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Transcript
Vitamins
• Are required for proper metabolism
• Do NOT directly provide energy
• Are necessary for obtaining energy from the
macronutrients
• Often function as coenzymes
Vitamin C
• Scurvy described as far back as 1500 BC
• 1757 Lind found that cider, vinegar, oranges,
lemons prevented scurvy
Antioxidant
• Ascorbic acid donates 2 hydrogens with their electrons to free radicals to
form dehydroascorbic acid
Functions
• Keeps iron and copper in reduced states
• Iron absorption
• Enhances immune function (WBC, balance of
phagocytosis)
• Synthesis of: Collagen (Fe), Carnitine (Fe),
Neurotransmitters (Cu), hormones
• Conversion of cholesterol to bile acids
• Linus Pauling – the common cold?
Collagen Synthesis
Cofactor and coenzymes
• Cofactor: a non-protein chemical compound
that is bound to a protein and is required for
protein’s biological activity.
• Cofactors are either organic or inorganic.
Cofactors are often classified as inorganic,
while coenzymes are often classified as
organic.
Water Soluble B Vitamins
Foods with B vitamins
• In general, B vitamins are found in a wide
range of foods
• B vitamins are more likely found in
foods of animal origins (B12), protein rich
foods, whole-grain foods, fortified foods
Keeping B Vitamins in Foods
• Easily destroyed by UV rays (sun), heat,
exposure to oxygen
– Implications for cooking and storage
• Water soluble
– They leach out of foods when washed and
cooked in water
B Vitamin Toxicity
• Some B vitamins are toxic if too much is
consumed:
– Niacin: Flush, Liver damage, Impaired
glucose regulation
– B6: Nerve degeneration, skin lesions
– Folate: Masks B12 deficiency
B Vitamin Deficiency Diseases
• With general B deficiencies, can see:
glossitis - smooth, glossy tongue due to
atrophy of the tissue
Enrichment act of 1941 and 1998
• Many nutrients lost through milling process of
grain
-germ, bran & husk layers removed
• Grain/cereal products are now enriched
• Thiamin, riboflavin, niacin, folate, iron
• Enriched grains still deficient in B-6,
magnesium and zinc
B Vitamins
•
•
•
•
•
•
•
•
Thiamin (B1)
Riboflavin (B2)
Niacin (B3)
Biotin (B7)
Pantothenic Acids (B5)
Pyridoxamine (B6)
Folate
Cobalamin (B12)
B Vitamins and Metabolism
• Act as coenzymes
- In reactions that:
1) Release energy from food
2) Regulate metabolism
- In cell multiplication
1) Red blood cells
2) Cells of the GI lining
Thiamine (= vitamin B1) phosphate derivatives of this vitamin are
involved in many cellular processes. The best-characterized form is
thiamine pyrophosphate (TPP), a coenzyme in the catabolism of sugars
and amino acids, also required in alcoholic fermentation
•a lack of thiamine can be caused by malnutrition, a diet high in
thiaminase-rich foods (raw freshwater fish, raw shellfish, ferns)
and/or foods high in anti-thiamine factors (tea, coffee, betel
nuts) and by grossly impaired nutritional status associated with
chronic diseases, such as alcoholism, gastrointestinal diseases
and AIDS
•Beriberi
•deficiency symptoms: Muscle wasting and nerve damage,
sometime edema, severe fatigue of eyes, neurodegeneration,
wasting, and death
•sources: yeast, pork and whole grains
Thiamin (TPP) - Vit B1
- involved in the cleavage of
bonds adjacent to a carbonyl
group:
-the conversion of pyruvate
to acetyl-CoA
thiamine pyrophosphate (TPP)
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.
Thiamin
Pork is the
richest source
of thiamin, but
enriched or
whole-grain
products
typically make
the greatest
contribution to
a day’s intake
because of the
quantities
eaten.
Riboflavin (= vitamin B2) is the central component of the cofactors FAD and FMN, and
is therefore required by all flavoproteins, which play key roles in energy metabolism,
and for the metabolism of fats, ketone bodies, proteins and
Carbohydrates
•Oxidation-reduction reactions
•Yellow enzyme – “fluorescent urine”
•deficiency is relatively rare and can be addressed with supplementation
•deficiency symptoms: Ariboflavinosis - Sore throat, swollen mucous
membranes, mouth or lip sores, anemia, and skin disorders
-alcoholics and phenobarbital use
•sources: milk, cheese, leafy green vegetables, liver, kidneys, legumes,
tomatoes, yeast, mushrooms, and almonds are good sources, but exposure to
light destroys riboflavin
• Heat stable
Flavin adenine
dinucleotide = FAD
Riboflavin = ring
+ ribitol
isoalloxazine
ring
ribitol
Niacin (B3)
• Energy metabolism
• Disease – pellagra – The Four D’s
– Dermatitis
– Diarrhea
– Dementia
– Death
23
Niacin (= vitamin B3)
Nicotinic acid, Nicotinamed, Niacinoamide
- is a precursor to NAD+/NADH and NADP+/NADPH, which play
essential metabolic roles in living cells.
