VITAMINS

​

​

​

Dr. Ashish Agravatt , MBBS, MD.

Vitamins are micronutrients

VITAMINS

VITAMINS

Vitamins are organic nutrients that are required in small quantities for a variety of biochemical functions and which generally cannot be synthesized in the body and must be supplied by the diet

Definition

VITAMINS

Classification

Vitamin B complex

• B₁ - Thiamine
• B₂ - Riboflavin
• B₃ - Niacin
• B₅ - Pantothenic acid
• B₆ - Pyridoxine
• Biotin
• Folic acid
• B₁₂- Cobalamine

Vitamine C or Ascorbic acid

Energy-releasing

Hematopoietic

Other

B₁

B₂

B₃

Biotin

Pantothenic acid

Folic acid

Vitamin B₁₂

Pyridoxine

FAT SOLUBLE VITAMINS

VITAMIN

VITAMIN A

VITAMIN A CHEMISTRY

• Vitamin A occurs in two forms in food

RETINOIDS

RETINOL

RETINAL

RETINOIC ACID

β-ionone ring

β- CAROTENE

VITAMIN A

SOURCES

• Animal :
• Fish Liver oil : cod liver & shark liver oil
• Butter & cheeze
• milk
• egg yolk
• Plant : in form of provitamin carotenes
• Tomatoes
• Carrots
• GLV
• Spinach
• Mango
• Sweet potato

​

Polar Bear

One ounce of polar bear liver contains enough vitamin A (retinol) to kill a person!

RECOMMENDED DAILY ALLOWANCE [RDA]

• The daily requirement of vitamin A is expressed as retinol equivalents [RE]

1RE = 1µg of retinol

= 3.3 IU of retinol

ABSORPTION �TRANSPORT AND�STORAGE

VITAMIN A

RETINA

TARGET TISSUES

ABSORPTION �TRANSPORT AND�STORAGE

ABSORPTION �TRANSPORT AND�STORAGE

FUNCTIONS OF VITAMIN A

• Vision : 11-cis retinal [Wald’s visual cycle]
• Reproduction: Retinol
• Growth and differentiation : Retinoic acid
• Epithelial Integrity : Retinol
• Immunity

​

VITAMIN A AND VISION

11-Cis retinal

Opsin

Photoreceptor cells in the retina

Photosensitive pigment

WALD’S VISUAL CYCLE

WALD’S VISUAL CYCLE

VITAMIN A AND COLOUR VISION

Photoreceptor cells in the retina

Required for vision in daylight and colour identification

VITAMIN A DEFICIENCY

VITAMIN A DEFICIENCY

Deficiency manifestations of Vitamin A

1. Night Blindness or Nyctalopia

• Visual acuity is diminished in dim light. The patient cannot read or drive a car in poor light. The dark adaptation time is increased.
• Deficiency of Retinal

2. Xerophthalmia (dry eye)

​

​

• The conjunctiva becomes dry, thick and wrinkled.
• The conjunctiva gets keratinized and loses its normal transparency. Dryness spreads to cornea. It becomes glazy and lusterless due to keratinization of corneal epithelium. Infections may supercede.

3. Bitot's Spots

​

• These are seen as greyish-white triangular plaques (opaque spots) firmly adherent to the conjunctiva. This is due to increased thickness of conjunctiva in certain areas.

​

• All the ocular changes mentioned so far are completely reversible when vitamin is supplemented.

4. Keratomalacia

• When the xerophthalmia persists for a long time, it progresses to keratomalacia (softening of the cornea). There is degeneration of corneal epithelium which may get vascularized. Later, corneal opacities develop Bacterial infection leads to corneal ulceration, perforation of cornea and total blindness.

• Bitot’s spot

• Keratomalacia

DIAGNOSIS OF VITAMIN DEFICIENCY

Normal plasma vitamin

20 to 80 µg/100ml

VITAMIN A TOXICITY

• Causes
• Over ingestion

CASE

​

• A 15 year old boy in hospital OPD with complain of difficulty in vision more in the night. Patient also complain of cough and cold
• He appeared malnourished and came from poor socio economic background

​

• On examination conjunctiva was thick, dry and wrinkled .Greyish white triangular plaques adherent to conjunctiva also found. There was hyperkeratinization of skin also found
• The dark adaptation time was increased
• The laboratory investigation shows decrease serum Vitamin A level ( by Carr and Price reaction )

Questions :

• What is the most probable diagnosis of this patient ?

​

• What is the major function of vitamin A

​

• Mention the active forms of vitamin A ?

​

• Mention provitamin for vitamin A ?

​

• What enzymes are required for regeneration ?

​

• What are the deficiency manifestation of vitamin A ?

​

• What are the biological role of vitamin A apart from vision ?

​

• What are the sources of vitamin A ?

​

• What is the daily requirement of vitamin A ?

​

• What are the symptoms of hypervitaminosis A ?

​

• Why hypervitamiosis is more common in fat soluble vitamines than the water soluble vitamines ?

​

• What are Bitot’s spots ?

​

• Which is the earliest manifestation of vitamin A deficiency ?

​

• What is dark adaptation time ? In which vitamin deficiency it increases ?

​

​

• Mention the pigment in retina responsible for dim light vision ?

​

• What this pigment made of it ?

​

• Which form of vitamin is responsible for antioxidant property of vitamin A ?

​

• Which form of vitamin A has role in reproduction ?

​