Compiled & reviewed by
Dr.Sanjana.v.bBhms.Dbrm,Cdn

Vitamin A

  Vitamin A is a fat soluble vitamin which is abundantly found in many vegetables and fruits. Vitamin A is an important micronutrient for immune function, cellular communication, growth and development.

The two main forms of vitamin A in the human diet are preformed vitamin A (retinol, retinyl esters), and pro vitamin A carotenoids such as beta-carotene that are converted to retinol.

Preformed vitamin A comes from animal products, fortified foods, and vitamin supplements.

Carotenoids are found naturally in plant foods. Carotenoids are turned into vitamin A by your body. They are found in fruits, vegetables, and other plant-based products.

 There are other types of carotenoids found in food that are not converted to vitamin A but have health-promoting properties; these include lycopene, lutein, and zeaxanthin.

Functions of vitamin A in your body 

·       Vitamin A supports cell growth and differentiation, playing a crucial role in the normal formation and maintenance of the heart, lungs, eyes, and other organs.

·       Vitamin A is also vital for vision or eyesight as an essential component of rhodopsin, the light-sensitive protein in the retina that responds to light entering the eye.

·       Vitamin A helps to boost your immunity

·       It is an effective antioxidant

·       Vitamin A protects mucosal linings of your body such as nose,gut etc.

·       It is essential for the growth of healthy skin and hair.     

      Retinoic acid [ a compound of vitamin A] influences the functioning of the hair cycle , wound healing, and melanocyte stem cells. Retinoic acid also influences melanocyte differentiation on skin. However both deficiency and excess of vitamin A has adverse effects on skin and hair. Excessive vitamin A intake may result in hair loss and reduced sebaceous gland function.

Sources of vitamin A:

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

 Pro vitamin A carotenoids are plant pigments that the body converts into vitamin A in the intestine. The main pro vitamin A carotenoids are beta-carotene, alpha-carotene, and beta-cryptoxanthin. Sources of provitamin A are leafy green vegetables, orange and yellow vegetables, tomato products, fruits, and some vegetable oils.

Common sources of vitamin A include:

·       Leafy green vegetables (kale, spinach, broccoli),

·       orange and yellow vegetables (carrots, sweet potatoes, pumpkin ,winter squash, summer squash)

·       Tomatoes

·       Red bell pepper

·       Cantaloupe

·       mango

·       Beef liver

·       Fish oils

·       Milk

·       Eggs

How to assess deficiency of vitamin A?

In clinical practice, plasma retinol levels alone can be used to evaluate significant deficiency.A serum or plasma retinol concentration of 20 mcg/dL or less indicates moderate vitamin A deficiency, and a level of 10 mcg/dL or less is considered an indicator of severe vitamin A deficiency.

However plasma retinol levels are not often accurate. Even if there is chronic infection and vitamin A level is lowered, the retinol level in plasma will remain normal until the liver stores of vitamin A is depleted.

In clinical studies, specialized research laboratories can measure liver vitamin A reserves indirectly using isotope-dilution or dose-response methods. In common clinical practice these tests are not used regularly as vitamin A deficiency is rare in most of the countries.

How much vitamin A is needed per day?

Recommended Dietary Allowance (RDA)

 Average daily level of intake sufficient to meet the nutrient requirements.

For men it is 900 mcg RAE [equivalent to 3,000 IU) and

For  women 700 mcg RAE (equivalent to 2,333 IU).

Impact of vitamin A deficiency

  The most common clinical sign of vitamin A deficiency is xerophthalmia. The first sign is night blindness, or the inability to see in low light or darkness as a result of low rhodopsin levels in the retina.

 Xerophthalmia also affects the cornea and can eventually lead to permanent blindness. Vitamin A deficiency is one of the top causes of preventable blindness in children .

 Chronic vitamin A deficiency has also been associated with abnormal lung development, respiratory diseases (such as pneumonia), and an increased risk of anemia and death.

 Chronic vitamin A deficiency is associated with increased severity of infections and increased death rate consequent to that.

Who are at risk of vitamin A deficiency or inadequacy?

·       Premature infants- Preterm infants with vitamin A deficiency have a higher risk of eye and chronic lung diseases

·       Infants, children, and pregnant and lactating women in underdeveloped countries.

·       People with cystic fibrosis disease have pancreatic insufficiency, which increases their risk of vitamin A deficiency due to difficulty in absorbing fat. Vitamin  A is a fat soluble vitamin &hence deficiency occurs.

What do the research studies say about the link between cancer & excessive vitamin A intake?

 Several studies have shown that higher dietary intakes of retinol, carotenoids & vitamin A rich fruits and vegetables [i.e. from natural sources] are associated with a lower risk of lung cancer, non-Hodgkin lymphoma, pancreatic cancer, oral cavity cancer, laryngeal cancer, esophageal cancer, ovarian cancer, glioma, and bladder cancer.

Some clinical trial evidence suggests that supplemental vitamin A might reduce the risk of certain cancers but increase the risk of other forms of cancer, heart attacks etc. Hence unnecessary or excessive supplementation of vitamin A is not recommended.

But adequate intake of natural food sources of vitamin A is recommended for better health. Supplementation is indicated only in case of severe deficiency symptoms and diseases necessitating supplementation.

REFERENCES [Research links]

1.    https://www.hsph.harvard.edu/nutritionsource/vitamin-a/

2.     https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/

3.    https://ods.od.nih.gov/factsheets/VitaminA-Consumer/#:~:text=Vitamin%20A%20is%20important%20for,fruits%20and%20vegetables%20their%20color.

4.    https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-a/

5.    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9324272/