Despite the concern about the potential of vitamin A toxicity among people who use excessive amounts of supplements, it is possible to be deficient of vitamin A. This is mainly seen in the elderly, chronically ill and people who are malnourished. It is uncommon in the United States but is being seen more frequently among vegans, alcoholics, people who undergo small bowel bypass surgery and immigrants from developing countries¹.
What is vitamin A deficiency?
Vitamin A deficiency is a lack of sufficient vitamin A in the body to maintain health and prevent deficiency-related conditions like night blindness. Deficiencies also impair immune defenses and can affect the formation of blood cells. It also affects skin, hair and nail health. Vitamin A is a fat-soluble vitamin and can be stored in the body for long periods of time. Supplementation of these vitamins are therefore usually not necessary².
Due to the possibility of toxicity, supplementation should be avoided in people who do not have a deficiency. A balanced diet will suffice for the daily vitamin A requirements. In fact vitamin A intake is not required daily due to the body’s ability to store vitamin A. The maximum daily dose is only exceeded when a vitamin A deficiency has been confirmed by a medical doctor.
Sources of Vitamin A
Vitamin A is acquired from the diet and cannot be manufactured by the human body. There are 3 forms of this vitamin – retinols, beta carotenes and carotenoids.
- Of these three forms, retinols are the most active form. It is also known as preformed vitamin A. The main source of retinols is found in animal foods, like meat.
- Beta carotenes are known as provitamin A and found in plant sources. It is considered as the plant source of retinols.
- Carotenoids are pigments found in certain plants, algae and bacteria that can produce nutrients from light (photosynthesis). There are about 600 types and is divided into carotenes and xanthophylls.
A balanced diet with a combination of animal and plant based foods is usually sufficient to prevent a vitamin A deficiency.
Causes of Vitamin A Deficiency
A vitamin A deficiency can be divided into primary and secondary causes. In developing nations, the primary causes is more common while in developed nations a vitamin A deficiency is more commonly due to the secondary causes discussed below.
Primary vitamin A deficiency is a result inadequate vitamin A intake. This means not eating enough foods with vitamin A, as is seen in certain endemic areas where the staple diet lacks foods rich in vitamin A. It can also occur with extreme dieting, prolonged fasting and severe malnourishment due to starvation.
Secondary vitamin A deficiency occurs when the body is unable to absorb vitamin A from food or there is some underlying disease where the transport and storage of vitamin A is impaired. This is seen with:
- Bile duct stones or strictures
- Celiac disease
- Cystic fibrosis
- Duodenal bypass
- Exocrine pancreatic insufficiency
- Inflammatory bowel disease (IBD)
- Liver diseases like cirrhosis
- Prolonged gastroenteritis like with giardiasis
Signs and Symptoms of Deficiency
The signs and symptoms of vitamin A deficiency depends on the degree and duration of the deficiency. It can also present slight differently in children and adults. The signs and symptoms includes:
- Difficulty seeing in low light environment.
- Dryness and thickening of the conjunctiva and cornea.
- Corneal ulcers which may lead to hazy vision.
- Drying, scaling and thickening of the skin.
- Keratinization of the gastrointestinal, respiratory and urinary tracts.
- Frequent infections due to a weakened immune system.
- Growth retardation in children (severe and prolonged deficiencies).
- Fatigue often associated with anemia.
- Dry hair and brittle nails.
- Itchy skin (pruritus).
Foods Rich in Vitamin A
As has been previously stated, vitamin A intake does not have to be daily since the body can store this vitamin. About 80% to 90% of vitamin A is stored in the liver. This is one of the reasons why animal liver is considered to be a good source of vitamin A. The retinols which are the more active form of vitamin A are derived mainly from animal-based foods while beta-carotene which can be converted into vitamin A is mainly found in plant-based foods.
Therefore the foods that are rich in vitamin A include:
- Animal liver, including meat and poultry.
- Oily fish and other seafoods such as oysters and eels.
- Cod liver oil.
- Milk and dairy products such as cheese.
- Dark leafy green vegetables like spinach.
- Orange vegetables like carrots and pumpkin.
- Fruits like apricots and cantaloupes.
Recommended and Maximum Doses
Doses in infants and children should be discussed with a dietitian and pediatrician. It varies by age. For adults, the doses for vitamin A includes:
- Men (19 years and older) = 900 mcg/day
- Women (19 years and older) = 700 mcg/day
- Pregnant women = 770 mcg/day
- Breastfeeding women = 1,300 mcg/day
The maximum daily dose that should not be exceeded is 3,000 mcg/day. These doses are required in order to provide sufficient vitamin A for the body’s needs and to prevent a deficiency. Higher doses usually in the form of supplements are only needed in a deficiency and using these supplements unnecessarily can lead to toxicity.
Read more on vitamin A toxicity.
Vitamin A Supplementation
The focus should always be on prevention of vitamin A deficiency with the consumption of balanced meals. However, when deficiency syndromes do arise then supplementation becomes necessary. Multivitamin supplements containing vitamin A usually has it in low doses. When vitamin A deficiency is present then supplements may be prescribed to ensure the following doses to prevent the deficiency:
0-3 years = 600 mcg (2000 IU)
4-8 years = 900 mcg (3000 IU)
9-13 years = 1700 mcg (5665 IU)
14-18 years = 2800 mcg (9335 IU)
All ages = 3000 mcg (10,000 IU)
The appropriate dose should be prescribed by a doctor. It is important to note that vitamin A toxicity is more likely to arise with the use of supplements. Therefore supplements should not be routinely used by people who do not have a vitamin A deficiency and eat an otherwise healthy diet. Always consult with a doctor in order to undergo the relevant tests and confirm vitamin A deficiency prior to commencing with a supplement.