Vitamin D Overview and Dietary Sources
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Questions and Answers

What is the primary consequence of Vitamin D deficiency in children?

  • Development of osteoporosis
  • Failure of bones to grow properly (correct)
  • Increased risk of fractures
  • Delayed muscle coordination

What condition is commonly associated with the progressive loss of bone density in the elderly?

  • Rickets
  • Hypervitaminosis D
  • Osteoporosis (correct)
  • Osteomalacia

Which of the following is a symptom associated with osteomalacia?

  • Widening of growth plates
  • Bowed legs or knock-knees (correct)
  • Delayed milestones
  • Enlarged wrists

What is the upper limit of Vitamin D intake recommended to avoid toxicity?

<p>50 micrograms a day (B)</p> Signup and view all the answers

Which of the following conditions is NOT a result of Vitamin D deficiency?

<p>Hypervitaminosis D (A)</p> Signup and view all the answers

What are the two main forms of vitamin D found in dietary sources?

<p>Vitamin D2 and Vitamin D3 (C)</p> Signup and view all the answers

Which of the following countries reports a very high prevalence of vitamin D deficiency?

<p>India (A)</p> Signup and view all the answers

What is the recommended daily allowance of Vitamin D for adults?

<p>800 IU (B)</p> Signup and view all the answers

Which of the following is NOT a dietary source of Vitamin D?

<p>Chicken (A)</p> Signup and view all the answers

What role does Vitamin D play in the body?

<p>It functions similarly to a hormone. (C)</p> Signup and view all the answers

Which statement about vitamin D metabolism is correct?

<p>Vitamin D3 can be synthesized from cholesterol. (B)</p> Signup and view all the answers

What is the consequence of chronic vitamin D deficiency?

<p>Reduced bone density and rickets in children. (C)</p> Signup and view all the answers

What is the primary function of the 1-hydroxylase enzyme in vitamin D metabolism?

<p>To add a hydroxyl group to 25-hydroxy vitamin D3 (B)</p> Signup and view all the answers

Which food has the highest amount of vitamin D per 100 grams?

<p>Sea fish (A)</p> Signup and view all the answers

What is the chemical name of vitamin D2?

<p>Ergocalciferol (B)</p> Signup and view all the answers

What is the inactive form of vitamin D that is created in the kidney?

<p>24,25-dihydroxy vitamin D3 (B)</p> Signup and view all the answers

Which vitamin D form undergoes the first hydroxylation in the liver?

<p>Cholecalciferol (A)</p> Signup and view all the answers

What is the primary storage form of vitamin D in the body?

<p>25-hydroxy vitamin D3 (D)</p> Signup and view all the answers

Which of the following statements about 7-dehydro-cholesterol is true?

<p>It is necessary for the formation of vitamin D3. (D)</p> Signup and view all the answers

How long can vitamin D typically be stored in the liver?

<p>3 months (C)</p> Signup and view all the answers

What is the active form of vitamin D called?

<p>Calcitriol (C)</p> Signup and view all the answers

Which function is NOT directly associated with vitamin D?

<p>Promotion of muscle hypertrophy (A)</p> Signup and view all the answers

Which vitamin D status is classified as 'insufficiency' according to the US Endocrine Society classifications?

<p>21-29 ng/mL (A)</p> Signup and view all the answers

What is the result of calcitriol entering intestinal cells?

<p>Release of calbindin (C)</p> Signup and view all the answers

Which of the following effects of vitamin D is associated with its action on bones?

<p>Mineralization at low doses (B)</p> Signup and view all the answers

What is a potential result of calcium homeostasis regulated by vitamin D?

<p>Stimulation of cell proliferation (B)</p> Signup and view all the answers

In the context of vitamin D metabolism, what does the term 'calcitriol' refer to?

<p>Hormonal form of vitamin D (C)</p> Signup and view all the answers

Which effect on the cardiovascular system is attributed to vitamin D?

<p>Regulating blood pressure (C)</p> Signup and view all the answers

What is the effect of high doses of vitamin D on bone health?

<p>Mobilization of calcium from bone (C)</p> Signup and view all the answers

Which of the following statements about Vitamin D and immune function is true?

