1. Preformed vitamin A or retinol: active vitamin A found in foods derived from animals.
2. Provitamin A or beta-carotene: pigment in yellow, orange, and deep green fruits and vegetables that the human body can convert to retinol.
Functions Recommended intakes (Adults) Deficiency UL and toxicity Sources Absorption issues
Vision cycle: adaptation to light and dark, tissue growth, especially skin and mucous membranes, reproduction, immune function RDA

Men: 900 mcg

Women: 700 mcg Night blindness;xerosis;xeropthalmia; susceptibility to epithelial infection; dry skin; impaired immunity, growth, and reproduction UL: 3000 mcg

Hair loss, irritated skin, bone pain, liver damage, birth defects Preformed vitamin A: liver, egg yolk, cream, butter, fortified margarine and milk

Provitamin A (carotenoids): spinach, collards, broccoli, pumpkin, carrots Absorption is most efficient when fat intake is more than 10 g/day; hindered by clinical conditions such as liver cirrhosis that affect the release of bile salts.

Vitamin D

Vitamin D functions as a hormone in the body in its active form. Vitamin D is structurally a sterol, and its precursor is found in the human skin. The two forms of vitamin D that can be used by the body are:
1. ergocalciferol (vitamin D2)
2. cholecalciferol (vitamin D3)
Functions Recommended intakes (Adults) Deficiency UL and toxicity Sources Absorption issues
Absorption of calcium and phosphorous, calcification of bones and teeth, growth AI


19-50 yrs: 5 mcg

51-70 yrs: 10 mcg

70+: 15 mcg Rickets and growth retardation in children,osteomalaciain adults UL: 50 mcg

Calcification of soft tissue, kidney damage, growth retardation Synthesized in skin with exposure to sunlight
Fortified milk, fish oils Absorbed along with fat. Hindered by malabsorption diseases such as celiac disease, cystic fibrosis, and Crohn’s disease
To better understand the synthesis and...

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