Vitamin A is one of our fat soluble vitamins, meaning that it is stored in adipose tissue, as well as in the liver and skeletal muscle. Vitamin A is required for normal vision and it is found in two forms in our diets. The most bioavailable form is called retinol (or retinoids) and is found in animal foods (like eggs and liver). The other form is called pro-Vitamin A (also known as carotenoids) is found in plants foods and must be converted into the active form (however many people are not able to convert carotenoids to retinol).
Benefits of Vitamin A
- Cellular growth and tissue healing – this vitamin is involved in laying down new bone during growth and promoting healthy teeth
- Immune system function – it stimulates the production of mucous thereby protecting tissues during an infection and promoting rapid recovery
- Healthy vision – Vitamin A is needed to prevent night blindness; Vitamin A is involved in the formation of rhodopsin which allows us to see at night
- Antioxidant – protects the cell membranes and tissue lining from free radical damage
- Nourishes the skin – it helps the skin progress from less to more mature cell forms
- Promotes healthy reproduction – Vitamin A deficiency has been linked to male factor infertility and poor egg quality in females. This vitamin is also necessary to ensure normal growth and development of embryos.
Factors that impede conversion of carotenoids to the bioavailable form of Vitamin A (ie retinol)
- Alcohol consumption
- Digestive diseases such as IBD (Crohn’s and colitis), liver and gallbladder diseases
- Cystic fibrosis
- Some medications (ie cortisone)
- Low fat diets
Symptoms of Vitamin A deficiency
- Decreased immune function
- Vision impairment/night blindness
- Mood disorders
- Thyroid imbalance
- Skin issues – dry skin/acne/eczema
Food sources of Vitamin A
- Retinoids sources – animal liver, fish liver oil, egg yolks and milk products
- Carotenoid sources – yellow and orange colored fruit and vegetables such as carrots, squash, yams, pumpkin, sweet potatoes, apricots, mangoes, peaches, cantaloupe and papaya as well as green leafy vegetables like kale, broccoli, spinach, asparagus and lettuce
Vitamin A and Toxicity
Since Vitamin A is a fat soluble vitamin, it is stored in the body for a longer period of time and therefore can be more toxic than water soluble vitamins. Symptoms of Vitamin A toxicity include hair loss, liver damage, confusion and bone loss.
Recommended Dietary Allowance
The RDA of Vitamin A for adults is 2,000-3,000 IU; for pregnant females it’s 3,000 IU but 10,000 IU is safe and generally the recommended amount to consume daily. About 10,000-15,000 IU of beta carotene will convert into Vitamin A.
Vitamin A supplementation and pregnancy
Although Vitamin A is required during pregnancy, excessive amounts can be harmful to a developing fetus, so it is not recommended to take extra retinol while pregnant. Congenital birth defects such as malformations of the eyes, skull, lungs and heart have been linked to high doses of retinol while pregnant. Beta-carotene has no known teratogenic effects, even if large doses are consumed. However, it is recommended to get Vitamin A through diet as much as possible.
Vitamin A Solomons NW. Vitamin A. In: Bowman B, Russell R, eds. Present Knowledge in Nutrition. 9thed. Washington, DC: International Life Sciences Institute; 2006: 157-83.
Vitamin A in Reproduction and Development. Margaret Clagett-Dame and Danielle Knutson. Nutrients 2011 Apr; 3(4): 385–428.