Vitamin A benefits are very important to maintain good health. Vitamin A is a fat soluble vitamin. What does it mean? You have water soluble vitamins and fat soluble vitamins. Fat soluble vitamins have the ability to travel through fats and to be stored in fat longer, it has the ability to go through cell walls because layers around cells are made of fat.
Fat soluble vitamins have the capacity to go inside the cell faster while water soluble vitamins take longer. Fat soluble vitamins can affect the deep parts of the cell, the alteration of the DNA.
Vitamin A is well known for its effect in the eyes, specially when there is a deficiency in third world countries and there is blindness it is probably caused by vitamin A deficiency. Apart from the eyes, vitamin A is involved in the body’s immune mechanism, skin and mucous membranes , cell growth and differentiation especially in the function and health of the heart, lung, kidney, and reproduction.
Vitamin A gives support to the eye, to the skin, to the immune system, to the inner skin , around your nasal passages and sinuses, protect the tissues of the digestive system including the mouth, esophagus, stomach, small intestine and large intestine. If you have sleep apnea or problems that have to do with the inner skin in your throat, infections, sinusitis, frequent colds, asthma, gum disease, that could be vitamin A deficiency.
There Are Two forms of vitamin A In The Human Diet
1-Preformed vitamin A : Retinol and its esterified form, Retinyl ester Foods from animal sources: dairy products, fish, and meat ,
2-Provitamin A carotenoid: Beta-carotene, alpha carotene, Beta cryptoxanthin. The body converts these plant pigments into Retinol. Both provitamin A and preformed vitamin A must be metabolized intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin’s important biological functions [2,3]. Other carotenoids found in food, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A.
The various forms of vitamin A are solubilized into micelles in the intestinal lumen and absorbed by duodenal mucosal cells . Both Retinyl esters and provitamin A carotenoids are converted to retinol, which is oxidized to retinal and then to retinoic acid [2]. Most of the body’s vitamin A is stored in the liver in the form of Retinyl esters.
Diferent types of Vitamin A
1- Retinol Palmitate: In animal sources Liver, eggs yolks, fish, cheese
2- Betacaroteno: In plant sources: Carrot, spinach, sweetpotato
3- Retinyl Palmitate: Synthetic. In supplements and prescription form to treat vitamin A deficiency
Retinol Palmitate Retinyl Palmitate
Known as Vitamin A Known as Vitamin A Palmitate
In animal sources Made in the lab from
Alcohol Ester
C20H3O C36H6O2
Unstable, easily oxidized Stable, not easily oxidized and
and degradable and degradable
Used in the body by the Used as a supplement to treat
Photoreceptors cell of eyes, Vit. A deficiency in people.
Immune system, skin and
Mucus membranes
Formation involves the enzyme Formation involves a reaction
Beta carotene 15,15’oxygenase of Palmitic Acid with Retinol
Retinol and carotenoid levels are typically measured in plasma
Plasma retinol levels are useful for assessing vitamin A inadequacy. However, their value for assessing marginal vitamin A status is limited because they do not decline until vitamin A levels in the liver are almost depleted [3]. Liver vitamin A reserves can be measured indirectly through the relative dose-response test, in which plasma retinol levels are measured before and after the administration of a small amount of vitamin A [5]. A plasma retinol level increase of at least 20% indicates an inadequate vitamin A level [3,5,6]. For clinical practice purposes, plasma retinol levels alone are sufficient for documenting significant deficiency.
A plasma retinol concentration lower than 0.70 micromoles/L (or 20 micrograms [mcg]/dL) reflects vitamin A inadequacy in a population, and concentrations of 0.70–1.05 micromoles/L could be marginal in some people [5]. In some studies, high plasma or serum concentrations of some provitamin A carotenoids have been associated with a lower risk of various health outcomes, but these studies have not definitively demonstrated that this relationship is causal.
Recommended Intakes
-
- RDA: The Recommended Dietary Allowance for adults 19 years and older is 900 mcg RAE for men (equivalent to 3,000 IU) and 700 mcg RAE for women (equivalent to 2,333 IU).
UL: The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for vitamin A from retinol is 3,000 micrograms of preformed vitamin A.
