part 5 Vitamin A-D

Fat Soluble Vitamins

Vitamin A

• Named Vitamin A, also known as retinol.
• Sources are cod liver oil, butter, cheese, and milk.
• Retinol synthesizes from carotenoids, found in carrots and tomatoes.
• Retinol is converted into retinal and retinoic acid in the body.
• Retinal is further converted to 11-cis-retinal, using NADP+ as a coenzyme, which is a photosensitive prosthetic group essential for normal function of the retina.
• The retinal molecule undergoes isomerisation upon exposure to a photon of light at the correct wavelength and is regenerated by the RPE65 enzyme.
• Retinoic acid supports embryonic development, growth, immune function, and the maintenance of epithelial tissue including skin.
• Retinoic acid is also used as a treatment for psoriasis and acne.
• Deficiency symptoms worldwide include night blindness, dry/hyperkeratotic skin, skin infection, corneal damage, and blindness.
• Supplements may be required by breast feeding women to compensate for infant's supply, or in patients unable to absorb it.
• Using retinoic acid in pregnancy is dangerous to unborn children.
• Hypervitaminosis A, or excessive intake from supplements or diet, especially liver, can lead to liver damage.

Vitamin D

• Named Vitamin D, also known as calciferol.
• Ergocalciferol is found in fungi sources such as mushrooms.
• Cholecalciferol is found in animal sources include fatty fish, cod liver oil, and egg yolk.
• The body forms vitamin D3 under UV light from provitamin precursors, 7-dehydrocholesterol, in the skin when exposed to sunlight
• Calciferol is converted into calcifediol in the liver, then altered in the kidney to produce calcitriol.
• Calcitriol stimulates synthesis of specific proteins that act as Ca2+ carriers in bone and intestine, increasing absorption of dietary Ca2+, and releasing Ca2+ from bone, with PO4 passively following the Ca2+ movements.
• Calcitriol maintains Ca2+ and PO4 at new bone formation sites for proper skeleton formation
• Deficiency can cause rickets in children, characterized by distortion of the long leg bones, distortion of the bones in the pelvis and spine, and bones of the pelvis and spine.
• Deficiency in adults leads to osteomalacia, which causes bone softening.
• Adequate synthesis of vitamin D depends on exposure to UV light.
• Night workers and miners are traditionally prone to vitamin D deficiency.
• Rate of synthesis also depends on skin pigmentation.
• Melanin protects skin cells by preventing UV penetration, thus reducing the efficiency of conversion of 7-dehydrocholesterol.
• Toxicity is caused by hypercalcemia, which can lead to calcium deposits in organs such as the kidneys, liver, and heart, as well as anorexia, insomnia, and abnormal bone formation.

Vitamin A, also known as retinol, is derived from sources like cod liver oil and carotenoids. Within the body, retinol converts into retinal and retinoic acid, crucial for vision, embryonic growth, and immune function. Deficiencies can lead to night blindness and skin issues.