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

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.

References and For More Information:

https://www.healthandscience.eu/index.php?option=com_content&view=article&id=466:vitamin-a-retinol-and-beta-carotene&catid=54&lang=en&Itemid=327

https://www.sharecare.com/health/vitamin-a/vitamin_a_beta_carotene

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

https://philmaffetone.com/vitamin-a-and-the-beta-carotene-myth/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090096/

https://www.medicalnewstoday.com/articles/252758

https://academic.oup.com/jn/article/133/9/2915/4688113

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/beta-carotene

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jsfa.2647

https://link.springer.com/chapter/10.1007/978-1-4899-1789-8_7

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