Foods Rich In Vitamin A
Vitamin A is in cod liver oil, liver, butter, eggs specially the yolk, cheese, fish. That is the active form of vitamin A called Retinol. It is true that kale, spinach, carrot, sweet potato, greens, papaya, pumpkin, pepper have a lot of vitamin A in its pre-vitamin A form. It has to be converted into an active form, that conversion takes place in certain parts of your body and only in certain percentages, if you are lacking it you can get only 4-6% conversion. If you are getting 100 mg of vitamin A from kelp, you are only converting 4-6%. Just because you are eating kelp does not mean that you are getting enough vitamin A, especially if you are not consuming enough animal products that have vitamin A. That is some interesting information.
Beta carotene is derived from carrots, one molecule of beta carotene it produces two molecules of active vitamin A
Vitamin A Content of Selected Foods [9]
Food Micrograms (mcg)
RAE per serving Percent DV*
Beef liver, pan fried, 3 ounces 6,582 731
Sweet potato, baked in skin, 1 whole 1,403 156
Spinach, frozen, boiled, ½ cup 573 64
Pumpkin pie, commercially prepared, 1 piece 488 54
Carrots, raw, ½ cup 459 51
Ice cream, French vanilla, soft serve, 1 cup 278 31
Cheese, ricotta, part skim, 1 cup 263 29
Herring, Atlantic, pickled, 3 ounces 219 24
Milk, fat free or skim,
with added vitamin A and vitamin D, 1 cup 149 17
Cantaloupe, raw, ½ cup 135 15
Peppers, sweet, red, raw, ½ cup 117 13
Mangos, raw, 1 whole 112 12
Vitamin A Content of Selected Foods [9]
Food Micrograms (mcg)
RAE per serving Percent DV*
Breakfast cereals,
fortified with 10% of the DV for vitamin A,
1 serving 90 10
Egg, hard boiled, 1 large 75 8
Black-eyed peas (cowpeas), boiled, 1 cup 66 7
Apricots, dried, sulfured, 10 halves 63 7
Broccoli, boiled, ½ cup 60 7
Salmon, sockeye, cooked, 3 ounces 59 7
Tomato juice, canned, ¾ cup 42 5
Yogurt, plain, low fat, 1 cup 32 4
Vitamin A Content of Selected Foods [9]
Food Micrograms (mcg)
RAE per serving Percent DV*
Tuna, light, canned in oil,
drained solids, 3 ounces 20 2
Baked beans, canned,
plain or vegetarian, 1 cup 13 1
Summer squash, all varieties,
boiled, ½ cup 10 1
Chicken, breast meat and skin,
roasted, ½ breast 5 1
Pistachio nuts, dry roasted, 1 ounce 4 0
Vitamin A Test
You can measure the levels of vitamin A with the Retinol Test that can be requested by a Health Professional.
- Plasma concentrations of vitamin A can be measured by Retinol Test and the normal values range from 15 to 60 micrograms per deciliter (mcg/dL) or 0.52 to 2.09 micromoles per liter (micromol/L).
-
REFERENCE VALUES
- 0-6 years: 11.3-64.7 mcg/dL
- 7-12 years: 12.8-81.2 mcg/dL
- 13-17 years: 14.4-97.7 mcg/dL
- > or =18 years: 32.5-78.0 mcg/dL
-
INTERPRETATION
- The World Health Organization recommendations supplementation when vitamin A levels fall below 20.0 mcg/dL.
- Severe deficiency is indicated at levels less than 10.0 mcg/dL.
- Vitamin A values above 120.0 mcg/dL suggest hypervitaminosis A and associated toxicity.
What causes vitamin A deficiency?
Could be because you are not consuming enough of animal products that have vitamin A of you are not converting the vitamin A from vegetable products, but most likely you are consuming enough vitamin A. But the deficiency comes from the ability to convert and this has to do with your gut, your digestive system is damage or you have history of talking antibiotics or leaky gut for gluten or other food sensitivity you can not convert it and your skin is going to dry out, you hair is going to dry out, eyes dry. So you start to manifest vitamin A deficiency.
