38 Questions
What is the ratio of carotene to retinol in terms of potency?
6:1
What is the primary function of retinoic acid in the body?
Hormone-like activity
During which type of vision is 11-cis retinal most important?
Scotopic vision
How is retinol transported from the liver to the tissues?
Bound to a specific retinol binding protein
What is a common association with vitamin A deficiency?
Inadequate protein diets
What is a late-stage complication of vitamin A deficiency?
Keratomalacia
What is a potential side effect of excessive vitamin A supplementation?
All of the above
What is the unit of measurement for retinol potency?
Retinol equivalents (RE)
What is the primary function of vitamin C in collagen formation?
Hydroxylation of proline and lysine
What is the recommended daily intake of vitamin C for smokers?
80 mg/day
What is a potential risk of taking megadoses of vitamin C?
Kidney stones in susceptible individuals
What is the primary cause of vitamin deficiency?
Dietary deficiency
What is the primary source of vitamin A?
Animal liver and fish liver oils
What is the effect of vitamin C deficiency on the body?
Impaired wound healing and haemorrhages
Who is at risk of vitamin C deficiency?
All of the above
What is the effect of megadoses of vitamin C on the body?
Uncertain benefits and potential risks
What is the recommended daily intake of vitamin E in pregnancy?
3.3 mg/day
What is the primary function of vitamin E in the body?
To prevent oxidation of unsaturated fatty acids
What is the outcome of a fatty acid radical reacting with oxygen?
A peroxyl radical is formed
What is the characteristic effect of vitamin E deficiency in premature infants?
Haemolytic anaemia
What is the role of vitamin E in protecting against cardiovascular disease?
It protects fatty acids and apoprotein B in LDL from oxidative damage
What is the primary source of vitamin E in the diet?
Vegetable oils, especially wheat germ oil
What is the effect of vitamin E deficiency on human milk?
It is not a significant source of vitamin E
What is the relationship between vitamin E intake and polyunsaturated fatty acid intake?
Vitamin E intake is likely to be higher with high PUFA intake
What is the primary source of vitamin K in infants?
Bacterial flora of the gut
Why do infants have a marginal insufficiency of vitamin K?
All of the above
What is the consequence of vitamin K deficiency in terms of blood clotting?
Increased blood clotting time
When should vitamin K rich foods be avoided?
During anticoagulation therapy
What is the consequence of vitamin K deficiency in newborns?
Increased risk of haemorrhagic disease
What is the outcome of haemorrhagic disease in 50% of affected babies?
Death
What is the primary mechanism by which vitamin D functions in the body?
By binding to intra-cellular receptors that eventually interact with DNA
Which of the following is a characteristic of rickets in children?
Bending of long bones and kyphosis
What is the primary source of ergocalciferol (vitamin D2)?
Plants, fungi, and moulds
What is the recommended daily intake of vitamin D by the NHS for adults and children over 4 years between October and March?
10 microg
What is the primary consequence of a vitamin D deficiency in adults?
Osteomalacia
How is cholecalciferol (vitamin D3) formed in the skin?
Through the action of UV light on 7-dehydrocholesterol
What is the primary effect of excessive vitamin D consumption?
Hypercalcaemia
What is the approximate intake of vitamin D that produces toxicity?
10 x RNI (100 microg)
Study Notes
Vitamin C (Ascorbic Acid)
- Sources: Citrus fruits, tomatoes, berries
- Functions:
- Anti-oxidant nutrient
- Hydroxylation of proline and lysine in collagen formation
- Reduction of dietary Fe in the stomach for absorption
- Possibly protects vitamins A, E, K from oxidation
- Deficiency:
- Scurvy
- Impaired wound healing, hemorrhages, and anemia
- Low vitamin C status in the elderly, alcoholics, and adolescents
- Smokers need twice the normal intake (80 mg/day) due to increased turnover of ascorbic acid
Fat-Soluble Vitamins
Vitamin A
- Sources:
- Animal liver and fish liver oils
- Whole milk and egg yolk
- Plant carotenoids (mainly β-carotene) in green/yellow/orange vegetables and fruits
- Absorption:
- Carotenoids are cleaved to 2 retinol molecules (inefficient conversion)
- Potency expressed as retinol equivalents (1 RE = 1 μg retinol)
- Active forms:
- Retinoic acid (acts as a hormone)
- Retinal (in vision)
- β-carotene (antioxidant)
- Functions:
- Controls protein synthesis
- Acts in vision (best understood function)
- Transport and storage:
- From gut to liver in chylomicrons
- From liver to tissues bound to specific retinol binding protein and pre-albumin
- Deficiency:
- Rarely seen in developed countries, but common in developing countries
- Associated with inadequate protein diets
- Affects synthesis of retinol binding protein and transport to tissues
- Night blindness, xerophthalmia, and keratomalacia
- Toxicity/Teratogenicity:
- Dermatitis, hair loss, mucous membrane defects, hepatic dysfunction, thinning and fracture of long bones
Vitamin E
- Source:
- Vegetable oils (especially wheat germ oil)
- Nuts
- Green vegetables
- Function:
- Prevents oxidation of unsaturated/polyunsaturated fatty acids in cell membranes and circulating lipoproteins
- Free radical scavenging
- Deficiency:
- Known in animals as a cause of sterility and muscular dystrophy
- Human deficiency: virtually unknown, except in premature, low-birth-weight infants
- Haemolytic anemia due to fragility of red cell membranes
Vitamin D
- A group of similar compounds
- Cholecalciferol (Vitamin D3) occurs naturally in animals
- Vitamin D2 (ergocalciferol) derived from ergosterol
- Sources:
- Milk and dairy products
- Fortified margarine
- Eggs
- Function:
- Acts to maintain correct levels of calcium and phosphate in the blood for proper bone mineralization
- Deficiency:
- Rickets in children
- Osteomalacia in adults
- Muscle weakness, bone pain, and decalcification of long bones
- Recommendations (NHS):
- Consider taking 10 μg between October and March for adults and children over 4 years
Vitamin K
- Sources:
- Green leafy vegetables
- Milk, meat, eggs, and cereals
- Bacterial flora of the jejunum and ileum
- Deficiency:
- Blood clotting is defective
- Increased blood clotting time is rare, except in:
- Long-term antibiotic therapy
- Anticoagulation therapy (Warfarin)
- Haemorrhagic disease of the newborn
Learn about vitamin C, its sources, functions, and deficiency symptoms, including scurvy.
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