Transcript B-Vitamins
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B-VITAMINS
Working individually and in concert
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Relationship with Energy Metabolism
• Vitamins do not provide the body with fuel for energy
• However, they can work as coenzymes
• Assist enzymes with release of energy
• Without coenzyme, an enzyme cannot function
• B-vitamins assist enzymes that unlock energy from our energy-
yielding nutrients
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Function of a Coenzyme
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Thiamin
• Part of coenzyme thiamin pyrophosphate (TPP)
• Energy metabolism
• Conversion of pyruvate to acetyl CoA in glucose metabolism
• Participates in citric acid cycle in mitochondria
• Essential for nerve activity and muscle activity
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Thiamin
• Deficiency
– Malnourished and alcoholics
– Beriberi
• Dry – nervous system
• Wet – cardiovascular system
• Toxicity
– No adverse effects
• No UL
• Prolonged cooking destroys thiamin
• Leaches into water when boiling or blanching foods
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Food Sources of Thiamin
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Riboflavin
• Serves as coenzyme in energy metabolism
– Flavin mononucleotide (FMN)
– Flavin adenine dinucleotide (FAD)
• Carries hydrogen atoms and their electrons to electron transport chain
• Each time it does this, 2 molecules of ATP are generated
• Deficiency
– Inflammation of membranes
• Toxicity
– No UL
• Destruction of riboflavin
– Ultraviolet light (thus the opaque containers for milk)
– Irradiation
– Not destroyed by cooking
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Food Sources of Riboflavin
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Niacin
• Two chemical structures
• Nicotinic acid
• Nicotinamide
• Major form of niacin in blood
• Two coenzyme forms participate in metabolic reactions
• Nicotinamide adenine dinucleotide (NAD)
• Carries hydrogen atoms and their electrons to electron transport chain
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Niacin
• Deficiency
• Pellagra
• Symptoms: 3 Ds
• Diarrhea
• Dermatitis
• Dementia
Toxicity
Naturally occurring:
no harm
Supplements or drugs
“Niacin flush”
Nausea, vomiting, liver damage, glucose intolerance
Potential health benefits of large doses of nicotinic acid: may
lower LDL cholesterol
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Food Sources of Niacin
Niacin is tolerant to heat but can be lost in cooking water
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Biotin
Coenzyme critical in citric acid cycle
Facilitates first step in cycle (entry point for acetyl-CoA
Participates in breakdown of fatty acids and amino
acids
Participates in gluconeogenesis and fatty
acid synthesis
Deficiency is very rare, no known toxicity
Widely distributed in foods, needed in small amounts
(30 mcg/day)
Raw egg white consumption
Deficiency symptoms: hair loss, rash, neurological
impairment
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Pantothenic Acid
Part of chemical structure of coenzyme A
Entry point into many metabolic pathways
Involved in >100 different steps in synthesis of lipids,
hormones, neurotransmitters, and hemoglobin
Deficiency
is rare, no known toxicity
Symptoms: failure of all body systems, fatigue, GI distress,
neurological disturbances
Food sources
Widely available in meats, whole grains, potatoes, egg yolks,
broccoli
Easily destroyed in food processing: freezing, canning, refining
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Vitamin B6
Three forms
Pyridoxal, pyridoxine, and pyridoxamine
All converted to coenzyme pyridoxal phosphate
(PLP)
Amino acid metabolism
Urea metabolism
Conversion of tryptophan to niacin or serotonin
Synthesis of heme, nucleic acids, & lecithin
Influences cognitive performance, hormone activity,
and immune function
Stored extensively in muscle tissue
Large doses do not enhance muscle performance!
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Vitamin B6
Deficiency
Impacts amino acid metabolism
Abnormal compounds made from tryptophan accumulate in
brain
Early signs: depression, confusion
Advanced symptoms: abnormal brain wave patterns,
convulsions
Alcohol: increases breakdown and excretion of PLP
Isoniazid (anti-tuberculosis med): B6 antagonist
Toxicity: only from supplements
Can cause irreversible nerve degeneration
In food
Small amounts in lots of foods
Lost when food is heated
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Food Sources of B6
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Folate
Known as folacin or folic acid
Primary coenzyme form – THF
(tetrahydrofolate)
Transfers single-carbon compounds
during metabolism (methlyation)
Converts vitamin B12 to coenzyme form
Involved in DNA synthesis
Needed for cell division
Helps process amino acid homocysteine
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Folate
Folate disposal from body
Secretion by liver into bile
Can be recycled via enterohepatic circulation
Vulnerable to GI tract injuries
Depletion occurs rapidly with alcohol abuse
Leads to greater tissue damage, greater losses (and
impaired absorption of other nutrients, too)
Bioavailability
Synthetic form (folic acid) 1.7x more bioavailable than
natural form (folate)
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Folate Status and Birth Defects
• Needs rise during pregnancy
• Closure of neural tube, from which brain and spinal cord
develop, occurs during first few weeks
• Low folate status in mother can cause brain and spinal cord
disorders, and even death of infant/fetus
• Rate of neural tube defects has declined since folate
fortification began in 1996
• Adequate folate status may also prevent cleft lip or palate
• Supplementation or careful monitoring of dietary
folate adequacy recommended for all women of
childbearing age
• To get 400 mcg/d, at least 5 servings of fruits and vegetables
recommended
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Folate
Deficiency
Impairs cell division and
protein synthesis
Red blood cells and GI tract
cells falter
Anemia
GI tract deterioration
Primary deficiencies: due to
inadequate intake or
increased need
Secondary deficiencies: drugs
Anti-cancer meds (folate
antagonists)
Heavy use of aspirin or
antacids
Oral contraceptives
Smoking
Toxicity
Can occur from natural or
supplemental/fortified sources
Primary concern: can mask B12
deficiency, since early signs of
B12 deficiency are usually due
to impaired folate activity
Food sources
Heat and oxidation destroy
folate
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Food Sources of Folate
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Vitamin B12
Vitamin B12 and folate depend on each
other for activation
Very important for DNA synthesis, cell
replication
Individual roles of vitamin B12
Maintains myelin sheath, promotes normal
growth of nerve cells
Involved in bone cell metabolism/activity
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Vitamin B12
Digestion and absorption
Stomach
HCl acid and proteases release B12 from dietary protein
Secretes intrinsic factor
Small intestine
Intrinsic factor binds to B12, absorbed as complex
Enterohepatic pathway continuously recycles
B12
In healthy individuals, deficiency is rare, since it is
constantly reabsorbed
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Vitamin B12
Deficiency
Inadequate absorption or intake
Lack of hydrochloric acid or intrinsic factor
Lack of animal foods
Individuals at risk
Older adults: atrophic gastritis
Vegans
Those with anemia of folate deficiency
Symptoms of vitamin B12 deficiency
Moderate: cognitive impairment
Severe: creeping paralysis
Toxicity unknown
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Anemia of B12 or Folate Deficiency
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Choline
Manufactured from amino acid methionine in body
When insufficient in diet, body alone cannot meet
needs
Used to make neurotransmitter acetylcholine
Supports neural tube closure and nervous system
development in fetus
Common sources: milk, eggs, peanuts
Deficiencies are rare
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B-Vitamins In Concert
Each B-vitamin coenzyme is involved in energy
metabolism
Some vitamins are necessary to activate others
B12 and folate
Riboflavin and B6
Riboflavin, B6, and Niacin (synthesis from tryptophan)
Deficiencies
Single B-vitamin deficiencies seldom show up in
isolation
Frank deficiency is rare in US, but suboptimal intake
is more common
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B-Vitamins in Concert