Vitamins Flashcards
What are vitamins?
Vitamins are organic compounds which are chemically unrelated .
They are required for the maintenance of normal health and metabolic integrity
They cannot be synthesised in the body but must be provided in the diet
They are found in minute quantities in food
They are required in very small amounts (µg or mg/day) and can thus be distinguished from essential macronutrients amino acids and fatty acids (g/day)
Name the vitamins that are essential for regulation of body processes and normal metabolic function
Vitamin A
B Vitamins - thiamine, riboflavin, niacin, B6, B12, biotin, pantothenic acid and folate
Vitamin C
Vitamin D
Vitamin E
Vitamin K
Name and explain the vitamins that can be synthesised by the body
Vitamin D: Synthesised in the skin upon exposure to the sun
Vitamin K and some B vitamins: synthesised by gut flora
Name and explain vitamins that occur in food in the form of precursors what are converted in the body to the active vitamin
Beta carotene converted to vitamin A
Tryptophan (converted to niacin B3)
Explain how the vitamins are named
Vitamins C, D and E follow logically
Vitamin F - found to be essential fatty acids
Vitamin G - found to be the same as B2
Vitamin H - same as Biotin
Vitamin K - discovered because of blood clotting studies in Denmark. Stands for Koagulation
What factors influence the solubility of vitamins?
Mode of action
Transport
Storage
Toxicity
Name the 2 categories that vitamins are divided into
Lipid soluble
Water soluble
Name the fat and water soluble vitamins
Fat soluble:
Vitamin A
Vitamin D
Vitamin E
Vitamin K
Water soluble vitamins:
Vitamin B’s
Vitamin C
Give some factors that influence the utilisation of vitamins
Availability
Anti-vitamins
Provitamins
Biosynthesis in the gut by bacterial flora
Intestinal disease
Interaction of other nutrients
Explain fat soluble vitamins
Found with fat in food
Specific mechanism for absorption and transport (sae as other fats/lipids)
Transported attached to protein
Often stored in the body - stored in liver or in fatty tissues, Vitamin A and D stored in the liver and may be toxic
Toxicity is more common as a result of excessive intake
Rarely act as coenzymes - except vitamin K
Explain the function and deficiency of the following vitamins and give names of each:
Vitamin A
Vitamin D
Vitamin E
Vitamin K
Vitamin A: retinol, retinal, retinoic acid
Function:
Visual pigments in the retina
Gene expression
Cell differentiation
Deficiency:
Night blindness
Keratinisation
Xerophthalmia
Vitamin D: calciferol
Function:
Maintenance of calcium balance
Intestinal absorption of calcium
Mobilisation of bone minerals
Deficiency:
Rickets (children) - poor mineralisation of bone
Osteomalacia (adults) Demineralization of bone
Vitamin E: tocopherols, tocotrienols
Function:
Antioxidants, especially in membranes
Deficiency:
Serious neurological dysfunction
(very rare)
Vitamin K: phyloquinones, menaquinones
Fucntion:
Coenzyme in formation of carboxy glutamic acid in the enzymes of the blood clotting cascade and bone matrix
Deficiency:
Impaired blood clotting Haemorrhagic disease
What are the functions of Vitamin A?
Helps our cells grow and develop
Supports vision
Supports our immune system
Supports the healthy development of the baby
Explain Vitamin A absorption and transport
Retinyl ester serves as the main storage form of retinol, acts as the primary transport form of newly arrived Vitamin A, and acts as the precursor for Vitamin A metabolites
Explain storage and excretion of vitamins
Most of the body’s vitamin A is sored in the liver in the form or retinyl esters
Retinol can be converted into retinoic acid and excreted into the bile and faeces. The elimination half-life of retinol may range from 2 to 9h; however; the half-life of Vitamin A is about 12 days
Name some foods that contain vitamin A
Vitamin A (retinol):
Dairy - milk, eggs, cheese, yoghurt
Meat - steak
Vitamin A (carotenoids):
Peppers
Melon
Spinach
Sweet potato
Carrot
Mango
Papaya
What is the DRV for Vitamin A?
