Water Soluble Vitamins

B Vitamins

• Do not provide energy directly
• Help the body metabolize the nutrients that yield energy (carbohydrates, fat, protein)
• Some B vitamins are components of coenzymes
• B vitamins include: thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin B₆, folate, vitamin B₁₂

Thiamin (vitamin B₁)

• Absorbed in jejunum by a carrier-mediated system and passive diffusion
• Transported in the blood and by red blood cells
• Part of coenzyme thiamin pyrophosphate (TPP) used in energy metabolism of
  • Carbohydrates (conversion of pyruvate into acetyl CoA between glycolysis and Krebs cycle)
  • Branched-chain amino acids (conversion of alpha-ketogluterate into succinyla-CoA in the Krebs cycle)
• Thiamin deficiencies: Beriberi and Wernicke-Korsakoff Syndrome
  • Beriberi
    • 1897, Dr. Christiaan Eijkmann, Indonesian island of Java
    • Natives suffering from beri beri
    • Symptoms included muscle weakness, weight loss, nervous disorders and ultimately paralysis and death
    • Dr. Eijkmann noticed chickens exhibiting some of the same symptoms as the beri beri victims
    • Natives (victims) ate white rice while (healthy) chickens were fed brown rice but chickens with similar symptoms to natives were fed white rice
    • Conclusion: something on the brown coat of rice prevented beri beri
    • Types:
      • Dry beriberi – peripheral neuropathy, “burning feet syndrome”, abnormal reflexes, and diminished sensation and weeknedss in the legs
      • Wet beriberi – cardiac manifestations such as rapid heart rate, enlargement of the heart, edema, difficulty breathing, and congestive heart failure
      • Cerebral beriberi – Wernicke-Korsakoff syndrome
  • Wernicke-Korsakoff Syndrome
    • Result of habitual use of alcohol
    • Wernicke’s disease – damage to multiple nerves in the central and peripheral nervous system
    • Korsakoff syndrome – impairment of memory and intellect/cognitive skills; confabulation (fabrication) occurs to make up for gaps in memory
  • Other factors causing thiamine deficiency:
    • Hemodialysis, diuretics, alcoholism – increases flow of urine and loss of thiamin
    • Anti-thiamin factors – chemicals found in plants that bind to and/or react with thiamin to render it in a form oxidized in the body; tea and coffee may cause thiamin depletion
    • Thiaminase – enzyme found in raw shellfish and raw freshwater fish; enzyme breaks down thiamin in food
• Dietary sources: whole-grain, fortified, or enriched grain products, pork, soy milk, ham, and bacon
• RDA: men 1.2 mg/day and women 1.1 mg/day
• Toxicity: none reported but anaphylactic shock can occur in dosages lager than 3 grams

Riboflavin (vitamin B₂)

• In stomach, HCl releases riboflavin from its bound from
• Absorbed actively or passively
• Transported in the blood via protein carriers
• Part of coenzyme Flavin mononucleotide (FMN) and Flavin adenine dinucleotide (FAD) used in energy metabolism
• High amounts excreted turn urine the bright yellow color
• Riboflavin deficiencies: ariboflavinosis
  • Cracks at the corners of the mouth (cheilosis), painful, redness tongue (glossitis), skin rash, photophobia (sensitivity to light).
• Dietary sources: milk products, fried beef liver, steamed oysters, enriched or whole grains
• RDA: men 1.3 mg/day and women 1.1 mg/day
• Toxicity: none reported

Niacin (nicotinic acid, nicotinamide, niacinamide, B₃)

• Readily absorbed in the stomach and intestine by active and passive transport
• Transported to liver to be converted to coenzyme forms, NAD and NADP
• Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine diculeotide phosphate (NADP) used in energy metabolism
• Niacin Deficiencies: Pellagra also “smooth swollen red tongue”
  • Pellagra – associated with consumption of unfortified maize (corn) as a dietary staple
  • Diets were low in the amino acid tryptophan, precursor of niacin and/or endogenous niacin was bound and non-bioavailable
  • Flour now is enriched with niacin
  • Cultures still relying on maize as a staple presoak maize in alkaline lime prior to cooking to liberate bound niacin
• Dietary sources: milk, eggs, meat, poultry, fish, whole grain and enriched breads and cereals, nuts
• RDA: men 16 mg/day and women 14 mg/day
• Toxicity:
  • Only observed in individuals who use supplements
  • Supermegadose levels of nicotinic acid (2000 to 4000 mg) as an adjunct to tryptophan treatment of depression or to lower blood cholesterol and raise HDL's, some patients report “niacin flush” (red skin), itching skin (urticaria), heartburn, nausea, etc.

