Vitamin A: What Role In Immune Function?

At the top of a group of fat-soluble retinoids and encompassing retinol, retinal and retinyl esters, vitamin A, also called retinol, is involved in immune function, vision, reproduction, and cellular communication. In the healthy diet, this super important vitamin is available in two forms. Our article will zoom in on the necessary intake of vitamin A and food sources.

Vitamin A: essential for growth and health

Namely, retinol is essential for vision as a main component of rhodopsin which is a light absorbing protein in retinal receptors and because it supports the differentiation and normal function of conjunctival membranes and cornea. Vitamin A also supports cell growth and differentiation, playing an essential role in the normal formation and maintenance of the heart, lungs, kidneys and other organs.

May reduce the risk of certain cancers

When abnormal cells start to grow or divide in an uncontrolled manner, the risk of cancer is very high. In observational studies, consuming larger amounts of vitamin A in the form of beta-carotene has been associated with a decreased risk of certain types of cancer, including Hodgkin's lymphoma, as well as cervical cancer. uterus, lung and bladder.

Yet while high intakes from plant foods have been linked to a reduced risk of cancer, foods of animal origin that contain active forms of vitamin A are not related in the same way.

Likewise, the element's supplements have not shown the same beneficial effects. At this time, the relationship between the levels in your body and the risk of cancer is still not fully investigated.

Prevent eye problems

First and foremost, vitamin A is essential for preserving your eyesight. It converts the light that hits the eye into an electrical signal which is then sent to the brain. In fact, one of the first symptoms of vitamin A deficiency can be the development of eye diseases, such as nyctalopia. This discomfort occurs in people with a deficiency of this major component of the rhodopsin pigment. It, on the other hand, is located in the retina of the eye and is extremely sensitive to light. Therefore, sufferers can still see normally during the day, but have reduced vision in the dark as their eyes have difficulty picking up light at lower levels.

For a healthy immune system

The body defends itself in a natural way thanks to retinol by creating mucous barriers in the eyes, lungs, intestines and genitals. They are real traps for bacteria and other infectious agents. Retinol is also involved in the production and function of white blood cells which in turn help capture and remove bacteria and pathogens from the bloodstream.

In short, susceptibility to infections increases, recovery from illness is delayed and the risk of dying from certain plagues such as measles and malaria is potential.

Benefits for the skin

Almost everyone, through their teenage years, has felt embarrassed by acne - a chronic inflammatory skin disorder. Although pimples are physically harmless, acne can have a serious effect on people's mental health and lead to low self-esteem, anxiety, and depression. As the role of retinol in the development and treatment of acne remains unclear, it is speculated that a deficiency may increase the risk of developing acne, as it causes overproduction of the keratin protein in your hair follicles and as a result, blockages.

Bone health

Primarily, the key nutrients needed to maintain healthy bones as you age are supplements and foods high in protein, calcium, and vitamin D.

However, consuming enough vitamin A is also necessary for proper bone growth and development, while on the contrary, a deficiency of this vitamin is linked to a higher risk of bone fractures.

Impact on reproduction

When a pregnant woman takes vitamin A regularly, she is aware that the development of her unborn child depends to a great extent on it, especially the skeleton, nervous system, heart, kidneys, eyes, lungs and pancreas..

Existing forms of retinol

Two forms of vitamin A are available in the human diet: the preformed form (retinol and its esterified form, retinyl ester) and the provitamin A carotenoids. The preformed form is found in foods of animal origin, including dairy products, fish and meat. Beta-carotene is the most important provitamin A carotenoid and the others are alpha-carotene and beta-cryptoxanthin. The body converts these plant pigments into vitamin A. As a result, they must be metabolized intracellularly into retinal and retinoic acid, the active forms of vitamin A, to support its important biological functions. Other carotenoids in foods, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A.

Vitamin A: deficiencies and consequences

Primarily, vitamin A deficiency is rare in the United States and Europe, while it is common in many developing countries. This is due to the residents' limited access to foods containing preformed vitamin A. Due to poverty and famine, these peoples generally do not consume products from animal sources that contain beta-carotene. Therefore, in these countries, low vitamin A intake is most strongly associated with health consequences during times of high nutritional demand, such as infancy, childhood, pregnancy and breastfeeding.

