Vitamin A is a group of chemical compounds with a similar structure. These compounds can be divided into the following:
- Preformed vitamin A, or fat-soluble retinoids: retinol, retinaldehyde, retinoic acid;
- Provitamin A carotenoids: beta-carotene, alpha-carotene, gamma-carotene, and cryptoxanthin
Retinol and beta-carotene are the most common forms of vitamin A found in food and supplements.
Preformed vitamin A (retinol) is known as the active form of the vitamin, which our bodies can use just as it is.
Beta-carotene (provitamin A), on the other hand, needs to be converted to vitamin A in our bodies, and this process depends on many factors such as food preparation, individual differences in digestion and absorption, and genetics. Typically, a very low amount of ingested beta-carotene is actually absorbed. People with diabetes, low thyroid activity, and those who use a lot of polyunsaturated fatty acids (PUFAs), for example, have a lower ability to convert beta-carotene to A.
For the absorption of both pre- and provitamin A forms, we need dietary fat and bile salts in the intestine.
Absorption of vitamin A is reduced with alcohol use, with vitamin E deficiency, with cortisone medication, and with excessive iron intake or the use of mineral oil, as well as with exercise.
About 90% of the storable vitamin is in the liver. In addition to reducing absorption, alcohol use also depletes liver stores. The storage of vitamin A is also decreased during times of stress or illness. Also, the body needs zinc to help release stores of vitamin A for use.
How do we get vitamin A from foods?
Preformed vitamin A is found in animal-based foods. Some of the best sources are:
- Beef liver
- Chicken liver
- Cod liver oil
- Fish such as salmon, king mackerel
- Whole milk
Provitamin A comes from plant foods. Think green and orange-yellowish veggies and fruits, such as:
- Red peppers
Why is vitamin A so crucial for our health?
Here are some of its well-known roles:
Vitamin A is essential for the proper functioning of certain parts of the eye. It is needed for the formation of the so-called visual purple, which allows us to see at night. Vitamin A also helps maintain the health of the cornea (the eye covering). Vitamin A deficiency may allow irritation or inflammation of the eye tissue to occur more easily.
Growth and tissue healing.
Vitamin A is involved in the growth and division of new cells, including bone cells. Vitamin A helps our bones develop and our teeth remineralize. Without vitamin A, we can’t build bones and/or use the calcium stored in them properly. After tissue injury or surgery, vitamin A is needed for the repair of the tissues and to help protect the tissues from infection.
Normal levels of vitamin A are required in order to reproduce: female reproductive cycles depend on adequate amounts of serum vitamin A, and male sperm also needs vitamin A to be healthy. Vitamin A is also needed for the proper development of the placenta, as well as for the development of a healthy baby. A deficiency in vitamin A during pregnancy may lead to different abnormalities in the fetus. Those abnormalities can affect almost every organ system because vitamin A plays such a fundamental role in cell growth and maintenance of almost all cell types.
Vitamin A stimulates the growth of the base layer of the skin cells. It supports cell differentiation (knowing what type of cell to become as cells mature) and gives the cells their structural integrity. It does this for the external skin cells as well as for the body’s inner skin – the mucous membrane linings of the nose, eyes intestinal tract, respiratory lining, and bladder. Thus, it also helps protect these areas from cancer cell development. By moisturizing the mucous lining cells (which helps proper secretion) and by maintaining their structural integrity, vitamin A helps the body fight off infectious agents and environmental pollutants.
When there isn’t enough vitamin A, epithelial cells lose their integrity. This may cause the skin to become scaly and hard, and mucus secretion to be suppressed throughout the gastrointestinal tract
Vitamin A helps protect the body from the irritating effects of free radicals by neutralizing them. The antioxidant properties of vitamin A help protect the body from the irritating effects of smoke, air pollution, chemical exposure, and may also be helpful in preventing health problems like ulcers and atherosclerosis.
