MEDI213 Lecture Notes - Lecture 10: Wernicke–Korsakoff Syndrome, B Vitamins, Thiaminase
7 Aug 2018
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B Vitamins
Describe the features of a water-soluble vitamin
Discuss the functions of the water-soluble vitamins
Describe daily requirements and food sources of the water-soluble vitamins
Discuss the signs of vitamin deficiency and excess
What is a vitamin
• Essential organic substance needed in very small amounts
• Support metabolism, growth and maintenance of body cells (not a source of energy)
• Water soluble or fat soluble
Water soluble vitamins
• Includes B and C vitamins
• Only small amounts store within body
• Excess excreted via kidneys (urine), therefore risk for toxicity low (except niacin, B6,
vit C)
• B12 can be stored in liver
• More susceptivle to destruction during cooking and storage of foods
o Heat
o Light
o pH >8
o Air
o Leaching into cooking water
B Vitamins as Coenzymes
• B vitamins occur in food in co enzyme form
o Combine with inactive enzymes
o Facilitate metabolism and many cellular reactions
• Examples:
o CoA, TPP, NAD, NADP, THFA
• B vitamins in coenzyme form; bound by proteins
• Digestive processes in stomach and small intestine release them for absorption
• 50-90% free B vitamins absorbed
• Once inside cells, coenzyme form resynthesised
• Absorbed in small intestine (jejenum and ileum)
Grains
• Valuable source of B vitamins
• Bran and husk removed in milling → loss of some vitamins and minerals
• Wholegrains recommended
THAMIN (B1)
• Not heat stable
• Destroyed by alkaline conditions
• Destroyed by sulphite and thiaminase (in raw fish)
• Structure: contains pyrimidine ring and thiazolium ring
• Central C bond susceptible to heat, alkaline conditions
• Absorption
o Absorbed in small intestine
▪ In higher concentrations by passive absorption
▪ Lower levels require active transport
o Reduced by presence of tannins
o Primarily in body in coenzymes form TPP, usually transported by RBCs
o Rarely stored in body (small amount in liver and muscles)
o Excess excreted at kidneys
• Function
o Important coenzyme in CHO metabolism
o Coenzyme for catabolism of brained chain amino acids (valine, leucine,
isoleucine)
• Requirements
o UL unable to be established
o Toxicity unlikely from food sources
o
• Deficiency
o Beri Beri (dry – no odema), wet – (oedema)
▪ Reduced CHO and protein metabolism
▪ Affects cardiovascular, nervous, muscular and gastrointestinal
systems
▪ Symptoms = weakness, fatigue, nerve degeneration, tingling, poor
coordination, muscular pain, psychological disturbances, headache
▪ Symptoms can appear 10 days after low thiamine diet
o Wernicke Korsakoff Syndrome
▪ Found in alcoholism
• Alcohl needs thiamine for metabolism
• Absorption of thiamine reduced
• Poor quality diet
▪ Symptoms:
• Involuntary eye movement, paralysis of eye muscle,
staggering, confusion
o Two deficiencies not normally seen together
• Food sources
o Bread making flour fortified
o Toxicity not usually a problem
o
RIBOFLAVIN (B2)
• Very unstable – most lost 4 hours exposure to light
• Absorption
o Released from bound form by HCl in stomach
o Absorbed in jejenum
o Bioavailability ~95% of that consumed
o Transported by protein carriers in blood
o Mostly converted back to coenzyme form in SI, heart liver and kidneys
o Excess excreted via kidneys
• Functions
o Coenzyme for metabolidm of proteins and fats
o Energy production (aerobic pathway for glucose metabolism)
o Immune function
o Nervous system
o Conversion of tryptophan to niacin, and folate metabolism
o Conversion of pyridoxine (B^) to active form
• Requirements
o UL not established
o Toxicity unlikely from food
o
• Deficiency
o Ariboflavinosis
o Inflammation of tongue (glossitis) and mouth (stomatitis), cracking around
corners of mouth (cheilosis), seborrheic dermatitis, fatifue, confusion,
anaemia, headache
• Food sources
o DAIRY
o Meat, eggs, mushroom, spinach/leafy graans, fortified foods (e.g. cereal)
Document Summary
What is a vitamin: essential organic substance needed in very small amounts, support metabolism, growth and maintenance of body cells (not a source of energy, water soluble or fat soluble. Grains: valuable source of b vitamins, bran and husk removed in milling loss of some vitamins and minerals, wholegrains recommended. Thamin (b1: not heat stable, destroyed by alkaline conditions, destroyed by sulphite and thiaminase (in raw fish, structure: contains pyrimidine ring and thiazolium ring, central c bond susceptible to heat, alkaline conditions, absorption, absorbed in small intestine. Involuntary eye movement, paralysis of eye muscle, staggering, confusion: two deficiencies not normally seen together, food sources, bread making flour fortified, toxicity not usually a problem. Immune function: nervous system, conversion of tryptophan to niacin, and folate metabolism, conversion of pyridoxine (b^) to active form, requirements, ul not established, toxicity unlikely from food, deficiency, ariboflavinosis.
