b-vitamins working individually and in concert 1
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B-VITAMINSWorking 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-CoAParticipates 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 AcidPart 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 B6Three forms
Pyridoxal, pyridoxine, and pyridoxamineAll 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 functionStored extensively in muscle tissue
Large doses do not enhance muscle performance!
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Vitamin B6Deficiency
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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FolateKnown as folacin or folic acidPrimary coenzyme form – THF (tetrahydrofolate)Transfers single-carbon compounds during metabolism (methlyation)Converts vitamin B12 to coenzyme form
Involved in DNA synthesisNeeded for cell division
Helps process amino acid homocysteine
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FolateFolate 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 activationVery 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 B12Digestion 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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CholineManufactured 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 fetusCommon sources: milk, eggs, peanutsDeficiencies are rare
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B-Vitamins In ConcertEach 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 Concert30