Vitamin A is a fat-soluble vitamin. It is commonly available through various dietary supplements and stored in the liver. The main forms of Vitamin A that are present in foods includes 3 categories:
- Preformed vitamin A in the form of retinyl acetate or retinyl palmitate. It is found in animal based products
- Provitamin A which includes beta-carotene. It is found in plant-based foods
- Combination of preformed and provitamin A.
Vitamin A is involved in different functions of the body. This includes embryonic development and reproduction, regulates bone metabolism, and maintains the health of skin, teeth and mucous membrane. Here are its key functions:
- Regulates vision: Vitamin A is required by the retina to form rhodopsin. Rhodopsin is the light-absorbing molecule that plays an important role in controlling our low-light vision and color vision.
- Acts as an Antioxidant: Beta-carotene, protects from the cell damage caused due to the release of free radicals. Free radicals are involved in certain long-term diseases and aging.
- Maintain skin’s health: Vitamin A helps in the differentiation of immature skin cells into mature epidermal cells.
- Develops Immunity: Vitamin A regulates T cell differentiation and proliferation.
- Gene transcription: The retinoic acid form of Vitamin A is necessary for gene transcription
- Regulates fetal growth and development
- Keeps the mucous lining of nose and mouth strong and healthy
Excellent sources of vitamin A includes turkey giblets and beef liver. Plant based foods that are rich in vitamin A includes kale, sweet potato, pumpkin, spinach, papaya, cantaloupe, and apricot.
Recommended dosage (RDA)
The Recommended Dietary Allowance for adults men is 900 mcg (equivalent to 3,000 IU) and 700 mcg RAE for women (equivalent to 2,333 IU).
Lack of sufficient intake of Vitamin A leads to Vitamin A deficiency. It can be of two types, primary and secondary deficiency.
Primary vitamin A deficiency
Primary vitamin A deficiency is mainly seen among children and adults. Individuals who do not consume appropriate amount of vitamin A through diet are prone to this type of deficiency. Babies who are subjected to an early weaning from breast milk have a high risk of getting vitamin A deficiency.
Secondary vitamin A deficiency
Secondary vitamin A deficiency can occur due to several reasons such as impaired bile production, chronic malabsorption of lipids and intake of low-fat diets.
Being a fat-soluble vitamin, it depends on micellar solubilization for dispersion into the small intestine. Therefore, a low fat diet will result in poor intake of vitamin A and impair its absorption. Another important factor that is involved in the transportation and metabolism of vitamin A is Zinc, hence Zinc deficiency will impair synthesis of vitamin A.
Signs and symptoms
The initial manifestations of vitamin A deficiency is impaired vision and night– blindness (Mainly in reduced light).
Vision is compromised resulting in total blindness and in severe cases results in xerophthalmia and other complications such as:
- Dryness of the conjunctiva (xerosis)
- Accumulation of keratin debris (Bitot’s spots)
- Damage to the corneal surface (keratomalacia)
Other complications seen are,
- Weakened teeth (Enamel hypoplasia).
- Higher risk of ear infections and urinary tract infections
- Meningococcal disease
Vitamin A is one of the most important fat soluble vitamin. It plays a structural role in building the immunity and in overall development and growth of human body. You should always have foods that have sufficient levels of vitamin A, whether it is animal or plant based.