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This fat-soluble vitamin helps keep your eyes healthy, supports immunity, fights free radicals, and is critical for fetal development.
By: Mercura Wang
Vitamin A is a fat-soluble vitamin with multiple vital functions in the body. It supports normal cellular reproduction and is essential for optimal vision. In addition, vitamin A plays a critical role in the proper development of an embryo and fetus.
Vitamin A deficiency is prevalent in developing nations but rare in developed countries. Less than 1 percent of the American population was deficient in 2013. Some experts believe vitamin A toxicity from synthetic supplements is more common in the United States than deficiency.
What Are the Signs and Symptoms of Vitamin A Deficiency?
A prolonged vitamin deficiency within the diet causes primary vitamin A deficiency. Secondary vitamin A deficiency can result from reduced bioavailability of provitamin A carotenoids (a particular food’s normally absorbable fractions of vitamin A) or from interference with the normal absorption, storage, or transport of vitamin A. Medical conditions such as celiac disease, cystic fibrosis, pancreatic insufficiency, duodenal bypass, chronic diarrhea, bile duct obstruction, and cirrhosis may lead to interference with the absorption or storage of the vitamin. Prolonged protein-energy undernutrition can also contribute to deficiency due to both dietary insufficiency and impaired vitamin A storage and transport. Zinc deficiency in alcoholics may also result in secondary vitamin A deficiency.
Limited research indicates genetic variability in the conversion rates of beta carotene into vitamin A. Specific variations (polymorphisms) in the BCMO1 gene have been identified, which can reduce the activity of the BCMO1 enzyme in humans.
Mild deficiency symptoms include fatigue, vulnerability to infections, and reproductive challenges. More notable vitamin A deficiency signs and symptoms include:
Night blindness: Night blindness is often the initial indication of vitamin A deficiency. Since vitamin A plays a critical role in regenerating visual pigment, insufficient levels can result in night blindness due to impaired regeneration of visual pigment in retinal rods.
Conjunctival xerosis: This is the dryness of conjunctiva, the clear, thin membrane that protects our eyes.
Corneal xerosis (corneal dryness).
Bitot’s spots: Bitot’s spots are irregular and foamy patches formed by the buildup of keratin on the white of the eyes. They typically manifest in children between the ages of 3 and 6.
Keratomalacia: Keratomalacia occurs when the cornea becomes ulcerated and begins to liquefy. It is one of the most severe signs of deficiency and has the potential to penetrate and destroy the cornea within days. It also portends to the death of children in developing countries, with 50 percent dying within a year of losing their vision.
Retinopathy: Retinopathy refers to a group of disorders affecting the retina. It’s the leading cause of preventable blindness.
Dry skin or hair.
Complications
The complications of vitamin A deficiency include:
Xerophthalmia, the collection of signs and symptoms of vitamin A deficiency related to the eyes (listed above).
Poor immunity: The lack of vitamin A generally leads to impaired immunity.
Stunted growth.
Thickened organ linings: The linings of the lungs, intestines, and urinary tract become thicker and less flexible.
Anemia.
Higher risk of respiratory illness.
Permanent vision loss or blindness: Many symptoms of vitamin A deficiency can lead to blindness.
Infertility.
Death: Over 50 percent of children experiencing severe vitamin A deficiency may not survive.
What Are the Health Benefits of Vitamin A?
When we consume foods with vitamin A (in the form of retinyl esters, a combination of fatty acid and retinol), our body absorbs it mainly in the small intestine, where these retinyl esters are broken down into retinol. A small part of the vitamin A we consume is also converted into retinoic acid in the cells of the small intestine.
We also consume foods with carotenoids, such as orange and yellow vegetables and fruits. After being absorbed, some carotenoids are converted into vitamin A (retinaldehyde) in different organs and tissues.
Around 90 percent of the vitamin A we obtain from our diet is stored in the liver. When our body needs vitamin A, the vitamin is taken from this storage in the form of retinol. Once released from the liver, retinol travels in the bloodstream, and about 95 percent of it attaches to a protein called retinol-binding protein (RBP), which helps transport vitamin A to different parts of the body.
After being used by various organs and tissues, vitamin A is removed from the body through feces and urine. Retinol can be further converted into retinoic acid, which exits the body through bile and feces. The time it takes for half of the retinol (i.e., half-life) to be removed can vary, ranging from two to nine hours. However, the overall half-life of vitamin A (including all its forms) is about 12 days.
Vitamin A is essential for the following functions:
Vision health: The retina has two types of light-sensitive cells called rods and cones. When light particles enter the lens, rods and cones turn them into electric signals for the brain to understand. In low-light conditions, retinaldehyde (vitamin A compound) permeates rod cells, where it combines with a protein to make a visual pigment. Light hitting it triggers a reaction, leading to an electric signal that travels to the brain through the optic nerve, creating the sensation of sight. After doing its job, the retinaldehyde converts back into retinol to start the process again. Similar cycles occur with cone cells, which help us see different colors. Vitamin A is crucial for this entire process, as well as for eye development.
Cellular differentiation: Vitamin A is essential for normal cell differentiation—which occurs during cell renewal—especially in tissues such as the skin and mucous membranes. Vitamin A also has widespread effects on metabolism, interacting with hormones such as thyroid, insulin, and corticosteroids. This interaction is especially important for wound healing, as it boosts the growth and reproduction of skin cells, blood vessels, and collagen.
Gene regulation: In our cells, vitamin A takes different forms, such as retinoic acid. This acid acts like a hormone, affecting gene expression and various body processes. The active forms of vitamin A bind to specific proteins, which act as on-off switches for genes. These switches can pair up or mix and match, regulating gene activity. Vitamin A can also interact with other hormones, including vitamin D and steroids, thus influencing a broad range of genes. Vitamin A’s involvement in cellular processes affects over 500 genes. It’s also linked to insulin resistance and has implications for lipid metabolism and heat production in fat tissue.
Reproduction function: Retinoic acid is critical for the proper development of embryos and plays a key role in shaping their limbs, hearts, eyes, and ears. Imbalances in vitamin A levels, both excessive and deficient, are recognized for their potential to induce birth defects.