- Participates in over 200 reactions
- Niacin is also involved in both DNA repair, and the production
of steroid hormones in the adrenal gland.
- Heat stable
Pantothenate (= vitamin B5) is required to synthesize coenzyme-A and to synthesize
and metabolize proteins, carbohydrates and fats
•CoA is formed when pantothenic acid combines with ADP and part of
cysteine
•“Pantos” means everywhere
•deficiency is very rare
•deficiency symptoms: irritability, fatigue, and apathy also impaired
acetylcholine synthesis leads to neurological symptoms (numbness and
muscle cramps)
Vitamin B5
• sources: meats, mushrooms, eggs, whole
grains, legumes, broccoli and avocados, liver
• AI 5mg/day
• Deficiency is rare: “Burning foot syndrome”
-skin sensations exacerbated by warmth
• Alcoholics at risk
Vitamin B6
•
1934- cured dermatitis in rats
PLP
B6 - Pyridoxamine
• Neurotransmitter, co-enzyme in over 100 reactions
• Deficiency surfaced in 1951 in infants from
overprocessed infant formula
- heat treatment caused pyridoxyl-lysine
- seizures, convulsions
• Transamination, decarboxylation, heme synthesis,
CHO metabolism, lipid metabolism, neurotransmitter
synthesis
• conversion of tryptophan to niacin, tryptophan to
serotonin, tyrosine to dopamine
28
Sources
• Meat, fish, poultry, banana, spinach, avocado,
potato
• Heat and alkaline sensitive
• RDA 1.3-1.7 mg/day
• Alcohol reduces PLP formation
Biotin (= vitamin B7) is a coenzyme in metabolism of fatty acids and leucine as
well as with pyruvate carboxylase in gluconeogenesis
•Allows 3 essential aa to be oxidized for energy (isoleucine, threonine,
methionine)
•deficiency can be caused by the excessive consumption of raw egg
whites (20 eggs/day would be required to induce it), which contain high
levels of the protein avidin, which binds biotin strongly. Avidin
denaturates upon heating (cooking), while the biotin remains intact.
•sources: (AI=30 ug/day) egg yolk, liver, bananas, cauliflower and
carrots are particularly high in biotin
B7
– deficiency is relatively rare and mild, and can
be addressed with supplementation.
– Deficiency causes skin disease and hair loss
31
Folate
• Folic acid, folate, folacin
• Contains a Pteridine group, paraaminobenzoic acid (PABA), glutamic acid
• Coenzyme form is: Tetrahydrofolic acid (THFA)
and tetrahydrofolate (THF)
Folate function
• DNA synthesis
-transfer of single carbon units
-synthesis of adenine and guanine
• Amino Acid metabolism
-neurotranmitter formation
-homocysteine metabolism
Sources
•
•
•
•
•
RDA 400 ug/day for adults
Liver
Grains, legumes
Leafy green vetabols
Susceptible to heat, oxidation, UV
Deficiencies
• Megaloblastic anemia
• Neural tube defects (spina bifida,
anencephaly)
• Elevated risk of heart disease (high
homocysteine levels)
Cobalamin (= vitamin B12) normally involved in the
metabolism of every cell of the body, especially affecting the
DNA synthesis and regulation but also fatty acid synthesis
and energy production.
•deficiency symptoms: Low levels of B12 can cause a range of
symptoms including fatigue, shortness of breath, diarrhea, nervousness,
numbness, or tingling sensation in the fingers and toes. Severe
deficiency of B12 causes neurological damage and pernicious anemia.
•sources: good dietary sources include fish, shell fish, dairy products,
organ meats (particularly liver and kidney), eggs, beef, and pork
B12 –
Development of red blood cells
Lack of it makes one anemic
Hard for vegans to get
• Gastric bypass surgery – causes deficiency
Vitamins and Metabolism
Catabolism of Glucose
Catabolism of Fatty acids
Catabolism of Amino Acids
Metabolic
pathways
involving B
Vitamins