Immune function support and cancer risk protection.
In its preformed form (retinol) vitamin A has been shown to optimize the function of white blood cells, to enhance the recognition of food antigens by antibodies, and also to block the activity of certain viruses. The beta-carotene form of vitamin A has also been shown to enhance immune system function. The immune system requires adequate amounts of vitamin A for proper functioning. Vitamin A deficiency is directly linked to susceptibility to infections.
Vitamin A is necessary for the health and protection of epithelial tissue and mucous membranes, for eyesight, growth, bones, teeth, hair and skin.
Even though vitamin A deficiency is not so common, some people are more likely to have inadequate intakes.
People with diabetes and low thyroid activity, for example, do not easily convert beta-carotene to vitamin A.
As a fat-soluble vitamin, A needs fat to emulsify. Therefore, people with low liver/gall bladder functions or pancreatic insufficiency tend to be deficient in this vitamin. NOTE: More than 80% of people with cystic fibrosis have pancreatic insufficiency, and therefore a higher risk of vitamin A deficiency.
Pregnant women need extra vitamin A for fetal growth and to support their own metabolism. In women with vitamin A deficiency, the vitamin A content of breast milk is not sufficient to maintain adequate vitamin A stores in infants who are exclusively breastfed.
People, especially children, with Crohn’s disease and ulcerative colitis have a higher risk of deficiency, as well as children and adults with newly diagnosed celiac disease.
People with poor dietary habits, particularly those consuming high amounts of polyunsaturated fatty acids (PUFAs), have a higher risk of developing a deficiency.
What are the possible signs of vitamin A deficiency?
One of the first signs of vitamin A deficiency is night blindness, or the inability to see in low light or darkness. With a deficiency in vitamin A, you may develop general problems with eye tissue, impaired vision, irritated, reddened, or dry eyes, and eyes that get tired easily. Severe deficiency may lead to corneal ulcer development. Vitamin A deficiency is also one of the top causes of preventable blindness in children.
Chronic vitamin A deficiency has also been linked to abnormal lung development, respiratory diseases (such as pneumonia), and an increased risk of anemia.
Chronic vitamin A and beta-carotene deficiencies may decrease our protection against infections (particularly measles and infection-associated diarrhea).
Depletion of vitamin A reduces both T lymphocyte (cellular immunity) and B lymphocyte (antibody production) responses. In severe deficiency cases, atrophy of the thymus and spleen may develop, as well as a reduction in the number of circulating lymphocytes.
In addition to the lowered immune function and increased infection rate, periodontal disease, kidney stone formation, and ear problems may occur more frequently.
Vitamin A and beta-carotene deficiencies have been associated with an increased risk of some cancers as well as autoimmune diseases such as alopecia areata, multiple sclerosis, and autoimmune hepatitis.
Vitamin A deficiency also affects the skin. A good sign of that is dry bumpy skin, especially in the back of the arms. A deficiency may cause decreased skin tone, rapid aging of the skin, blemishes, acne, or boils.
Dry hair is a good sign of low vitamin A. Dandruff is also more likely to develop because of the loss of scalp skin moisture.
Vitamin A deficiency may lead to bone softness and abnormal menstruation.
Fatigue and insomnia are also possible, as are decreased appetite and some loss of smell and taste.
To sum it up, these are some of the possible signs of vitamin A deficiency:
- Dry or rough skin
- Dry hair
- Hard little bumps around elbows or on the back of upper arms
- Poor night vision; night blindness
- Eyes sensitive to bright light
- Increased susceptibility to (respiratory) infections
- Eyes have difficulty adjusting when entering a dark room
- Weak tooth enamel
What should you do if you suspect you may be deficient in vitamin A?
Test, don’t guess!
Consult with your doctor or healthcare provider first, and have your vitamin A levels tested. If you are deficient, you may need to change your diet and, if prescribed by your doctor, supplement accordingly to fix it.