Ages 1-6:
Males: 400 ug/day
Females: 400 ug/day
Ages 7-10:
Males: 500 ug/day
Females: 400 ug/day
Ages 11-14:
Males: 600 ug/day
Females: 600ug/day
Ages 15 - 18:
Males: 700 ug/day
Females: 600 ug/day
Age 19-64:
Males: 700 ug/day
Females: 600 ug/day
Ages 65 - 74:
Males: 700 ug/day
Females; 600 ug/day
Ages 75+
Males: 700 ug/day
Females: 600 ug/day
What is the RNI and SI for vitamin D
10 micrograms per day for adults (including pregnant and breastfeeding women) and children ages 4 yrs and older
Safe intake of 8.5 to 10 micrograms per day for infants up to 12 months
Explain Vitamin D
Vitamin D is a fat-soluble vitamin that is naturally present in a few foods, added to others, and available as a dietary supplement.
It is also produced endogenously when UV ryas from sunlight strike the skin and trigger Vitamin D synthesis
Vitamin D is obtained from sun exposure, foods, and supplements
Explain Vitamin D deficiencies
Without sufficient Vitamin D, bones can become thin, brittle, or misshapen
Vitamin D sufficiency prevents rickets in children and Osteomalacia in adults
Together with calcium, Vitamin D also helps protect older adults from osteoporosis
Hypocalcaemia tetany (involuntary contraction of muscles, leading to cramps and spasms)
Name food sources of Vitamin D
Eggs
Meat
Dairy
Fish
Leafy greens
Explain Vitamin E
Vitamin E is the collective name for a group of fat-soluble compounds with distinctive antioxidant activities
Vitamin E exists in eight chemical forms (alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol) that have varying levels of biological activity. Alpha- (or α-) tocopherol is the only form that is used in the human body.
Explain the function of Vitamin E in the body
Protects cells from the damaging effects of free radicals, which are molecules that contain an unshared electron. Free radicals damage cells and might contribute to the development of cardiovascular disease and cancer.
Immune function, cell signalling, regulation of gene expression, and other metabolic processes.
Inhibits the activity of protein kinase C, an enzyme involved in cell proliferation and differentiation in smooth muscle cells, platelets, and monocyte
Explain absorption and transport of Vitamin E
Vitamin E is absorbed in the small intestine in the same process as lipids and transported via the blood stream
Explain storage and excretion of Vitamin E
Vitamin E is stored in the liver and fatty tissues.
Unabsorbed vitamin E is excreted via faeces.
Additionally, vitamin E is excreted by the liver via bile into the intestinal lumen, where it will either be reabsorbed or excreted via faeces, and all the vitamin E vitamers are metabolised and then excreted via urine.
What is the DRV for Vitamin E?
4 mg a day for men
3 mg a day for women
Explain Vitamin K
Vitamin K, the generic name for a family of compounds with a common chemical structure of 2-methyl-1,4-naphthoquinone, is a fat-soluble vitamin that is naturally present in some foods and is available as a dietary supplement
Includes phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2). Menaquinones have unsaturated isoprenyl side chains and are designated as MK-4 through MK-13, based on the length of their side chain.
Almost all menaquinones, particularly the long-chain menaquinones, are also produced by bacteria in the human gut
Explain the function of Vitamin K
Vitamin K functions as a coenzyme for vitamin K-dependent carboxylase, an enzyme required for the synthesis of proteins involved in haemostasis (blood clotting) and bone metabolism and other diverse physiological functions.
Explain absorption and transport of Vitamin K
Like dietary lipids ingested vitamin K is incorporated into mixed micelles via the action of bile and pancreatic enzymes, and it is absorbed by enterocytes of the small intestine. From there, vitamin K is incorporated into chylomicrons, secreted into the lymphatic capillaries, transported to the liver, and repackaged into very low-density lipoprotein
Explain storage and excretion of Vitamin K
Compared to the other fat-soluble vitamins, very small amounts of vitamin K circulate in the blood. Vitamin K is rapidly metabolised and excreted.
The body retains about 30-40% per oral physiological dose.
About 20% is excreted in the urine and 40% to 50% in the faeces via bile.
Explain Vitamin K deficiencies
Bleeding and haemorrhage due to significant increases in prothrombin time (blood clotting).
