Vitamin A

Vitamin A is a fat-soluble vitamin that is stored in the liver.

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

  • Preformed vitamin A is found in animal products such as meat, fish, poultry and dairy foods.
  • Pro-vitamin A is found in plant-based foods such as fruits and vegetables. The most common type of pro-vitamin A is beta-carotene.

IMPORTANCE

  • Vitamin A is also available in dietary supplements. It most often comes in the form of retinyl acetate or retinyl palmitate (preformed vitamin A), beta-carotene (pro-vitamin A) or a combination of preformed and pro-vitamin A.
  • Vitamin A helps form and maintain healthy teeth, skeletal and soft tissue, mucous membranes, and skin. It is also known as retinol because it produces the pigments in the retina of the eye.
  • Vitamin A promotes good vision, especially in low light. It may also be needed for reproduction and breast-feeding.
  • Retinol is an active form of vitamin A. It is found in animal liver, whole milk, and some fortified foods.
  • Carotenoids are dark-colored dyes (pigments) found in plant foods that can turn into a form of vitamin A. There are more than 500 known carotenoids. One such carotenoid is beta-carotene.
  • Beta-carotene is an antioxidant. Antioxidants protect cells from damage caused by substances called free radicals. Free radicals are believed to contribute to certain chronic diseases and play a role in the ageing processes.
  • Food sources of carotenoids such as beta-carotene may reduce the risk for cancer.
  • Beta-carotene supplements do not seem to reduce cancer risk.

SOURCES

Vitamin A comes from animal sources, such as eggs, meat, fortified milk, cheese, cream, liver, kidney, cod, and halibut fish oil. However, all of these sources, except for skim milk that has been fortified with Vitamin A, are high in saturated fat and cholesterol.
The best sources of vitamin A are:
• Cod liver oil
• Eggs
• Fortified breakfast cereals
• Fortified skim milk
• Orange and yellow vegetables and fruits.
• Other sources of beta-carotene such as broccoli, spinach, and most dark green, leafy vegetables.
The more intense the colour of a fruit or vegetable, the higher the beta-carotene content. Vegetable sources of beta-carotene are fat- and cholesterol-free.

DIETARY REQUIREMENT

The amount of vitamin A you need each day depends on your age. Average daily recommended amounts for different ages are listed below in micrograms (mg):
Infants (average intake)
• 0 to 6 months                                                         400 micrograms per day (mcg/day)
• 7 to 12 months                                                         500 mcg/day

Children 
• 1 to 3 years                                                              300 mcg/day
• 4 to 8 years                                                              400 mcg/day
• 9 to 13 years                                                            600 mcg/day
Adolescents and Adults 
• Males age 14 and older                                    900 mcg/day
• Females age 14 and older                              700 mcg/day                                                             (770 during pregnancy and 1,300 mcg during lactation)

INVESTIGATIONS

Blood biochemistry

NORMAL VALUES

Normal values of vitamin A 50 to 200 micrograms per deciliter (mcg/dL) or 1.75 to 6.98 micromoles per litre (micro mol/L).