<p>Vitamin D helps control invading pathogens (C)</p> Signup and view all the answers

Which of the following substances is primarily released due to the action of calcitriol in the intestines?

<p>Calbindin (C)</p> Signup and view all the answers

What is the primary effect of calcitriol on the kidney regarding calcium levels?

<p>Increased calcium reabsorption (C)</p> Signup and view all the answers

What serum calcium level indicates hypocalcemia?

<p>Below 8.5 mg/dl (A)</p> Signup and view all the answers

Which hormone acts as the principal acute regulator of blood calcium levels?

<p>Parathyroid Hormone (PTH) (B)</p> Signup and view all the answers

Which of the following is NOT a cause of vitamin D deficiency?

<p>Excessive calcium intake (B)</p> Signup and view all the answers

What effect does 1,25-(OH)₂D₃ have on the gastrointestinal tract?

<p>Increases calcium absorption (A)</p> Signup and view all the answers

Which of the following is a feature of rickets?

<p>Knocked knee (A)</p> Signup and view all the answers

What happens to PTH levels when serum calcium decreases?

<p>PTH levels increase (D)</p> Signup and view all the answers

What is craniotabes?

<p>Softening of the skull bones (C)</p> Signup and view all the answers

What is the role of 1,25-(OH)₂D₃ in relation to PTH synthesis?

<p>It increases PTH synthesis (C)</p> Signup and view all the answers

Which condition is characterized by beaded ribs?

<p>Rickets (B)</p> Signup and view all the answers

Flashcards

Vitamin D forms

Vitamin D exists in two forms: D2 (Ergocalciferol) and D3 (Cholecalciferol). D3 is the natural form for animals and humans.

Vitamin D source (diet)

Dietary sources include sunlight, fatty fish (salmon, tuna), egg yolks, and fortified foods. Mushrooms also contain Vitamin D2.

Vitamin D function

Vitamin D acts like a hormone, regulating calcium levels and bone health.

Vitamin D - Cholesterol relation

Vitamin D3 is produced in the body from cholesterol, using UV-B radiation.

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Vitamin D in humans

Humans can obtain Vitamin D from food, and synthesize it from skin exposed to sunlight.

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Vitamin D deficiency prevalence

Low Vitamin D status (25(OH)D levels below 30 nmol/L) is very common globally, especially in certain regions like India and Tunisia.

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Vitamin D's chemical form

Vitamin D is a sterol with a cyclopentanoperhydrophenanthrene ring structure, similar in molecular structure to steroid hormones.

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Vitamin D3 Source

Vitamin D3 is produced in the skin when exposed to UV light from the sun. It's also obtained from foods.

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Vitamin D2 Source

Vitamin D2 comes from plants (e.g., mushrooms).

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Active Vitamin D

1,25-dihydroxy vitamin D3 (Calcitriol) regulates calcium and phosphorus absorption.

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Vitamin D Storage

The liver stores 25-hydroxy vitamin D3 for later use.

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Vitamin D activation site

The kidneys convert 25-hydroxy vitamin D3 into the active form, 1,25-dihydroxy vitamin D3.

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7-dehydrocholesterol

A precursor molecule that converts to vitamin D3 upon UV exposure.

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25-hydroxy vitamin D3

A storage form of vitamin D, produced in the liver.

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Calcitriol

Active form of Vitamin D3, crucial for bone health and calcium absorption

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Food Vitamin D sources

Food like egg, sea fish, mushrooms, fortified cereals, and milk offer various amounts of vitamins D2 & D3.

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Harrison Groove

A groove formed on the ribs due to the pulling action of the diaphragm during inspiration, making the ribs more flexible.

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Rickets

A disease in children caused by Vitamin D deficiency, leading to weak bones and deformities like bowed legs and knock-knees.

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Osteomalacia

The adult form of rickets, caused by Vitamin D deficiency, leading to soft and brittle bones.

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Osteoporosis

A condition characterized by thinning of bones and reduced density, making them more prone to fractures, especially common in older adults.

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Vitamin D Toxicity

Excess Vitamin D can cause hypervitaminosis D, leading to calcification of soft tissues like lungs and blood vessels, posing health risks.

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What does Vitamin D do for calcium?

