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