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VITAMIN D�[CHOLECALCIFEROL]

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Dr. Ashish Agravatt,

MBBS, MD.

Sunshine vitamin

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VITAMIN D

Chemistry

Sources

RDA

Metabolism

Functions

Deficiency

Toxicity

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VITAMIN D - CHEMISTRY

PROVITAMIN

7- Dehydrocholesterol

Ergosterol

VITAMIN

Vitamin D3

[Cholecalciferol]

Vitamin D2

[Ergocalciferol]

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Vitamin D is a sterol

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VITAMIN D - SOURCES

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VITAMIN D - RDA

200 – 400 IU /day

[5 – 10µg/day]

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1microgram of vitamin D = 40 International Units

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VITAMIN D - METABOLISM

Forms

D3

D2

Site

Upper small intestine

Mechanism

Along with lipids

Requires bile salts

ABSORPTION

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VITAMIN D - METABOLISM

TRANSPORT

Binding to vitamin D

binding globulin

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VITAMIN D - METABOLISM

Synthesis of active form of vitamin D

1, 25-dihdroxy cholecalciferol or calcitriol

ACTIVE FORM

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VIT D synthesis

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1- α- hydroxylase

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VITAMIN D - FUNCTIONS

Calcitriol is the biologically active form of

vitamin D

Regulation of plasma calcium and phosphorus

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VITAMIN D - FUNCTIONS

Action of calcitriol on the intestine

Action of calcitriol on the bone

Action of calcitriol on the kidney

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VITAMIN D - FUNCTIONS

Action of calcitriol on the intestine

    • Increases the intestinal absorption of calcium and phosphate
    • By increased synthesis of calcium binding protein

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VITAMIN D - FUNCTIONS

Action of calcitriol on the bone

    • Mineralization of bone at low doses
    • Mobilization of calcium from bone at high doses

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VITAMIN D - FUNCTIONS

Action of calcitriol on the kidney

    • Increased reabsorption of calcium and phosphorus
    • Decreased excretion of calcium and phosphorus

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VITAMIN D - DEFICIENCY

Causes

Inadequate supply

Impaired absorption

Impaired production of 25hydroxy vitamin D3

Impaired production of 1, 25 dihydroxy vitamin D3

Resistant to the effects of 1, 25 dihydroxy vitamin D3

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VITAMIN D - DEFICIENCY

CLINICAL FEATURES

Children

Adults

Children

Rickets

Adults

Osteomalacia

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RICKETS

Features

Delayed milestones

Delayed closure of anterior fontanelle

Delayed dentition

Deformities of bones

Decreased serum calcium

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VITAMIN D - DEFICIENCY

Bone deformities

Craniotabes

Frontal bossing

Rachitic rosary

Pegion chest

Knocked knee

Bowed legs

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  • The classical features of rickets are bone deformities.
  • Weight bearing bones are bent Continued action of

muscles also cause bone malformations.

  • The clinical manifestations include bow legs,

knock-knee, rickety rosary, bossing of frontal bones,

and pigeon chest.

  • An enlargement of the epiphysis at the lower end

of ribs and costochondral junction leads to beading

of ribs or rickety rosary.

  • Harrison's sulcus is a transverse depression passing

outwards from the costal cartilage to axilla. This is

due to the indentation of lower ribs at the site of the

attachment of diaphragm

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Clinical Features of Osteomalacia

  • The term is derived from Greek "osteon" = bone; and "malakia" = softness.

The bones are softened due to insufficient mineralization and increased osteoporosis. Patients are more prone to get fractures.

  • The abnormalities in biochemical parameters are a

slightly lower serum calcium, and a low serum

phosphate.

  • It may be noted that vitamin D deficiency never

produces severe hypocalcemia.

  • Serum alkaline phosphatase, bone isoenzyme,

is markedly increased.

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Knock knee deformity (genu valgum)

Windswept deformity

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Bowing of long bones in legs

Bowleg deformity (genu varum)

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Frontal bossing

Tibial bowing

Wrist enlargement

Ankle enlargement

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Rib beading (rachitic rosary)

Pot belly

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Chest deformity

Scoliosis

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Family of children with rickets

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Frontal bossing

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Fig. 7-5a, p. 222

Bowed legs – Characteristic of rickets

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Fig. 7-5b, p. 222

Beaded ribs – Characteristic of rickets

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Rachitic rosary

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OSTEOMALACIA

Causes

Inadequate exposure to sunlight

Inadequate dietary intake

Features

Demineralization occurs mainly in spine, pelvis and lower extremities

Increased softness & susceptibility to fracture

Bowing of long bones

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OSTEOMALACIA

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VITAMIN D TOXICITY

    • Causes
      • Over ingestion

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    • Features
      • Hyper calcemia
      • Metastatic calcification

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Questions?

Mmm…. Vitamin D drops!