Vitamin D (calcitriol) increases intestinal calcium absorption by binding to the vitamin D receptor in intestinal cells, leading to the release of Calbindin, a calcium binding protein.

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Calcitriol's role in bone health

Calcitriol, at moderate doses, promotes bone mineralization. At higher doses, it can mobilize calcium from bone.

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Vitamin D deficiency

Vitamin D deficiency occurs when blood levels of 25(OH)D are below 20 ng/mL (US Endocrine Society) or 15 ng/mL (US IOM).

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Vitamin D sufficiency

Vitamin D sufficiency is achieved when blood levels of 25(OH)D are above 30 ng/mL or 20 ng/mL, depending on the classification system.

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Vitamin D - Liver

The liver converts vitamin D into 25(OH)D, a storage form of Vitamin D.

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Vitamin D - Kidney

The kidneys convert 25(OH)D into its active form, 1,25(OH)₂D₃ (calcitriol).

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Calcitriol's many roles

Calcitriol, the active form of Vitamin D, plays a crucial role in calcium homeostasis, bone health, muscle function, and immune modulation.

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Vitamin D and immune system

Vitamin D helps regulate immune function by influencing the development and activity of immune cells.

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Vitamin D and cellular processes

Vitamin D plays a role in cell growth, differentiation, and even apoptosis, the programmed death of cells.

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Vitamin D and other organs

Calcitriol acts on various organs, including the prostate, breast, colon, lung, and keratinocytes, influencing cellular function.

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Calcitriol's Action on Kidneys

Calcitriol increases calcium and phosphorus reabsorption in the kidneys, while decreasing their excretion.

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Hypocalcemia

Hypocalcemia occurs when blood calcium levels fall below 8.5 mg/dl, the lower limit of the normal range.

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Parathyroid Hormone (PTH) - Role

PTH is the primary regulator of blood calcium levels. It acts as a hypercalcemic hormone, increasing calcium levels in hypocalcemia.

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Calcitriol's Actions

Calcitriol increases calcium absorption in the gut, bone resorption, and calcium reabsorption in the kidneys. It also stimulates PTH synthesis.

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Maintaining Blood Calcium Levels

Low serum calcium triggers the release of PTH, which then increases calcitriol levels. This leads to more calcium mobilization from bones, reabsorption in the kidneys, and absorption from the gut.

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Vitamin D Deficiency: Causes

Vitamin D deficiency can occur due to insufficient intake, impaired absorption, inadequate production of 25-hydroxyvitamin D3, impaired production of 1,25-dihydroxyvitamin D3, or resistance to the effects of 1,25-dihydroxyvitamin D3.

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Rickets: Features

Rickets is characterized by delayed developmental milestones, delayed fontanelle closure, delayed dentition, bone deformities, and low serum calcium levels.

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Craniotabes

Craniotabes is a softening of the skull bones, leading to a 'ping-pong ball' feel, a feature of rickets.

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Frontal Bossing

Frontal bossing is a prominent forehead bulge, a characteristic feature of rickets.

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Beaded Ribs

Beaded ribs, also known as 'Rachitic Rosary', are a characteristic feature of rickets, where the rib joints become enlarged and palpable.

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Study Notes

Vitamin D Overview

  • Vitamin D is a fat-soluble vitamin; a sterol containing a cyclopentanoperhydrophenanthrene ring
  • Vitamin D functions like a hormone
  • Two forms: Vitamin D2 (Ergocalciferol) and Vitamin D3 (Cholecalciferol) which is the natural form in animals/man, created in bodies from cholesterol and 7-dehydrocholesterol
  • An alternative form of Vitamin D2 is commercially prepared from ergosterol found in yeast
  • Vitamin D's molecular structure closely resembles that of classic steroid hormones

Vitamin D Dietary Sources

  • Sunlight
  • Cod liver oil
  • Caviar
  • Mackeral
  • Salmon
  • Sardines
  • Cheese (in some)
  • Raw milk
  • Mushrooms
  • Tuna
  • Eggs
  • Oysters
  • Cerals (fortified)
  • Butter (in some)
  • Processed cheese (fortified)
  • Almond milk
  • Soy milk

