Vitamin A: Sources, Function, Benefits, & Consequences of Deficiency

Table of Contents

What is Vitamin A?

Vitamin ‘A’ is a fat-soluble vitamin. Vitamin A is an important micro-nutrient that is essential for different biological and metabolism functions.

There are two types of vitamin A that are found in the diet:

Preformed vitamin A (retinol and its esterified form, retinyl ester): found in animal products such as meat, fish, poultry, and dairy foods.
Provitamin A: found in plant-based foods such as fruits and vegetables. The most common type of pro-vitamin A is beta-carotene.

Most common form of preformed vitamin A and provitamin A is retinol and β-carotene respectively.

Now, let us know about the function, Recommended Dietary Allowance (RDA), symptoms and consequences of Vitamin A along with the high-risk groups for Vitamin A deficiency and of Vitamin A.

What are the Sources of Vitamin A?

Functions of Vitamin A:

Stimulate production and activity of white blood.
Help in remodeling the bone.
Help to maintain healthy endothelial cells
Regulate cell growth and division.
Provide immune defense and protects against infections.
Maintain hormonal system, reproduction and formation of new sperm cells.
Act as an antioxidant (mainly β-carotene) which neutralizes free radicals.

What is the Recommended Dietary Allowance (RDA) of Vitamin A?

Institute of Medicine lists the Recommended Dietary Allowances (RDA) of vitamin A in micrograms (mcg) of retinol activity equivalents (RAE) to account for different absorption rates of preformed vitamin A and provitamin A carotenoids.

According to Food and Drug Administration (FDA), as of July 2018 large companies will no longer list vitamin A as IU but as “mcg RAE.”

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).
Upper Intake Level (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.

Health Benefits of Vitamin A:

Boosts immunity
Reduces the risk of cancer
Improves eyesight
Helps to maintain healthy skin
Strengthens bones.
Helps to maintain healthy reproductive system.
Protects against heart disease and ageing.
Reduces the symptoms of ageing.
Supports bodily functions.
Helps to reduce the risk of urinary stones.

Symptoms of Vitamin A Deficiency:

Night blindness, dry eyes, and conjunctivitis.
Dry, flaky skin and other skin conditions.
Dry and sensitive mucous membranes.
Impaired immunity.
Fragile hair and nails that crack or split.
Reduced ability to hear, smell and taste.
Abnormal fetal development.
Weight loss.
Insomnia.
Fatigue.

Consequences of Vitamin A Deficiency:

Consequences of Mild Vitamin A deficiency:

Fatigue
Compromised immune system
Susceptibility to infections
Infertility

Consequences of Severe Vitamin A Deficiency:

Vitamin A Deficiency (VAD) is responsible for 1/4^th of global child mortality from measles, diarrhea and malaria and 1/5^th of all cause maternal mortality. Apart from this, other consequences of Vitamin A deficiency are:

Xerophthalmia, a severe dryness of the eye that can lead to blindness, if left untreated.
Nyctalopia or night blindness
Irregular patches on the white of the eyes
Dry skin or hair
Metaplasia
Epithelial differentiation
Compromised immunity

Consequences of Vitamin A Toxicity:

Nausea
Vomiting
Dry skin
Anorexia
Hyperirritability
Muscular weakness
Bone pain
Vision changes such as blurred sight
Sensitivity to bright light
Skeletal malformation, spontaneous fractures and internal hemorrhage (during chronic toxicity)

Groups that are at Risk of Vitamin A Deficiency:

Premature Infants: Premature infants do not have adequate liver stores of vitamin A at birth. Their plasma concentrations of retinol often remain low throughout the first year of life. These infant with vitamin A deficiency have an increased risk of eye, chronic lung, and gastrointestinal diseases.
Infants and Young Children: Unless the mother has Vitamin A deficiency, amounts of vitamin A in breast milk are sufficient to meet infants’ needs for the first 6 months of life. However, prevalence of vitamin A deficiency in developing countries begins to increase in young children just after they stop breastfeeding.
Pregnant and Lactating Women: Pregnant and lactating women need additional amount of Vitamin A for fetal and infant growth and development. These Vitamin A deficiency may result in maternal and infant morbidity and mortality, increased anemia risk, and slower infant growth and development.
People with Cystic Fibrosis: People with cystic fibrosis have pancreatic insufficiency which increases the risk of vitamin A deficiency due to difficulty in absorbing fat.