Vitamin A: Sources and Benefits

Vitamin A is a fat-soluble vitamin and it includes a variety of related compounds like retinol, retinal and retinoic acid which are also known as retinoids.

There are two types of vitamin A found in the food we eat:

• Vitamin A that is present in animal foods, which is called as preformed vitamin A or Retinol. It is an active form of vitamin A.
• Vitamin A present in fruits and vegetables, which is called as provitamin A or carotenoid, which is converted to retinol in the human body. Beta-carotene is an example of provitamin A which is efficiently converted to retinol by the body.

Functions of Vitamin A in body

Vitamin A is important for many processes in the human body. It is essential for:

• Vision, especially night vision
• Immune functions of the body
• Functioning of the male and female reproductive organs
• Genetic regulation and tissue formation
• Embryonic development
• Development of red blood cells from stem cells
• Maintenance of normal skin and mucous membranes
• Normal iron metabolism

Food sources of vitamin A

Animal sources: meat, eggs, liver, kidney, cod liver oil, fish, shrimp

Dairy sources: whole milk, yoghurt, cheese, butter, paneer

Plant sources: sweet potatoes, carrots, pumpkin, spinach, kale, collard greens, lettuce, bell peppers, broccoli, Tomatoes, grapefruit, cantaloupe, apricots, peach, mango.

Recommended intake of vitamin A

The best way to fulfil the daily requirement of vitamins is to eat a wide variety of vegetables, fruits, fortified dairy products, lentils, legumes and whole grains.

The Recommended Dietary Allowance (RDA) for vitamins indicates the quantity of each vitamin most people should get every day. According to National Institue of Health (NIH), the RDA for vitamin A in:

Children is as follows:

• 0 to 6 months old: 400 mcg/day
• 7 to 12 months old: 500 mcg/day
• 1 to 3 years age: 300 mcg/day
• 4 to 8 years age: 400 mcg/day
• 9 to 13 years age: 600 mcg/day

Teens and adults are as follows:

• Males of age 14 and older: 900 mcg/day
• Females of age 14 and older: 700 mcg/day

(Requirement increases during pregnancy and lactation)

A healthy diet that includes some of the foods listed above (sources) is sufficient for healthy adults to fulfil daily vitamin A requirement. Therefore, healthy adults generally do not require vitamin A supplements.

Causes of vitamin A deficiency

Though vitamin A deficiency is not common in western countries, it is very common in developing countries. It is usually caused by prolonged inadequate intake of vitamin A. It is especially seen in people who eat rice as their main food because rice is a poor source of vitamin A.

Vitamin A deficiency also occurs in people with diseases affecting proper food absorption of nutrients from the intestine. These may include conditions like:

• Crohn's disease
• Cystic fibrosis
• Liver cirrhosis
• Coeliac disease
• Giardiasis
• Disease of pancreas

Some other factors which may cause vitamin A deficiency are:

• Strict vegan diet
• Toddlers and pre-schoolers living in poverty
• Excessive alcohol intake

Symptoms of vitamin A deficiency

Deficiency of vitamin A may cause:

• Dry skin, dry hair and pruritus (itching)
• Broken fingernails
• Infections like chest, throat infections and gastroenteritis
• Delayed growth and development of bones in children
• Miscarriage
• Infertility
• Eye and vision problems which may include:
  • Night blindness (poor vision in the dark)
  • Keratomalacia (Thinning and ulceration of the cornea)
  • Xerophthalmia (Dryness of the conjunctiva and cornea)
  • Bitot's spots (oval or irregular foamy patches on the white part of eyes)
  • Perforation of cornea
  • Damage to retina may cause severe impairment of vision

Investigations

The doctor may advise blood test if he suspects vitamin A deficiency to:

• Rule out any other condition like anaemia
• Confirm vitamin A deficiency

Treatment

• A mild form of vitamin A deficiency may be treated by eating foods rich in vitamin A like chicken, liver, eggs, fortified milk, carrots, mangoes and leafy vegetables.
• For severe forms of deficiency, doctor may advise daily oral vitamin A supplements

Prevention

A regular and consistent intake of foods rich in vitamin A will usually prevent its deficiency. If you are suffering from any long-term illness which prevents your body from absorbing vitamin A from food, get it regularly treated by concerned doctors.

It is recommended to eat at least five servings of fruits and vegetables per day.