Vitamins Overview Quiz

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Questions and Answers

Which of the following statements about water-soluble vitamin absorption is accurate?

Thiamine absorption can occur via both passive and active transport. (correct)

Folate absorption is independent of intrinsic factors.

Biotin absorption relies solely on passive diffusion.

Cobalamin absorption requires vitamin K supplementation.

What is the primary role of vitamin C in the body?

It is critical for the absorption of fat-soluble vitamins.

It acts primarily as a reducing agent and coenzyme in hydroxylation reactions. (correct)

It is mainly involved in the metabolism of carbohydrates.

It serves as a cofactor in the synthesis of hemoglobin.

What condition is associated with vitamin C deficiency?

Scurvy, which presents with sore gums and fragile blood vessels. (correct)

Beriberi, affecting cardiovascular health.

Rickets, characterized by bone weakness.

Pellagra, associated with niacin deficiency.

How does vitamin C affect iron absorption in the intestine?

It promotes the absorption of iron. Signup and view all the answers

Which dietary source is notably high in vitamin C?

Blackcurrants Signup and view all the answers

Which of the following are true dietary sources of Vitamin A?

Liver and dairy products Signup and view all the answers

What is the role of retinol binding protein in the body regarding Vitamin A?

It transports Vitamin A in the bloodstream Signup and view all the answers

What clinical sign is NOT associated with Vitamin A deficiency?

Alopecia Signup and view all the answers

What factor does NOT affect the absorption of fat-soluble vitamins?

Dietary fiber intake Signup and view all the answers

Which statement correctly describes the function of retinoic acid?

It acts as a gene regulator Signup and view all the answers

What would be a consequence of chronic excess intake of Vitamin A?

Damage to the liver and bones Signup and view all the answers

Which fat-soluble vitamin is primarily obtained from gut micro-flora?

Vitamin K2 Signup and view all the answers

Which of the following is NOT a function of Vitamin A in the body?

Iron absorption enhancement Signup and view all the answers

What is a primary function of Vitamin D?

Regulation of calcium absorption and homeostasis Signup and view all the answers

Which condition is NOT directly associated with Vitamin D deficiency?

Dentinogenesis imperfecta Signup and view all the answers

What is the least toxic vitamin based on the given information?

Vitamin E Signup and view all the answers

Which of the following is a source of Vitamin K?

Green leafy vegetables Signup and view all the answers

Which vitamin can be synthesized in the skin with sunlight exposure?

Vitamin D Signup and view all the answers

What condition in adults is primarily caused by Vitamin D deficiency?

Osteomalacia Signup and view all the answers

What is the primary role of Vitamin E in the body?

Antioxidant in cell membranes Signup and view all the answers

What is the possible consequence of Vitamin K deficiency?

Prolonged prothrombin time Signup and view all the answers

What is the role of intrinsic factor in the absorption of vitamin B12?

It complexes with vitamin B12 for absorption in the lower ileum. Signup and view all the answers

Which of the following is a potential consequence of vitamin B12 deficiency?

Demyelination and neurological effects. Signup and view all the answers

What are the primary dietary sources of vitamin B12?

Fish, poultry, and dairy products. Signup and view all the answers

Under what condition is a dietary deficiency of vitamin B12 most likely to occur?

In individuals with autoimmune diseases affecting their stomach. Signup and view all the answers

Which enzyme is NOT a cofactor for vitamin B12?

Acetyl-CoA carboxylase Signup and view all the answers

What is the primary clinical syndrome associated with severe niacin deficiency?

Pellagra Signup and view all the answers

Which vitamin is crucial for the function of acetyl-CoA carboxylase?

Biotin (B7) Signup and view all the answers

What is a common nutritional source of folate?

Fruits and Vegetables Signup and view all the answers

Which of the following is NOT a typical consequence of pyridoxine deficiency?

Glossitis Signup and view all the answers

Which of the following statements about Vitamin B12 is correct?

It is produced by bacteria and yeast. Signup and view all the answers

What is the consequence of excess raw egg white consumption in relation to biotin?