Groups at risk

During infancy

In developing countries, vitamin A deficiency usually begins during infant age, when newborns do not receive enough colostrum or breast milk. As a result, chronic diarrhea leads to excessive loss of vitamin A in young children and vice versa, vitamin A deficiency increases the risk of diarrhea.

The most common symptom of this deficit is xerophthalmia, the first signs of which are night blindness or the inability to see in the dark. This discomfort is also due to a low level of iron which in turn can lead to anemia. Therefore, the risk of death from infections (especially diarrhea and measles) increases even before xerophthalmia begins.

Pregnant and lactating women in developing countries

According to statistics, around 10 million pregnant women need vitamin A supplementation for fetal growth, tissue maintenance and to support their own metabolism.

In addition, there is an increase in maternal and infant morbidity and mortality in pregnant and breastfeeding women, an increased risk of anemia and a slowdown in infant growth and development.

Premature infants

In principle, all infants with malabsorption disorders lack vitamin A, but those who are premature do not have adequate liver reserves at birth. At the same time, their plasma retinol concentrations often remain low throughout the first year of life. This inevitably leads to an increased risk of eye, chronic lung and gastrointestinal diseases.

People with cystic fibrosis

Most people with cystic fibrosis suffer from pancreatic insufficiency, which increases their retinol deficiency, due to the difficulty in absorbing fat. Several cross-sectional studies have shown that 15% to 40% of patients with cystic fibrosis lack this element. However, improved pancreatic replacement therapies, better nutrition, and calorie supplements help this risk group overcome the deficit.

Deposits of the element in the body

Levels of retinol and carotenoids are usually measured in plasma, and plasma retinol levels are useful for assessing vitamin A deficiency. However, their value for assessing marginal element status is limited because they do not decrease as long as the levels of the vitamin in the liver are almost not exhausted. Liver stores can be measured indirectly by the relative dose-response test, in which plasma retinol levels are measured before and after administration of a small amount. An increase in plasma retinol level of at least 20% indicates an insufficient level of the vitamin. Most of the vitamin stores in the body are stored in the liver as retinyl esters.

Sufficient necessary intake for the human organism

In general, recommendations for intake of the element and other nutrients are provided in the Dietary Reference Intakes (ANR / ANC), developed by the Food and Nutrition Board (FNB) of the Institute of Medicine of the National Academies. (former National Academy of Sciences). Reference Food Ingredients (IAR), is the general term for a set of reference values used to plan and assess the nutrient intakes of healthy people. These values vary by age and sex.

For healthy people

To meet the nutritional needs of almost all healthy people, the daily intake should be 97% to 98%. This value is often used to plan adequate diets for individuals.

Guarantee nutritional adequacy

In this case, it is an adequate intake which is assumed to ensure nutritional adequacy, established when there is insufficient evidence to develop a recommended dietary allowance (RDA).

Estimated average requirement (EAR)

This is an average daily level of intake estimated to meet the needs of 50% of healthy individuals. It is generally used to assess the nutritional intakes of groups of people and to plan adequate diets for them. It may also be used to assess the nutritional intake of individuals.

Tolerable upper intake level or tolerable upper intake (UL)

Namely, the maximum daily intake is unlikely to cause adverse health effects. However, the Reference Daily Intakes (RDI) are given in the form of activity equivalents of retinol (RAE) to take into account its different bioactivities and the carotenoids of provitamin A. Thus, they are all converted by the body. in retinol.

Excessive consumption

Stored in the body in large amounts, this fat soluble vitamin can lead to toxic levels, resulting in nausea, dizziness, headaches, pain and even death. This can happen rarely and carries no risk if it is in the vegetable form. Pay attention to other medications taken at the same time and consult your GP, if necessary.

Sources of vitamin A

It should be noted above all that in the form of retinol, this element exists in mammals and as provitamin A, alias beta carotene, is found in plants.

Meats: turkey, beef, chicken

Vegetables: sweet potato, carrots (juiced or cooked), pumpkin (canned), boiled spinach, cabbage, beetroot, turnip, lettuce, dandelion leaves, red pepper, tomato (the juice)

Fruits: melon

Fish: Atlantic herring