Because vitamin K is required for the carboxylation of osteocalcin in bone, vitamin K deficiency could also reduce bone mineralisation and contribute to osteoporosis.
Vitamin K deficiency can occur during the first few weeks of infancy due to low placental transfer of phylloquinone, low clotting factor levels, and low vitamin K content of breast milk.
Name food sources that contain Vitamin K
Tomatoes
Died fruits - apricots, raisins
Nuts - chestnuts, walnuts, almonds
Broccolis
Spinach
Courgette
What is the DRV for Vitamin K
Adults needs approximately 1 microgram a day of Vitamin K for each Kg of they body weight
Explain water soluble vitamins
Not stored (apart from B12)
Enter the body freely, absorbed directly into blood stream, dissolves in intra and extra cellular fluids and is therefore transported in free form
Higher turnover in the body with little storage
Excrete it easily in urine, generally not harmful but in high doses can be
Mainly coenzymes in energy metabolism
Prone to leaching from food, more sensitive to heat
Explain the function and deficiency of the following water-soluble vitamins:
Vitamin B
Vitamin C
Vitamin B:
Function: Enzyme co-factor
Deficiency: Varies depending on the B vitamin
Vitamin C:
Function: Collagen synthesis, Enzyme co-factors, Antioxidant
Deficiency: Scurvy, Impaired wound healing, Subcutaneous haemorrhage
Explain Vitamin C
Ascorbic acid
(L-ascorbic acid is a white, odourless and stable solid, slightly soluble in ethanol, insoluble in organic solvents and soluble in water)
It can be synthesised in plants and most animal species
From D-glucose and D-galactose
But cannot be synthesised by humans
Or primates, guinea pigs, fruit eating bats, certain birds and many fish since they lack the final enzyme in the synthesis of the Vitamin C
Explain the structure of Vitamin C
Structure
Potent reducing agent
Antioxidant agent
Acidic forming
Exists in two isomers (mirror – image isomers L and D)
Explain the function of Vitamin C
Plays a role in the regeneration of vitamin E
Enhances iron absorption
Vitamin C is required for collagen synthesis
Vitamin C is a cofactor for the enzymes (coenzyme) in the hydroxylation of proline and lysine in collagen synthesis
Hydroxylated proline and lysine are essential to produce normal collagen
Hydroxyproline forms the backbone for the triple helical structure of collagen molecules (tropocollagen)
Hydroxylysine is required for the cross linking of collagen (which increases the strength and elasticity of collagen)
Explain Vitamin C absorption and transport
Readily absorbed in small intestine
Energy dependant absorption (ATP)
70 to 90% of average intake absorbed (30-200mg)
Absorption decreased to 20% with a single 5g dose and to 6% with a single 12g dose
Bioavailability from food and supplements is similar
Transported unbound in plasma
High concentrations found in intracellular fluid
Maintained by ATP driven uptake mechanism
Explain Vitamin C metabolism
Studies show that the body is saturated with vitamin C at 20mg/kg body weight on average
Normal plasma levels of vitamin range from 4 -15mg per litre
This level can be maintained with a daily intake of between 60 and 100mg vitamin C by most people
At levels greater than 200mg/day virtually all excess vitamin C is excreted in urine within 24 hours
Explain Vitamin C storage and excretion
Vitamin C is not stored in the body for long
When vitamin C free/low diet consumed there is a 3% loss per day (approximately)
On a usual intake about 50% of vitamin C is excreted in the urine as oxalic acid
Ascorbic acid, dehydroascorbic acid and other metabolites make up the remainder
When intake greatly exceeds requirement most of excess treated as unmetabolised vitamin C
Name some conditions a that are caused by Vitamin C deficiency
Scurvy
Impaired wound healing
Loss of teeth die to damaged gums (bleeding gums)
Subcutaneous haemorrhage (bleeding from capillaries)
Failure or proper cartilage and bone formation
Name some food source of vitamin C
Fruits - oranges, mango, lemon, strawberries
Vegetables - onion. spinach, coriander, tomato, parsley
Give the DRV for Vitamin C
9–13 years:
Males: 45 mg
Females:45 mg
14–18 years
Males:75 mg
Females: 65 mg
19+ years
Males: 90 mg
Females: 75 mg