Reduced biotin availability due to avidin Signup and view all the answers

What is the RDA for pyridoxine (B6) per day?

1-1.7 mg Signup and view all the answers

What is the major health concern related to folate deficiency during pregnancy?

Foetal neural tube defects Signup and view all the answers

Study Notes

Classification of Vitamins

Vitamins can be categorized as fat-soluble or water-soluble.

Dietary Sources of Fat-Soluble Vitamins

Vitamin A: found in both animal and plant sources
- Animal: liver, dairy, egg yolk, fish oils
- Plant: beta-carotene (pro-vitamin A)
Vitamin D: found in limited natural sources
- Oily fish, eggs, liver
- Fortified foods
Vitamin E: found in various sources
- Nuts, soy beans, vegetable oil, spinach
Vitamin K: found in two forms with different sources
- Vitamin K1: green leafy vegetables
- Vitamin K2: synthesized by gut microflora in the large intestine

Absorption of Fat-Soluble Vitamins

Dependent on normal pancreatic function, intestinal cells and bile salts for lipid emulsification.

Vitamin A

First vitamin to be discovered, comprises a group of related compounds called retinoids.
Functions:
- Retinaldehyde functions as a light-sensitive pigment in vision, present in rhodopsin.
- Retinoic acid acts as a gene regulator.
Transported in blood by retinol binding protein (RBP) bound to transthyretin.
Deficiency:
- Night blindness, xerophthalmia, essential for reproduction (spermatogenesis, preventing fetal resorption).
- Can result from protein malnutrition due to lack of RBP.
Excess: Teratogenic in excess, chronic large ingestion can cause liver and bone damage, alopecia, headaches.
RDA: 600-900 RAE/day (RAE = retinol activity equivalent)

Vitamin D

Hormone-like functions, regulates calcium absorption and homeostasis, some immune functions.
Deficiency:
- Rickets (children): failure of bones to mineralize properly.
- Osteomalacia (adults): demineralization of bone.
Synthesized in skin under sunlight, deficiency common during winter or in northern regions.
Converted in the liver and kidney to calcitriol (active form).
Toxicity: Elevated plasma calcium, blood vessel contraction, soft tissue calcification.
RDA: Adequate intake for elderly is 5-15 µg/day.

Vitamin E

Group of eight tocopherols.
Antioxidant in cell membranes, limits radical damage from polyunsaturated fatty acid (PUFA) oxidation.
Deficiency:
- Rare, but may occur in fat malabsorption syndromes.
- Premature infants as it's not easily transported through the placenta.
- Anemia due to RBC membrane fragility.
- In experimental animals: testicular atrophy, skeletal and cardiac muscle affected, nervous system.
Least toxic vitamin - up to 300 mg/day causes no ill effects.

Vitamin K

Cofactor for enzymes involved in carboxylation of glutamate to γ-carboxyglutamate.
Essential for prothrombin formation and factors II, VII, IX, X.
γ-carboxyglutamate found in other proteins like osteocalcin in bone.
Warfarin is a vitamin K antagonist, used as an anticoagulant.
RDA: Not established, adequate intake is 60-120 μg/day.

Vitamin K Deficiency

Coagulation defects: increased prothrombin time.
Osteoporosis: Higher vitamin K correlates with greater bone density. Supplements may improve bone health, especially post-menopause.
Possible link to heart disease.
Deficiency often due to malabsorption, rather than dietary inadequacy.
Newborns receive a prophylactic injection of vitamin K due to lack of gut bacteria, poor milk content, and possible poor placental transfer.

Dietary Sources of Water-Soluble Vitamins

Vitamin B Complex
Vitamin C

Absorption of Water-Soluble Vitamins

Absorption mechanisms vary:
- Passive (down concentration gradient)
- Active transport
- Facilitated diffusion

Vitamin C (Ascorbic Acid)

Primary function as a reducing agent.
Co-enzyme in hydroxylation reactions, particularly proline and lysine in collagen synthesis.
Involved in carnitine synthesis.
Requires specific transporter in the intestine, maximum capacity of 1-2 g/day, plasma levels don’t increase significantly beyond 250 mg/day.
Enhances iron absorption in the intestine.
Sources: Blackcurrants, guava, citrus fruits.

