Liposoluble vitamin found:
- in the form of retinol in foods of animal origin, in particular liver, milk and egg yolk;
- in foods of plant origin, particularly those with a yellow, orange or bright green colour (carrots, apricots, pumpkin, parsley, broccoli, etc.), in the form of carotenes, compounds converted to retinol in the liver by means of metabolic processes.
At least four different physiological functions are associated with vitamin A:
- visual – one of its derivatives (retinal) is one of the main components of the photosensitive pigments essential for vision;
- somatic - it contributes to the formation and regeneration of all covering and lining tissues (skin, epithelium, lungs, intestines, etc.) and is necessary for cell multiplication and detoxification;
- reproductive – a woman requires vitamin A for oogenesis and development of the placenta and fetus and the man to produce testosterone and sperm;
- antioxidant, principally due to the activity of the carotenes which help repair damage caused by smoking, pollution and stress and prevent tumours.
Vitamin A deficiency may cause skin and tissue alterations, poor night vision (nyctalopia), dryness of the conjunctiva and cornea (xerophthalmia) and, in severe cases, arrested growth and keratomalacia (degeneration of the cornea possibly leading to blindness).
Excessive intake of vitamin supplements and synthetic compounds may cause Vitamin A overdose (rarely caused by eating foods with a high vitamin A content) with nausea, vomiting, headache, dry and hyperpigmented skin, joint pain, enlarged liver, hair loss, anemia and neurological symptoms.
Men: 700 RE/day
Women: 600 RE/day (during pregnancy: 700 RE/day, while nursing: 950 RE/day)
(expressed in retinol equivalents (RE) according to the following formula: 1 mg retinol = 6 mg of β-carotene = 1 RE)