Pantothenic Acid

• Part of coenzyme A (CoA) which is used in metabolism of carbohydrate, protein, alcohol, and fat
• Pantothenic acid deficiencies: none reported
• Dietary sources: organ meats, mushrooms, broccoli, avocados, whole grains, sunflower seeds, peanuts
• Adequate Intake (AI): 5 mg/day
• Toxicity: none reported

Biotin

• Found in two forms: free vitamin and the protein bound coenzyme form (boicytin)
• Cofactor of four carboxylase enzymes (which add CO₂ to a substance) used in fat synthesis, amino acid metabolism, and glycogen synthesis
• Biotin deficiencies: biotinidase in small intestine cleaves the bond between biotin and a protein, releasing the free biotin vitamin – if infants lack the enzyme then levels of free biotin vitamin decrease; may lead to skin rash, hair loss, convulsions, impaired growth
• Dietary sources: widespread in foods; organ meats, egg yolks, soybeans, fish, whole grains
• Adequate Intake (AI): 30 ug/day
• Toxicity: none reported

Vitamin B₆

• Three forms (pyridoxine, pyridoxal, pyridoxamine) – all converted into the coenzyme PLP (pyridoxal phosphate)
• PLP involved in more than 100 enzymatic reactions
  • Functions as a decarboxylase, an enzyme removing carbon dioxide from amino acids
  • Catalyzes the first step in synthesis of heme in red blood cells
  • Part of an enzyme that release glucose from glycogen during glycogenolysis
  • Catalyzes fatty acid synthesis
  • Catalyzes synthesis of neurotransmitters (serotonin, dopamine, norepinephrine, histamine, and GABA)
  • Converts the amino acid tryptophan into the B vitamin niacin
• Vitamin B₆ deficiencies: seborrheic dermatitis, microcytic hypochromic anemia, convulsion, depression, and confusion
• Dietary sources: meats, fish, poultry, potato, liver, soy products
• RDA: 1.3 mg/day
• Toxicity: nerve damage, depression, fatigue, headaches

Folate

• Consists of three parts: pteridine, PABA, and one or more glutamates – the chemical compound is collectively called pteroglutamic acid (PGA)
• Polyglutamate forms are hydrolyzed to the monoglutamate form and actively absorbed in the intestines
• In body target cells, all forms of folate are converted into the coenzyme form, called tetrahydrofolic acid (THFA or THF)
• THFA involved in the synthesis of thymidylate (a component of DNA) and the synthesis of DNA bases’ adenine and guanine
• Folate deficiencies: megoblastic anemia, smooth red tongue, mental confusion, weakness, fatigue, headache, elevated homocysteine levels (which may increase risk of blood vessel injury and thus heart attack)
• Dietary sources: fortified grains, asparagus, lentils, orange juice, leafy green vegetables, legumes, seeds, liver
• RDA: 400 ug/day
• Toxicity: may mask vitamin B₁₂ deficiency symptoms

Vitamin B₁₂

• Also called cobalamin
• Free vitamin (cyanocobalamin) and two active coenzymes (methylcobalamin and 5-deoxyadenosylcobalamin)
• Contains the mineral cobalt and is synthesized exclusively by bacteria, fungi, and algae
• B₁₂ in food is released from proteins by action of HCL and pepsin in gastric juice
• The free B₁₂ binds to a protein (R-protein) and travels to the small intestines where a protease cleaves the protein from the vitamin
• Free B₁₂ then is bound to an intrinsic factor and travels to the ileum where B₁₂ is absorbed
• 50% of B₁₂ absorbed in healthy adult
• Disruption of absorption can occur as a result of
  • Absence or defective synthesis of R-protein
  • Defective binding of intrinsic factor/B₁₂ complex to cells of ileum
  • Absence of much of the ileum and stomach
  • Absence or defective synthesis of the intrinsic factor
  • Bacterial overgrowth of the small intestines
  • Use of anti-ulcer medications
  • Chronic mal-absorption syndromes
• B₁₂ deficiencies: achlorhydria and/or atrophic gastritis causes stomach cells to be damaged and impairs the production of HCL and intrinsic factor – without HCL and the intrinsic factor, B₁₂ cannot be absorbed and may lead to pernicious anemia
• Dietary sources: meat, poultry, seafood, eggs, milk, and fortified cereals
• RDA: 2.4 ug/day
• Toxicity: none reported

Vitamin C (ascorbic acid)

• Found in all living tissues
• Most animals (except humans and other primates) can be synthesize it from glucose
• Absorption occurs in the small intestine by active and passive transport
• 70-90% is absorbed at daily intakes between 30-180 mg – 50% or less at higher dosages
• Acts as a reducing agent
• Functions as an antioxidant
• Involved in connective tissue biosynthesis
• Aids in the absorption of forms of iron
• Protects white blood cells against oxidative damage
• Vitamin C deficiencies: Scurvy, fatigue, pinpoint hemorrhages, bleeding gums and joints, impaired wound healing, bone pain, fractures, and diarrhea
• Dietary sources: orange juice and other citrus fruits, brussels sprouts, bell peppers, broccoli, tomatoes, potatoes, papaya, strawberries
• RDA: men 90 mg/day and women 75 mg/day
• Toxicity: nausea, abdominal cramps, diarrhea, fatigue, headache

Vitamin-like Compounds

Choline

• Absorbed in the small intestines
• Found in all tissues
• Precursor of acetylcholine (a neurotransmitter) and phosphatidylcholine (lecithin)
• Choline deficiencies: liver damage
• Dietary sources: milk, liver, eggs, peanuts
• Adequate Intake (AI): men 550 mg/day and women 425 mg/day
• Toxicity: body odor, low blood pressure, reduced growth rate, liver damage

Others...

• Carnitine - involved in transport of fatty acids and is considered an antioxidant
• Inositol - involved in second messenger systems (i.e. hormone function)
• Taurine - major component of bile
• Lipoic Acid - cofactor of many enzymes (e.g., pyruvate dehydrogenase) and function as an antioxidant