Vitamin C: Functions and Deficiency

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Questions and Answers

What is the primary function of vitamin C in collagen formation?

Hydroxylation of proline and lysine (correct)

Maintenance of the Fe(II) necessary for proline and lysine hydroxylase activity

Reduction of dietary Fe in the stomach for absorption

Antioxidant protection of vitamins A, E, and K

What is the recommended daily intake of vitamin C for smokers?

60 mg/day

80 mg/day (correct)

100 mg/day

40 mg/day

What is the recommended daily intake of vitamin E in pregnancy?

0.6 mg/day

1 g/day

3.3 mg/day (correct)

0.7 mg/day

What is the major metabolite of vitamin C that can cause kidney stones in susceptible individuals?

Oxalate Signup and view all the answers

What is the primary function of vitamin E in the body?

To prevent oxidation of unsaturated fatty acids Signup and view all the answers

What is the typical duration of vitamin C storage in the human body?

6 months Signup and view all the answers

Which of the following foods is a rich source of vitamin E?

Wheat germ oil Signup and view all the answers

What happens when vitamin E becomes a radical?

It can be reduced to its original form Signup and view all the answers

What is the primary cause of vitamin A deficiency?

All of the above Signup and view all the answers

What is a characteristic of vitamin E deficiency in premature infants?

Haemolytic anaemia Signup and view all the answers

What is the main source of vitamin A in plant-based foods?

Green/yellow/orange vegetables and fruit Signup and view all the answers

Why is human milk not a good source of vitamin E?

Vitamin E does not cross the placenta easily Signup and view all the answers

What is the potential risk of taking high doses of vitamin C during pregnancy?

Infants with unusually high requirements Signup and view all the answers

What is the potential protective effect of vitamin E?

Against cardiovascular disease and cancer Signup and view all the answers

What is the benefit of taking megadoses of vitamin C, according to some research?

No clear benefits have been established Signup and view all the answers

What is α-tocopherol?

The most potent form of vitamin E Signup and view all the answers

What is the outcome of carotenoid cleavage?

2 retinol molecules Signup and view all the answers

What is the unit of measurement for potency of retinol?

Retinol equivalents Signup and view all the answers

Which of the following is NOT an active form of retinol?

Carotenoids Signup and view all the answers

What is the primary mechanism of action of retinoic acid in controlling protein synthesis?

Binding to specific receptor proteins in the cytosol Signup and view all the answers

What is the primary role of retinol in vision?

Converting light energy to impulses in the optic nerve Signup and view all the answers

What is the primary transport vehicle for retinol in the bloodstream?

Retinol-binding protein and pre-albumin Signup and view all the answers

What is the typical consequence of retinol deficiency in developing countries?

Night blindness followed by xerophthalmia Signup and view all the answers

What is the potential consequence of excessive retinol intake?

Dermatitis, hair loss, and mucous membrane defects Signup and view all the answers

What is the role of vitamin D in maintaining bone health?

It helps to maintain correct levels of calcium and phosphate in the blood Signup and view all the answers

What is the source of vitamin D2 (ergocalciferol)?

Plants, fungi, and moulds Signup and view all the answers

What is the clinical presentation of rickets in children?

Delayed tooth eruption, bending of long bones, and kyphosis Signup and view all the answers

What is the recommended daily intake of vitamin D by the NHS?

10 microg per day between October and March Signup and view all the answers

What is the consequence of excessive vitamin D consumption?

Hypercalcaemia, GI tract disturbances, and calcification of soft tissues Signup and view all the answers

What is the primary source of vitamin K in human milk?

Bacterial flora of the jejunum and ileum Signup and view all the answers

Why do infants have a higher risk of vitamin K deficiency?

Because the neonatal gut is sterile and unable to produce vitamin K Signup and view all the answers

What is the function of vitamin D in the body?

It maintains correct levels of calcium and phosphate in the blood Signup and view all the answers

What is the consequence of vitamin D deficiency in adults?

