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Vitamin A
Vitamin A | The essential fat-soluble vitamin
Vitamin A is a fat-soluble vitamin that is naturally present in many foods. Vitamin A is the name of a group of fat-soluble retinoids, which are primarily retinol and retinyl esters.

Vitamin A for health

Vitamin A is critical in the normal function and maintenance of the heart, lungs, eyes, and other organs. Vitamin A supports cell growth, development and differentiation, and vitamin A is essential for cellular communication. Vitamin A also plays a role in human reproduction. In addition, vitamin A is involved in immune function.

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Vitamin A for healthy eyes

  • Vitamin A is vital for maintaining normal and healthy eye and vision functions.

  • Vitamin A is critical for vision as an essential component of rhodopsin. Rhodopsin is a light-sensitive protein in the retina that responds to light entering the eye.

  • Vitamin A supports the normal function and maintenance of the conjunctival membranes and cornea.

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The Role of Vitamin A in Vision and Immune Function

Vitamin A is essential for the health of the retina, where it contributes to the conversion of light into a signal that can be sent to the brain. In terms of immune health, it plays a crucial role in maintaining the integrity and function of skin and mucosal cells, which form a barrier and are the body's first line of defense against infections.

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The two types of vitamin A | preformed vitamin A and provitamin A carotenoids

Two types of vitamin A: preformed vitamin A and provitamin A carotenoids

Two sources of vitamin A contained in the human diet are preformed vitamin A and provitamin A carotenoids.

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Preformed vitamin A is retinol and retinyl esters. Preformed vitamin A is found in foods from animal sources, including eggs, fish, dairy products, and animal organ meats.

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Provitamin A carotenoids are pigments in plants that give yellow, orange, and red fruits and vegetables their colour.

The main provitamin A carotenoids in the human diet that can be converted into vitamin A in human intestines are alpha-carotene, beta-carotene, and beta-cryptoxanthin.

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The nutritional food sources of vitamin A

Vitamin A is found naturally in many foods as the following:

  • Some types of fish, such as herring and salmon.

  • Animal organ meats such as the beef liver.

  • Green leafy vegetables and other green, orange, and yellow vegetables, such as spinach, carrots, broccoli, and sweet potatoes.

  • Dairy products, such as milk and cheese.

  • Fortified breakfast cereals

  • Eggs.

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The top foods of good sources of vitamin A

  • Beef liver

  • Sweet potatoes

  • Spinach

  • Pumpkin

  • Carrots

  • Herring fish

  • Milk with added vitamin A and vitamin D

  • Cantaloupe

  • Cheese

  • Red sweet peppers

  • Mangos

  • Eggs

  • Apricots

  • Broccoli

  • Salmon

  • Tomato juice

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Recommended Amounts

The recommended dietary intake of vitamin A is given as RDA (Recommended Dietary Allowance).

 

RDAs for vitamin A are given as retinol activity equivalents (RAE) to account for the different bio-activities of retinol and provitamin A carotenoids. All of the provitamin A carotenoids are converted by the body into retinol. One microgram of RAE is equivalent to one microgram of retinol, and one microgram of RAE is equivalent to two micrograms of supplemental beta-carotene.

 

The RDA for people 14 years and older is 900 micrograms of RAE and 700 micrograms of RAE for males and females, respectively.

The RDAs for females in pregnancy are 750 micrograms RAE and 770 micrograms RAE for teens (14-18 years) and women (19-50 years), respectively.

The RDAs for females in lactation are 1200 micrograms RAE and 1300 micrograms RAE for teens (14-18 years) and women (19-50 years), respectively.

 

Recommended Dietary Allowance (RDA):

What is RDA? RDA means Recommended Dietary Allowances; RDA is the daily nutritional sufficient nutrient level. RDA is the dietary intake value that represents what you need to take on a daily basis. RDA is the average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy individuals.

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The Recommended dietary allowances (RDAs) for vitamin A for all age groups people are listed in the following table.

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RDAs for vitamin A are given as retinol activity equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids. All of provitamin A carotenoids are converted by the body into retinol.

 

One microgram RAE is equivalent to one microgram retinol, two micrograms supplemental beta-carotene.

 

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Toxicity of Vitamin A

High intakes of some forms of vitamin A can be harmful.

There are health risks from excessive intake of vitamin A. Established upper intake levels (UL) for preformed vitamin A apply to both food and supplement intakes.

The daily upper limits (UL) for preformed vitamin A include intakes from all sources, food, beverages, and supplements. The levels do not apply to people taking vitamin A for medical reasons under a doctor's care.

The ULs for preformed vitamin A are 2800 micrograms for 14-18 years people and 3000 micrograms for people 19 years and older.

The ULs apply only to products from animal sources and supplements whose vitamin A comes entirely from retinol or its ester form (retinyl ester), such as retinyl palmitate. There are no upper limits for beta-carotene and other forms of provitamin A.

In some supplements, vitamin A consists partly or entirely of beta-carotene. In these cases, the percentage of retinol or retinyl ester in the supplement should be used to determine whether an individual’s vitamin A intake exceeds the UL.

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The daily upper limits for preformed vitamin A include intakes from all sources—food, beverages, and supplements—and are listed below. These levels do not apply to people taking vitamin A for medical reasons under a doctor's care. The ULs apply only to products from animal sources and supplements whose vitamin A comes entirely from retinol or its ester form (retinyl ester), such as retinyl palmitate. There are no upper limits for beta-carotene and other forms of provitamin A.In some supplements, the vitamin A consists partly or entirely of beta-carotene. In these cases, the percentage of retinol or retinyl ester in the supplement should be used to determine whether an individual’s vitamin A intake exceeds the UL. For instance, a supplement whose level indicates that the product contains 3000 mcg RAE vitamin A and that 60% of this vitamin A comes from beta-carotene, and 40% of vitamin A comes from retinol or retinyl ester, therefore, in this supplement, there is 1200 mcg RAE of preformed vitamin A (retinol and retinyl esters). This amount is above the UL for children from birth to eight years but below the UL for older children and adults.

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Vitamin A and Healthful Diets

 

Our nutritional needs should be met primarily through foods, because foods provide an array of nutrients and other components that benefit health. Foods contain vitamins, minerals, dietary fibre, and other nutrients that are beneficial for our health. In some situations and cases, fortified foods and dietary supplements are helpful when it is impossible to meet the needs for one or more nutrients.

 

A healthy eating pattern with good vitamin A intake is one that:

  • Includes a variety of vegetables, whole grains, fruits, milk and milk products and oils. Good nutritional sources of vitamin A include vegetables & fruits, and dairy products. Some brand ready-to-eat breakfast cereals are fortified with vitamin A; you need to check the nutrition label of cereal products.

  • Includes a variety of protein foods, including lean meats and poultry, seafood, eggs, legumes, beans and peas, nuts and seeds, and soy products. Beef liver has high amounts of vitamin A.

  • Limits foods and beverages higher in saturated fat, added sugars, and sodium.

  • Limits alcoholic beverages.

  • Stays within your daily calorie needs.

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References:

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