Fat Soluble Vitamin Series, Vitamin A
Vitamins are among the micronutrients that are essential for a healthy body. They are divided into two major groups; the water-soluble vitamins and the fat-soluble vitamins. Fat-soluble vitamins consist of Vitamins A, D, E as well as K. Our bodies need to replace the water soluble vitamins on a regular basis but this is not the case for the fat-soluble vitamins, as they are usually stored in the fatty tissues and the liver in our bodies. Additionally, their elimination from the body is relatively slower compared to the other group of vitamins.
Vitamin A is a vital micronutrient for our bodies since it aids in the maintenance of a healthy vision, the growth of body cells and it is also good for our immune system due to its antioxidant properties just to mention a few of its key roles. To achieve all this, its actions are complemented by range of other micronutrients namely vitamin K2, D, magnesium as well as zinc.
Retinoid and Carotenoid forms of Vitamin A
Vitamin A is usually an umbrella term for a group of nutrients which can be majorly divided into two categories: the retinoids and the previtamin forms, carotenoids.
Retinoid or retinal is the biologically active form of vitamin A that our bodies can make use of. You can get it from animal sources by consuming food stuffs such liver and eggs just to mention a few.
Carotenoids are the pre-vitamin A form that are usually obtained from plant sources. They have to be converted to the active form in order for our bodies to use them, a function that normal and healthy individuals can only achieve. The enzyme that facilitates this conversion is beta-carotene-15, 15’-dioxygenase and it is usually expressed in the liver as well as the intestinal epithelium.
Absorption of Fat-soluble vitamins
The two groups of vitamins are absorbed differently by our bodies. As the name suggests, fat-soluble vitamins are usually soluble in fats, or technically speaking lipids. For this reason their absorption is normally done with the help of fat globules referred to as chylomicrons. Chylomicrons are able to gain entrance into our lymphatic systems in the small intestines and thereafter into our body’s general circulation.
Since they are usually stored in fatty tissues and the liver, you risk having an excess of these group of vitamins, a state of hypervitaminosis if you consume them in larger quantities than what is recommended. The overdose state manifests in a number of symptoms. On the other hand, anything that will interfere with their absorption via the small intestines will automatically lead to their deficiency once the body stores are depleted.
Food Sources for Vitamin A
If you are a great consumer of most of the plant and animal dishes you might just be taking adequate amounts of vitamin A. Retinoids are majorly obtained from animal sources of vitamin A while eating plants rich in vitamin A will be providing you with the previtamin form of vitamin A.
Animal sources of Vitamin A:
- Dairy products; cheese
- Oily fish
Plant sources of vitamin A:
- Fruits, the orange-coloured ones; mango, papaya
- Vegetables, the dark green ones; spinach, red pepper
Recommended Daily Amount (RDA) of Vitamin A
Below are the Recommended Daily Amounts of Vitamin A, set by the Food Standards Agency in the UK. The Recommend Daily Allowances (RDA) of Vitamin A, set by the National Institutes of Health in the US, are slightly higher.
- Adult males (age 15 and over) 700 micrograms/day
- Adult females (age 15 and over) 600 micrograms/day
- During pregnancy 700 micrograms/day
- During breastfeeding 950 micrograms/day
Provitamin A carotenoids and preformed vitamin A retinols are not nutritionally equivalent. One international unit (IU) of retinol, for example, is not the same as one IU of beta-carotene from food. Similarly, one IU of beta-carotene from food is not the same as one IU of beta-carotene from a vitamin supplement. The concept of retinol activity equivalents (RAE) was introduced to more easily compare the forms of vitamin A.
Retinol activity equivalents are as follows:
- 1 IU retinol (preformed vitamin A) = 0.3 mcg RAE
- 1 IU beta-carotene from dietary supplements = 0.15 mcg RAE
- 1 IU beta-carotene from food = 0.05 mcg RAE
- 1 IU alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE
1000 IU preformed vitamin A as a food or supplement = 2000 IU beta-carotene from supplements = 6000 IU beta-carotene from foods = 12000 IU alpha-carotene or beta-cryptoxanthin from foods
It is necessary to know the source of the vitamin A - whether it is preformed vitamin A, a carotenoid from food, or a carotenoid from a supplement, in order to understand vitamin A intake, assess adequacy of vitamin A intake and determine if vitamin A intake is adequate, or possibly even excessive.