Osteomalacia and muscle weakness Signup and view all the answers

What is the consequence of a vitamin K deficiency?

Increased blood clotting time Signup and view all the answers

When should one limit the intake of vitamin K?

During anticoagulation therapy Signup and view all the answers

How is vitamin D3 (cholecalciferol) formed?

Through the action of UV light on 7-dehydrocholesterol Signup and view all the answers

What is the primary cause of haemorrhagic disease of the new-born?

Poor placental transfer and lack of gut flora Signup and view all the answers

What is the consequence of haemorrhagic disease of the new-born?

50% of affected babies die, and the other 50% have neurological malfunction Signup and view all the answers

Study Notes

Vitamin C (Ascorbic Acid)

Sources: citrus fruits, tomatoes, berries
Function: anti-oxidant nutrient, necessary for hydroxylation of proline and lysine in collagen formation, and reduction of dietary Fe in the stomach for absorption
Possibly protects vitamins A, E, and K from oxidation
Deficiency: Scurvy, characterized by impaired wound healing, hemorrhages, and anemia
Low vitamin C status in the elderly, alcoholics, and adolescents, especially those on 'junk' food
Smokers need twice the normal intake (80 mg/day) due to increased turnover of ascorbic acid
Megadoses: uncertain benefits, but may ease symptoms of cold, and risks of kidney stones, diarrhea, and systemic conditioning

Fat-Soluble Vitamins

Causes of deficiency: primary dietary deficiency, low fat diet, and fat malabsorption

Vitamin A

Sources: retinol from animal liver and fish liver oils, whole milk, and egg yolk; plant carotenoids (mainly β-carotene) from green/yellow/orange vegetables and fruit
Absorption: carotenoids are cleaved to 2 retinol molecules, with inefficient conversion
Active forms: retinoic acid, retinal, and β-carotene
Functions: control of protein synthesis, vision, and maintenance of epithelial cells and mucopolysaccharide synthesis
Deficiency: rare in developed countries, but common in developing countries, especially with inadequate protein diets
Deficiency symptoms: night blindness, progressive keratinization of the cornea, and finally keratomalacia and irreversible blindness
Toxicity/Teratogenicity: dermatitis, hair loss, mucous membrane defects, hepatic dysfunction, and thinning and fracture of long bones

Vitamin E

Source: vegetable oils, especially wheat germ oil, nuts, and green vegetables
Function: prevents oxidation of unsaturated/poly-unsaturated fatty acids in cell membranes and circulating lipoproteins, and acts as a free radical scavenger
Deficiency: virtually unknown, except in premature, low birth weight infants, and characterized by haemolytic anaemia
Requirements: difficult to establish, likely to be higher with high PUFA intake
Possible protective effect against cardiovascular disease and cancer

Vitamin D

A group of similar compounds, with cholecalciferol (vitamin D3) occurring naturally in animals and ergocalciferol (vitamin D2) derived from ergosterol in plants
Sources: milk and dairy products, fortified margarine, eggs, and skin formation through UV light
Function: maintains correct levels of calcium and phosphate in the blood for proper bone mineralization
Deficiency: rickets in children and osteomalacia in adults, characterized by mineral:matrix ratio decrease in bone, bending of long bones, and delayed tooth eruption
Recommendations: consider taking 10 microg between October and March for adults and children over 4 years
Toxicity: excessive consumption is toxic, causing hypercalcaemia, GI tract disturbances, and calcification of soft tissues

Vitamin K

Sources: green leafy vegetables, milk, meat, eggs, and cereals, as well as the bacterial flora of the jejunum and ileum
Function: essential for blood clotting, which depends on a cascade system of interacting proteins
Deficiency: rare, except in long-term antibiotic therapy, and characterized by defective blood clotting
Limiting intake: necessary for anticoagulation therapy, such as warfarin, and in haemorrhagic disease of the new-born

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Description

Learn about the sources and functions of Vitamin C, also known as ascorbic acid, including its role in collagen formation and as an antioxidant. Discover the effects of Vitamin C deficiency, including scurvy.