Water Soluble Vitamins Flashcards
7 POSSIBLE RISKS FOR DEFICIENCY
- Is the dietary INTAKE adequate /sufficient?
- Is the nutrient AVAILABLE for absorption? (i.e. is digestion of food optimal?)
- Is ABSORPTION optimal?
- Is CONVERSION to the biologically active form optimal?
- Is the nutrient AVAILABLE to the cells? (i.e. are transport proteins available to
take it to the cells) - Is EXCRETION increased?
- Are there any reason for INCREASED REQUIREMENTS?
list all water soluble vitamins
Vitamins of “B complex” group: – B1: thiamin – B2: riboflavin – B3: niacin – B5: pantothenic acid – B6: pyridoxine – B7: biotin – B9: folate – B12: cobalamin • Choline • Vitamin C: ascorbic acid
list all water soluble vitamins and their coenzyme
Vitamins of “B complex” group: – B1: thiamin TTP – B2: riboflavin FAD FMN – B3: niacin NAD NADP – B5: pantothenic acid CoA – B6: pyridoxine PLP – B7: biotin biotin – B9: folate THFA – B12: cobalamin 5deoxycobalamine • Choline choline • Vitamin C: ascorbic acid
Thiamine is required for what reaction?
Required for decarboxylation reactions: removal of a COOH groups, and release of 1 molecule of carbon dioxide in the process. - Required in the “link reaction” where pyruvate is converted to acetyl CoA; and in the CAC
antagonist of thiamine and food sources
Mandatory fortification in bread-making flour • Found in a wide variety of foods, but some foods contain thiamin antagonists, which lower its bioavailability: - Raw fish, shellfish: contain thiaminase, an enzyme that destroys thiamin - Brussel sprouts, and beets contain compounds that oxidise thiamin
Deficiency thiamine
Deficiency 1- Beriberi •
2- Wernicke-Korsakoff syndrome: cerebral beriberi in alcoholism. •
RIboflavin digestion absorption transport
Digestion-Absorption
• HCl in stomach releases riboflavin bound to dietary compounds
• Free riboflavin absorbed via active transport or diffusion depending on
concentration. Only 60-65% of intake is absorbed
Transport
• Transported by protein carriers in the blood
• Converted to the coenzyme forms (FAD or FMN) in most tissues
Storage
• Small amount stored in liver, kidneys, heart
Excretion
• Excess excreted in urine: will cause bright yellow urine when taken as supplement
RIboflavin 6 functions
Key roles in energy metabolism in the CAC + ETC: FAD and FMN shuttle hydrogen
atoms into the electron transport chain
2. FAD required in the CAC (as per below)
3. In beta-oxidation: conversion of fatty acids to acetyl CoA requires fatty-acyl
dehydrogenase, which requires FAD
4. The reduction of glutathione (part of endogenous non-enzymatic antioxidant
system) requires the activity of an FAD-dependent enzyme: glutathione reductase
5. The formation of niacin (vitamin B3) from tryptophan (amino acid) requires FAD
6. Formation of the vitamin B6 coenzyme form (PLP) requires FMN
Deficiency
Affects mouth, skin, red blood cells
• Signs/symptoms: glossitis, angular stomatitis (pictures), scaly
skin, anemia, fatigue, headaches
• RBC riboflavin and glutathione reductase concentrations
indicate riboflavin status (biomarker)
• Increased risk: chronic alcoholism, malabsorption
syndromes, use of contraceptive pill, high stress, elderlies
Food sources of riboflavin
bundant in dairy milk products • In small amount in mushrooms, green leafy vegetables, broccoli, and asparagus • Present in enriched white bread, crackers, eggs, meat, and liver • Exposure to light causes rapid breakdown: - Opaque paper and plastic containers should be used to package riboflavinrich foods (e.g. milk)
Absorption transport storage niacin
Digestion-Absorption
• Niacin bioavailability is low in grain, especially corn: tightly bound to protein; less than
30% can be absorbed.
