Vitamin A

Vitamin A can be found in two principal forms in foods:

• Retinol, the form of vitamin A absorbed when eating animal food sources, the vitamin is found in tissues in a form of retinyl ester. It is also commercially produced and administered as esters such as retinyl acetate or palmitate.
•   Provitamin A carotenoids from plant sources as yellow/orange fruits and vegetables principally carrots  

90% of retinoids can be absorbed but only 30% of carotenoids are absorbed.

Intestinal cells can convert carotenoids to retinoids

Beta carotene is safe at any dose

Sources

Vitamin A is found naturally in many foods:

• liver (beef, pork, chicken, turkey, fish) (6500 μg 722%)
• carrot (835 μg 93%)
• broccoli leaf (800 μg 89%)
• sweet potato (709 μg 79%)
• butter (684 μg 76%)                              
•                                       
• kale (681 μg 76%)
• spinach (469 μg 52%)
• pumpkin (400 μg 41%)
• collard greens (333 μg 37%)
• Cheddar cheese (265 μg 29%)                                   
• cantaloupe melon (169 μg 19%)
• egg (140 μg 16%)
• apricot (96 μg 11%)
• papaya (55 μg 6%)
• mango (38 μg 4%)
• pea (38 μg 4%)
• broccoli (31 μg 3%)
• milk (28 μg 3%)

Note: data taken from USDA database bracketed values are retinol activity equivalences (RAEs) and percentage of the adult male RDA, per 100 grams of the foodstuff (average).

Conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies.

Recommended daily intake

Vitamin A

10000IU or more during pregnancy lead to birth malformation

ADVICE to pregnant women for limit intake of liver and avoid cod-liver oil capsules

Metabolic functions

Vitamin A plays a role in a variety of functions throughout the body, such as:

• Vision
• Gene transcription
• Immune function
• Embryonic development and reproduction
• Bone metabolism
• Haematopoiesis
• Skin health
• Antioxidant activity
• Retinol participates in sperm development

Vitamin A deficiency

• Night blindness
• Blindness( xerophthalmia)
• Slow bone growth
• Impaired immune function
• Birth defects
• Keratinization( less goblet cells, some cells secrete keratin)
• Rough, scaly skin

nausea, jaundice, irritability, anorexia (not to be confused with anorexia nervosa, the eating disorder), vomiting, blurry vision, headaches, hair loss, muscle and abdominal pain and weakness, drowsiness and altered mental status