A group of natural and synthetic chemicals that exert a hormone like activity.
Helps regulate growth through cell proliferation and differentiation.
Mediates fetal growth, morphogenesis and maturation of multiple organs, including the respiratory system according to animal studies.
A component of visual pigment.
Maintains specialized epithelium.
Retinol is the transport form of vitamin A.
Retinol ester is the storage form of vitamin A.
Retinol is oxidized to aldehyde retinal used in retinal pigment, and to retinoic acid.
Retinol transported in chylomicrons to the liver for esterification and storage.
Vitamin A is a fat-soluble vitamin that occurs in multiple chemical forms.
It is a transcription factor ligand with roles in gene regulation for morphogenesis, differentiation, and proliferation, which collectively are responsible for the integrity of epithelial tissue. Vitamin A deficiency has been shown to induce keratinizing desquamative, squamous metaplasia in animal models.
Vitamin A deficiency causes metaplasia and keratinization of the corneal and conjunctival epithelium, leading to ulceration, scarring, and blindness.
Vitamin A is essential for the formation and maturation of keratinocytes, which are epithelial cells that produce the structural protein keratin; deficiency leads to abnormal keratin protein differentiation and skin hyperkeratosis.
Vitamin A is an integral part two phototransduction the process by which retinol rods and cone cells convert light into electrical signals.
Vitamin A deficiency commonly manifest eyedisease ranging from dryness to blindness, and dermatologic disorders of from xerosis or pruritus.
Dietary sources include liver, fish eggs, milk butter, yellow and leafy green vegetables.
Dietary sources contain carotenoids, the most important of which is beta-carotene, which have provitamins which are then metabolized to active vitamin A.
Digestion and absorption of carotenes and retinoids require bile, pancreatic enzymes and some levels of antioxidant activity in food.
More than 90% of body’s stores in the liver, and mainly in the perisinusoidal stellate cells.
Reserve is sufficient for 6 months in normal individuals with a normal diet.
Vitamin A deficiency affects 190 million preschool aged children and 19 million pregnant worldwide (WHO).
Vitamin A deficiency is the underlying cause of 650,000 early childhood deaths (Rice AL).
Chronic vitamin A deficiency may increase risks of complications and death during pregnancy and in the postpartum period.
Chronic vitamin A deficiency may adversely affect embryogenesis and postnatal development, as based on animal studies.
Retinoic acid can be absorbed unchanged and represents a small fraction of vitamin A in the blood and is active in epithelial differentiation and growth.
Retinoic acid derived from vitamin A or Beta-carotene acts on bronchial epithelium and induces mucous formation and blocks squamous differentiation.
It is suspected that perturbations in retinoid signaling may contribute to carcinogenesis in lung cancer.
In chronically undernourished population, maternal repletion with Vitamin A before, during and after pregnancy improved lung function in offspring (Checkley W).
Maternal Vitamin A deficiency is widespread in low-income countries.
WHO estimates almost 20 million pregnant women to be Vitamin A deficient, with serum retinol concentration below 0.70 micromol/L, and 9 million have gestational night blindness.
Retinoic acid does not maintain vision.
Increased intake of dietary vitamin A is associated with decreased risk of incident cutaneous squamous cell carcinoma.
Vitamin A is essential for the healthy growth and maturation of skin cells.
Eating a healthy diet rich in vitamin A may reduce risk of getting squamous cell skin cancer.
The diet and skin cancer results of participants in 2 large, long-term observational studies: the Nurses’ Health Study, which followed 121,700 women from 1984 to 2012, and the Health Professionals Follow-Up Study, which followed 51,529 men from 1986 to 2012 (Kim J).
Higher total vitamin A was associated with a reduction in squamous cell carcinoma risk.
Higher intakes of retinol and some carotenoids are associated with a reduction in squamous cell carcinoma risk.
The majority of vitamin A came from the participants’ diets, particularly from fruits and vegetables