Soaking corn in lime water [calcium hydroxide in water to increase alkalinity] can
improve bioavailability. This method is used where corn is a staple food
• Some absorption occurs in stomach, but mainly in small intestine: active transport
and passive diffusion depending on concentration available
• Endogenous synthesis can occur with tryptophan as precursor
Transport and activation
• Converted to coenzymes form in all tissues: NAD+ and NADP+
Storage
• Limited storage in liver
Excretion
• Excess excreted in urine
Functions of naicin
Required in over 200 reactions of cellular metabolism 2. Required in oxidation-reduction reactions as NAD+ and NADP+ 3. Catabolism of carbohydrate (pyruvate => lactate pathway), fat, and protein 4. NAD+ : Electron acceptor in glycolysis and in the CAC 5. In gluconeogenesis: required to produce oxaloacetate 6. Alcohol dehydrogenase” removes hydrogen => NAD is the electron acceptor 7. NADPH+H+ : Important co-enzyme in lipogenesis
deficiency in niacin
Deficiency • Pellagra: pelle “skin”; agra “rough” (in Italian) • Widespread effects given the widespread functions of niacin -Dermatitis, diarrhea, dementia, death (if not treated): “the 4D’s” -Red rash on skin exposed to sunlight
Niacin sources
Niacin can be endogenously synthesised from
dietary tryptophan (not an efficient process
however + tryptophan is an EAA => needed
elsewhere)
• 60 mg tryptophan = 1 mg niacin
• 1 g of protein = 10 mg tryptophan
• The RDI is therefore expressed as niacin
equivalents, i.e. it includes the niacin that can
be made endogenously from dietary
tryptophan
• Note: certain cereals (sorghum) contain niacin
synthesis inhibitors
Main dietry sources : chicken , tuna , salmon, peanut butter , almomds , fortified rice bread ceral
Pathoic acid functions
. Essential as coenzyme A for the formation of
acetyl CoA in all energy production
pathways (entry into the CAC)
2. Acetyl CoA is the building block in the
synthesis of cholesterol, fatty acids, steroid
hormones, bile acids
3. Pantothenic acid is part of acyl-carrier
proteins; shuttle fatty acids through the
pathway of fatty acid elongation: adding of
carbon atoms in lipogenesis
pantothoaic acid deficiency
Deficiency is rare because found in a large variety of foods
Symptoms of deficiency may include: headaches, burning feet fatigue, impaired
muscle coordination, GIT disturbances
DIgestion, absorption TRANSPORT, STORAGE AND EXCRETION OF PYRIDOXINE
Digestion-Absorption
• Present in food in the coenzyme form pyridoxal phosphate (PLP). Converted to
B6 for absorption. The animal source form is more readily absorbed (availability?)
• Passive diffusion in small intestine
• Can also be absorption in the coenzyme form if a lot is available
Transport
• Portal vein to the liver
• Active form PLP made in the liver, circulates bound to albumin to tissues
Storage
• Muscle tissue is main storage site
Excretion
• Excess excreted in urine
Pyridoxine functions
1- PLP is necessary for over 100 enzymatic
reactions, especially involving nitrogen
groups
2- PLP required in almost all amino acids
metabolism: required in amino acid
transamination for synthesis of non-essential
amino acids
3- Required in glycogenolysis: maintaining
blood glucose levels during short-term fasting
4- Required in the synthesis of key metabolic
compounds:
- Haeme ring
- Histamine
- Neurotransmitters: serotonin (from
tryptophan), dopamine and adrenaline
(from tyrosine), and GABA (from glutamic
acid)
- Production of niacin from tryptophan
5- Gene expression regulation
6- Modulation of effects of steroid hormones
7- Involved in immune function regulation
Pyridoxine deficiency
Deficiency • Oily dermatitis • Microcytic hypochromic anemia (small and pale RBC: due to reduced haeme and haemoglobin synthesis) • Convulsions, depression, confusion (due to altered neurotransmitters synthesis) • Individuals at risk of deficiency - Very poor diet, malabsorption issues - Chronic alcoholism: increased acetaldehyde from alcohol metabolism blocks the formation of PLP in the liver