Another cause of vitamin A deficiency is due to lack of bile from the gallbladder, because the bile helps to break down fats and vitamin A is a lipid soluble vitamin so your body can start utilizing them. So if you do not have a gallbladder you probably do not have enough bile to absorb vitamin A and you have to take some bile as a supplement. The symptoms of not having enough bile are: bloating, burping, boulching, right shoulder pain and constipation. It could be because your stomach is not acid enough so you have heartburn, because in order to release enough bile, you need a very strong stomach.
Excessive Amounts of Vitamin A Can Cause Toxicity
The recommended amount of vitamin A for adults is 3000IU. Toxicity is caused by eating 10 times this amount depending of you bodyweight and tolerance. People in the artic avoid eating polar bear liver because is toxic but there have been reference of toxicity since 1596. The last well known case of explorers that were lost in the artic and died for eating polar bear liver was in 1914. They ate bear liver and were intoxicated because the quantity of vitamin A in bear liver is too much for human consumption. The polar bears eat seals and their liver has a enormous amounts of vitamin A, around 9’000,000 IU, this will kill 300 adults. This is why eating bear liver is extremely dangerous for humans.
By other hand, cows are herbivores and they do not have dangerous amounts of vitamin A in their liver and humans can eat beef liver once a week. Chicken and duck liver is safe too, they have small amounts of vitamin A.
Vegetarian sources of vitamin A is safe too because humans only absorbe 4-25% of beta-carotene that is the vegetarian form of vitamin A.
The chemical form of vitamin A can be toxic if it is taken in big dosages more than the recommended amount. Among these is Retinyl Palmitate that is common in vitamin and supplements over the counter or the prescription forms used for acne and skin conditions. If you take too many supplements that contain vitamin A it could be a problem, this is why make sure to check the amount of vitamin A contain in your supplements.
The acute toxicity for vitamin A is called Hypervitaminosis A and is produced when very large amounts of vitamin A are consumed at once. The sign and symptoms are: irritability, drowsiness, nausea, abdominal pain, a feeling of pressure on the brain, vomiting, mouth ulcers, swelling of the bones.
When large amounts are of vitamin A, specially artificial vitamin A is consumed in longer period of times it is called Chronic Hypervitaminosis A. The sign and symptoms are: loss of appetite, bone pain, cracked corners of the mouth, blurry vision or other vision changes, dizziness, nausea and vomiting, sensitivity to sunlight, rough, dry, peeling, or itchy skin, jaundice, hair loss, confusion, respiratory infection, cracked fingernails.
Conclusion:
Vitamin A is a fat soluble vitamin that is stored in different tissues around the body specially in the liver. It is important for different functions and tissues in the body specially the eyes, the skin, the mucous membranes, the immunological system, respiratory system, heart, and reproductive system.
Vitamin A is available from variety of foods. The main animal sources of vitamin A are beef liver, eggs, cheese, fish. They have the form Retinol that is well absorbed. The vegetarian form is called beta carotene and is better absorbed when the vegetable is cooked. The main source of beta carotene are: pumpkin, sweet potato, carrots and spinach.
The Retinol Test by prescription is used to measure the levels of vitamin A.
There is vitamin A over the counter that can be used when there is vitamin A deficiency. Consult your health professional for more information.
References:
- https://www.hsph.harvard.edu/nutritionsource/vitamin-a/#:~:text=RDA%3A%20The%20Recommended%20Dietary%20Allowance,(equivalent%20to%202%2C333%20IU)
- https://www.sciencedirect.com/science/article/abs/pii/S0083672908602381?via%3Dihub
-https://pubmed.ncbi.nlm.nih.gov/16188508/ Low levels of carotenoids and retinol in involutional osteoporosis. Dario Maggio et al. Institute of Gerontology and Geriatrics, University of Perugia, Policlinico Monteluce, Via Brunamonti, 06124 Perugia, Italy. dariomaggio1@tin.it.Bone. Volume 38, Issue 2, February 2006, Pages 244-248. About the role of preform vitamin A and carotenoids in prevention of osteoporosis.
– https://pubmed.ncbi.nlm.nih.gov/25802864/ Atherosclerosis due to vitamin D deficiency
The takeaway
Eating a healthy diet with animal and vegetarian products could provide with the daily recommended amounts. If you want to know more or are concern with your vitamin A intake consult with your health provider. If you find this article informative please leave a comment in the comment section. Vitamin A benefits are essential to maintain optimal health.