin E
• Fat soluble antioxidant • resides in cell membranes
• donates electrons - protection from
free radicals
• fig 8-4
• DNA oxidation - cancer, cell death
– repair mechanisms for damage
• impact on cancer, heart disease very
minimal compared to proper diet and
exercise
– not an alternative to making good
overall health choices
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Deficiency of vitamin E
• Few women getting enough vitamin
E from food
– Supplements not as potent
– Smoking destroys vitamin E
• Cell membranes break down
– red blood cell breakdown in infants
– unsaturated fatty acids susceptible to
oxidation
– hemolysis- breaking of rbc in absence
of vit. E
• vit E improves vit A absorption
• used to metabolize iron in cell,
maintain nervous tissue, and insulin
function
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Vitamin E in Foods
• plant oils, fortified cereals, fruits and
vegetables, eggs, margarine
– Sunflower seeds and almonds are an
excellent source of vitamin E
– vitamin E in plant oils - protects
unsaturated fatty acids
– Animal foods almost no vitamin E
• content of vit E depends on
harvesting , processing storage and
cooking
– easily destroyed by oxygen, metals ,
light , repeated frying
• RNI - 15 mg /day
• alpha tocopherol - most active form
• megadose therapy - not proven
– Upper level is 1000mg of supplement
– toxicity not a problem, except for
people on anticoagulants (CVD) or with
a vitamin K deficiency - due to
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increasesd risk of hemorrhage
Vitamin K
• Family of compounds known
collectively as vitamin K
• Found in plant oils, fish oils, and
meats
– One form is synthesized by bacteria in
the intestine (10% of need)
• role - vital for blood clotting
– synthesis of blood clotting factors
• formation of proteins in bone,
kidney and muscle
– impart calcium binding potential
• newborns lack bacteria to produce
vitamin K
– routine injection at birth
• deficiency in adults on prolonged
antibiotics or with poor fat absorption
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Vitamin K in Food
• Liver, green leafy vegetables,
broccoli, peas and green beans
– Also soybean and canola oils
• vitamin K not stored well - one day
– abundant in diet, deficiency uncommon
– resistant to cooking
• RDA - 90-120 mg / day
– no risk of toxicity
– risk of reduced effectiveness of
medications to reduce blood clotting
(CVD)
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Vitamin Supplements
• Supplements may be beneficial, and
improve health of population
– Most unwilling to increase intake of
fruits and vegetables
• folate (B vitamin)
– birth defects
– homocystien - risk factor for heart
disease
– alleviated by adequate folate (and
reduction in red meat)
• vitamin B12 - risk over 50
– synthetic more easily absorbed
• Eat right and take a multivitamin
– Use supplements in consultation with
physician
– Potential impacts of medications for
CVD and cancer
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Vitamin Supplements
• Megadoses of E and B12
– trials ongoing, may be beneficial
– Vit E not very exciting results
• Supplements should be taken with or
just after meal
• no more than 100% of daily values
– avoid excess selenium and C
• overabsorption of iron
– males avoid excess iron
– excess zinc - inhibits iron an copper
absorption
– excess folate - masks B12 deficiency
– avoid other products - PABA, inositol,
bee pollen, lecithin
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