pyridoxine toxcicity
Toxicity: Risk of permanent nerve damage (walking difficulties, peripheral neuropathy) • Caution when using multiple supplements daily: B6 is found in hair/nail, anti-PMS, multivitamins, sports and body-building specific supplements
pyridoxine sources
pinto beans pistachious oatmeal although plant sources less readily absorbed \ tuna turkey nuggets beef
Biotin ABSORPTION, TRANSPORT, STORAGE AND EXCRETION
Digestion-Absorption
• Found in food as free biotin or biocytin: bound to the AA lysine in protein
• Biotinidase unbinds biotin for absorption
• Free biotin absorbed by active transport (sodium dependent carrier)
• Bioavailability greater in eggs and meat sources
• Some minor microbial production in large intestine
• Generally biologically active as biotin (this is an exception to the coenzyme rule)
Storage
• Minimally stored in liver, muscle, brain
Excretion
• Excretion mainly via urine, some in bile
functions of biotin
Required in carboxylation reactions: coenzyme of carboxylase enzymes:
carboxylation of acetyl-CoA to form malonyl CoA at the start of lipogenesis
2. Required for metabolism of carbohydrates, fats and proteins, and formation of
CAC intermediates
3. Catabolism of branched-chain amino acids: ketogenic BCAA to make acetyl-CoA
4. Involved in DNA folding in the nucleus: biotin binds to histone that facilitate DNA
folding => gene stability
5. Involved in the production of oxaloacetate from pyruvate
biotin deficiency
Deficiency
• Skin rash, patchy hair loss, convulsions, impaired
growth after birth
May be due to:
• Biotinidase enzyme deficiency (genetic polymorphism)
• Excessive consumption of raw egg-white (>12 per
day). Contains avidin: a glycoprotein with high specific
affinity for biotin. Inhibits biotin absorption in the small
intestine. Cooking egg-white denatures avidin
sources biotin
chicken liver
peanuts
salmon
Folate vs follic acid
Folate in natural food contains 3 components:
- Pteridine ring, para-aminobenzoic acid (PABA) and
1 or more glutamates or glutamic acids E.g. 1
glutamate = folate monoglutamate
• 90% of food folate contain 3 or more glutamates
= polyglutamate
• Folic acid = synthetic source of folate: used in fortified foods
and supplements
- Pteroic acid + 1glutamate
- More stable than folate
- Presents in the right form for optimal absorption
=> 100% bioavailable on empty stomach
ABSORPTION, TRANSPORT, STORAGE AND EXCRETION OF FOLATE
Digestion-Absorption
• Food processing destroys 50-90% of folate (heat, oxidation, light)
• Polyglutamates must be broken down in the GIT to monoglutamates by folate
conjugase for absorption (zinc dependent)
• Folate monoglutamate: absorbed by active transport in small intestine
• Folic acid (supplements and in fortified food): passive diffusion
• Coenzyme = tetrahydrofolate / tetrahydrofolic acid (= THF / THFA)
Activation
Conversion to coenzyme occurs in the enterocytes for folate and in the liver for folic
acid by dihydrofolate reductase
Transport
• Circulates in many forms: the main form is 5-methyl THFA (5 Me-THFA)
• Converted back to polyglutamates in cells (traps folate inside cells)
Storage: significant amount stored in the liver (about 500–20,000 µg, equal to several
months supply) = > an exception for water soluble vitamins
Excretion via urine and feaces
Folate functions
Central role as coenzyme THFA: cell division, proliferation, and maintenance of new cells
- DNA synthesis and repair:
- Addition of methylene group (CH2) by THFA to nucleotide uracil to become thymine
- Synthesis of adenine and guanine - Formation of serotonin, adrenaline, dopamine
- Amino acid metabolism: in transamination by accepting 1-carbon groups
- Conversion of homocysteine to methionine in collaboration with vitamin B12
- THFA is “recycled” by vitamin B12 (see further into the lecture why this is important)