Vitamin D- RDA

  • 200-400 IU/day [5-10µg/day]
  • 1 microgram of vitamin D = 40 International Units

Vitamin D Deficiency Most Common

  • Worldwide, many countries report a high prevalence of low vitamin D status (25(OH)D levels < 30 nmol/L or 1 ng/ml) in >20% of the population.
  • Common in India, Tunisia, Pakistan, and Afghanistan

Formation of Vitamin D

  • Skin (UV light): 7-dehydrocholesterol → vitamin D3
  • Liver: OH-group added (first hydroxylation). Storage form of vitamin D (3 months storage in liver)
  • Kidney: OH-group added by 1-hydroxylase (second hydroxylation). 1,25-dihydroxyvitamin D3 (or 1,25-dihydroxy cholecalciferol, 1,25-DHCC) - active form of vitamin D, a steroid hormone; 24,25-dihydroxy -vitamin D - an inactive form, ready for excretion

Calcitriol Synthesis

  • UV light → 7-dehydrocholesterol → Previtamin D → Cholecalciferol (calciol)
  • Liver → 25-OH-cholecalciferol (calcidiol)
  • 24,25-(OH)2-cholecalciferol (inactive form)
  • Kidney → Calcitriol (1,25-(OH)2-cholecalciferol - active form)

Vitamin D Transport

  • Vitamin D is transported from the intestine to the liver by binding to vitamin D-binding globulin.
  • 25-hydroxy D3 and 1,25-dihydroxy D3 are also transported in the blood by binding to vitamin D-binding globulin
  • 25-hydroxycholecalciferol is the major storage and circulatory form of vitamin D.

Vitamin D Functions

  • Calcium and Phosphorus Homeostasis: Absorption in small intestine, resorption (bone and kidney), maintains blood calcium levels
  • Bone formation: Stimulates Calcium uptake for deposition.
  • Regulation of gene expression; Cell growth
  • Regulation of immune function; Growth and bone mineralization; Control of cell proliferation, etc

Vitamin D Promotes Intestinal Calcium Absorption

  • Calcitriol enters the intestinal cell and binds to vitamin D receptor
  • The hormone-receptor complex causes the release of Calbindin
  • Increased availability of calcium-binding protein, increasing calcium absorption

Vitamin D Status in Relation to 25(OH)D Levels

  • A range of serum calcium levels (8.5-10.5 mg/dl) classified as Normal.
  • Deficiency below 20 ng/mL (50 nmol/L)
  • Insufficiency (21–29 ng/mL (52.5–72.5) nmol/liter)
  • Sufficient (>30 ng/mL)
  • Risk of toxicity (>50 ng/mL or >150 ng/mL)

Vitamin D Deficiency: Causes

  • Inadequate supply; Impaired absorption; Impaired production of 25-hydroxyvitamin D3; Impaired production of 1,25-dihydroxyvitamin D3; Resistant to the effects of 1,25-dihydroxyvitamin D3

Rickets

  • Delayed milestones; Delayed closure of anterior fontanelle; Delayed dentition; Deformities of bones; Decreased serum calcium; Enlarged wrists and ankles; Growth plate widening

Osteomalacia

  • Adult form of rickets.
  • Adult form showing porous bones

Vitamin D Toxicity

  • Hypervitaminosis D—Among the vitamins, vitamin D is the most toxic in overdoses
  • Calcification of soft tissue
  • hardening of arteries/stone formation in kidney
  • Does not occur from sunlight or dietary sources, only from supplementations

Parathyroid Hormone (PTH)

  • Principal acute regulator of blood [Ca2+]; hypercalcemic hormone in hypocalcemia.

Actions of Calcitriol on Intestine, Bone, and Kidney

  • Increased Intestinal Absorption of Calcium/Phosphate
  • Bone Mineralization at Low Doses, Calcium Mobilization From Bones at High Doses
  • Increased Reabsorption of Calcium/Phosphorous in Kidneys, Decreasing Excretion

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Vitamin D - Lecture Notes PDF

Description

This quiz covers essential information about Vitamin D, including its functions, dietary sources, and recommended daily allowances. Test your knowledge on the types of Vitamin D and how dietary habits can affect vitamin levels in the body.

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