Vitamin C Deficiency

Scurvy: Sore and spongy gums, loose teeth, fragile blood vessels, anemia, fatigue, defective connective tissue due to collagen issues.

Vitamin C and Colds

High doses (100x RDA) have been used to treat type IIb hyperlipoproteinemia.

Niacin

Sources: Grains, milk, liver.
RDA: 12-16mg/day (7mg/1000kcal).

Niacin Deficiency

Slower metabolism, decreased cold tolerance.
More severe deficiency: Pellagra, deficiency of both niacin and tryptophan.
Pellagra symptoms:
- Photosensitive dermatitis
- Diarrhea
- Dementia (may be due to reduced tryptophan, affecting serotonin synthesis)
Maize is low in niacin and tryptophan, leading to niacin deficiency.

Pantothenate (B5)

Functional moiety of Coenzyme A.
Plays a central role in energy metabolism and fatty acid synthesis.
Deficiency is rare due to wide availability in diet.
RDA: Not established, adequate intake: 4-5 mg/day.

Pyridoxine (B6)

Includes pyridoxine, pyridoxamine, and pyridoxal.
Pyridoxal phosphate acts as a coenzyme for many enzymes, especially those involved in amino acid metabolism (e.g., aminotransferases).
Clinical deficiency is rare. In experimental animals, it leads to increased steroid hormone sensitivity.
Some evidence links low B6 intake to poor breast cancer prognosis.
Sources: Especially raw food, heating can react with lysine.
RDA: 1-1.7 mg/day.

Biotin (B7)

Coenzyme in carboxylation reactions, such as:
- Acetyl CoA carboxylase
- Pyruvate carboxylase
Widely available in diet, also synthesized by gut bacteria.
Deficiency is rare, but can cause dermatitis, alopecia, glossitis, nausea, and anorexia.
Raw egg white contains avidin, which binds biotin tightly, excess consumption can lead to deficiency.
RDA: Not established, adequate intake: 20-30 µg/day.

Folic Acid (B9)

Functions as a one-carbon carrier in the synthesis of amino acids, purines, and thymine.
Sources: Fruits, vegetables, supplements.
RDA: 300-400 µg/day.
Increased intake (200-400 µg/day) recommended before and during pregnancy.

Folate Deficiency

Macrocytic (megaloblastic) anemia: Purine deficiency affects DNA synthesis, particularly in bone marrow, leading to abnormal blood cell development.
In pregnancy:
- Fetal neural tube defects, spina bifida.
- Low birth weight.

Vitamin B12 - Cobalamin

Only produced by bacteria/yeast, obtained by animals through their flora or other animals.
Sources: Liver, meat, milk, eggs.
Absorption requires “intrinsic factor”, a glycoprotein produced in the stomach: Complexes with B12 and is absorbed in the lower ileum.
Significant amounts are stored in the body (4-5 mg), enough for a few years.
Cofactor for:
- Leucine aminopeptidase
- Methylmalonyl-CoA mutase
- Methionine synthase (folate connection), involved in methyl (CH3) group transfer.

Vitamin B12 Deficiency

Megaloblastic anemia due to folate deficiency.
Neurological effects: Demyelination, nerve cell death, numbness, subacute combined degeneration of the spinal cord.
RDA: 1.4-2.4 µg/day.

Vitamin B12 Deficiency Causes

Dietary deficiency rare (except in vegans).
Intestinal disease: Lack of absorption in the lower ileum.
Bacterial overgrowth: Certain bacteria require B12, overgrowth can interfere with absorption.
Gastric malfunction: Autoimmune disease, malignancy, gastrectomy can lead to lack of intrinsic factor.

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Description

Test your knowledge on the classification, dietary sources, and absorption of fat-soluble vitamins. This quiz covers essential information about Vitamin A, D, E, and K, including their sources and functions in the body.