Food Additives Vitamin A is a fat-soluble nutrient, also known as retinol, which exhibits higher absorption rates when consumed with fats and oils. It can be found in animal liver, cod liver oil, dairy products, and certain plants. Typically available in the form of yellow crystals or powder, it remains stable at room temperature but undergoes degradation in the presence of heat, light, and oxygen. Vitamin A plays a crucial role in visual production within the body and was initially employed for treating dry eye disease; hence its designation as an "anti-dry eye factor." Recognized by the World Health Organization as one of the four major nutritional deficiencies, severe deficiency can result in night blindness.
Vitamin A can be found in milk and dairy products: many milk and dairy products, including butter, cheese, and yogurt, have been fortified with vitamin A to enhance their nutritional content. Additionally, cod liver oil is a natural source of vitamin A and is commonly used as a supplement to meet daily vitamin A requirements.
What are the roles of vitamin A?
1) Eyes and Vitamin A
When entering a dimly lit environment like a movie theater, some individuals may experience photophobia due to a deficiency in vitamin A. Vitamin A plays a crucial role in the synthesis of retinal pigment, which is an essential component of optic pigments responsible for perceiving low light conditions. Insufficient levels of vitamin A result in reduced production of retinal pigment, leading to decreased adaptability when transitioning from bright to dark environments and prolonged time required for visual acclimation. If the deficiency persists, symptoms can progressively worsen and eventually lead to night blindness, causing difficulties in seeing objects during evening or nighttime. Additionally, vitamin A also helps prevent dryness of the conjunctiva and cornea while safeguarding overall eye health.
2）Skin and Vitamin A
Vitamin A plays a crucial role in maintaining the health of skin and mucous membranes. Beautiful, smooth skin, moisturized and lustrous hair, as well as strong and radiant nails all rely on an adequate supply of vitamin A. This essential nutrient promotes epithelial cell differentiation and proliferation, preventing keratinization disorders in the epidermis when its levels are sufficient. Insufficient intake of vitamin A can lead to damage in the skin and mucous membranes, resulting in thickened skin (dryness, flaking) with follicular keratinization such as pimples. These effects are particularly noticeable on the outer side of the upper arm and lower limb where perifollicular keratosis may cause unsightly bumps.
3) Vitamin A enhances immunity
The air or food that enters our mouth, nose, lungs, and gastrointestinal tract comes into contact with the epithelial cells on the mucous membrane (air pollution). What is the function of these epithelial cells? They serve as a protective barrier against pathogenic bacteria. Vitamin A plays a crucial role in inducing differentiation and proliferation of epithelial cells. In other words, vitamin A promotes the normal growth of this barrier to enhance immunity against colds and other illnesses. Deficiency of respiratory epithelium in vitamin A can lead to keratinization, loss of cilia, decreased resistance, increased susceptibility to infection in trachea and bronchial tubes, weakened ability to defend against germs, frequent occurrence of colds in young children, and even severe cases like bronchopneumonia.
(4) Strong bones also need vitamin A
Bone growth necessitates a delicate equilibrium between osteoblasts and osteoclasts, and an insufficiency of vitamin A will lead to a reduction in osteoclasts, excessive periosteal growth, and diminished bone cavities. Adequate levels of vitamin A are essential for promoting bone growth. Insufficient vitamin A intake results in decreased osteoclast activity, uncontrolled proliferation of osteoblasts, abnormal periosteal expansion, reduced bone cavity size, and outward extension of bone tissue such as the elongation of long bone ends observed in bovine tests.