Vitamin A Deficiency symptoms and signs
There are consequences of taking inadequate amounts of vitamin A and this usually manifests by one having a number of symptoms and signs. Since this vitamin is stored in the liver and in fatty tissues, it might take up to 2 years for the symptoms and signs to become evident. These symptoms are related to the vital roles played by vitamin A in our bodies, they include:
- night blindness
- dry and rough skin
- reduced resistance to infections, especially respiratory infections
- impaired development of the teeth
- a relatively slower growth of bone
Xerophthalmia is a term that is used in reference to vitamin A deficiency since most of the signs and symptoms affect the ocular, eye region especially the cornea and the conjunctiva.
Some individuals are more vulnerable (compared to the general population) to having a deficiency of vitamin A, these are:
Smokers and alcoholics since the consumption of these interferes with the intestinal absorption of lipids, of which fat-soluble vitamins are a part of. Additionally chronic alcoholism could result in liver damage which is a key store of the vitamin.
Those with Coeliac disease and Crohn’s disease; for the former there is a deficiency of the enzyme necessary in the conversion of beta carotene to the retinoid form while the intestinal walls of those with the latter are incapable of absorbing or digesting food due to the presence of huge lesions.
Those with Cystic fibrosis; they are deficiency of the enzymes needed in the absorption of lipids due to a dysfunctional pancreas
Individuals with Liver Cirrhosis, these individuals usually have an impaired flow of bile which is vital for the absorption of lipids in the small intestines. Additionally, the liver is also a major storage organ for vitamin A and its damage hugely impacts on the body stores of the vitamin.
Notable Health Benefits of Vitamin A
Maintenance of a Healthy Vision
Rhodopsin molecule, quite key in vision, has vitamin A as a key component. This molecule is usually activated as light is shone on the retina which results in it sending a signal to your brain which ultimately results in vision. Plant sources normally provide the body with beta carotene which hugely prevents us from having macular degeneration, which is a key reason for blindness as one ages.
Several studies are in support of this role of vitamin A in maintenance of a healthy vision. A study that was sponsored by the National Eye Institute proved that those who took daily amounts of this vitamin with its complement micronutrients were reported to have relatively reduced chances of having age-related degeneration of the macular. Some other studies poised vitamin A as an effective treatment of dry eyes and what is more is that it is as effective as the comparatively expensive eye drops.
Helpful in Skin care & cell growth
This essential micronutrient is quite key in the process of wound healing and in supporting a re-growth of our skins. It has been proven to internally and externally support our skin cells and its antioxidant properties that make it potent in fighting skin cancer. On a microbiological level, vitamin A is essential in the formation of glycoproteins, basically a combination of protein and sugar which is needed for binding cells.
Studies have shown that a deficiency of vitamin A leads to one having a rough and dry skin resulting in an undesirable complexion. There exists studies that recommend vitamin A as an effective treatment of acne and as a maintenance of a healthy skin.
It’s an integral complement to our immune system
Vitamin A has been hailed as a key immune system booting vitamin since most of the functions of this system are hinged on its availability in adequate amounts. This fat-soluble vitamin is responsible for regulating genes involved in generation of our immune responses. This explains the vital role of vitamin A in fighting diseases such as cancer as well as the autoimmune conditions besides being quite effective in preventing occurrence of common conditions such as common cold.
Acting as an antioxidant it also boosts our immune system in the clearance of free oxygen radicals which can be toxic to our body cells. In support of the plausible role of vitamin A in our immune system, a study carried out in London proved that vitamin A supplements resulted in a marked reduction in child mortality in less fortunate group of members of the society. These same studies also confirmed that a deficiency of this vitamin is associated with a higher occurrence of common infections such as measles and diarrhoea. Last but not least, a study conducted by the Columbian health-related social security system showed that the issuance of supplements resulted in a commendable reduction in medical costs estimated at about $350 million.
Vitamin A is a fat-soluble vitamin that is quite essential in the maintenance of healthy vision, skin and it as a great boosting vitamin to our immune system. It is available in two forms, retinoid majorly derived from animals and carotenoids found in the plant sources. By taking an adequate diet rich in fruits, vegetables and the relevant animal products, notably beef liver you will be adequately covered as far as vitamin A is concerned. Some conditions which interfere with the absorption or storage of this vitamin could result in its deficiency, this could be dealt with consumption of foods rich in the retinoids or taking vitamin A supplements.