B-Vitamins

1. B-Vitamins Working individually and in concert

2. 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

3. Function of a Coenzyme

5. 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

6. 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

7. Food Sources of Thiamin

8. 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

9. Food Sources of Riboflavin

10. 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

11. 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

12. Food Sources of Niacin Niacin is tolerant to heat but can be lost in cooking water

13. 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

14. 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

15. 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!

16. 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

17. Food Sources of B6

18. 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

20. 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)

21. 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

22. 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

23. Food Sources of Folate

24. 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

25. 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

26. 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

27. Anemia of B12 or Folate Deficiency

28. 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

29. 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

30. B-Vitamins in Concert