What is vitamin A?
Vitamin A is a fat-soluble vitamin (click here learn more about the difference between fat and water soluble vitamins). Vitamin A comes in two forms--preformed and compound. The preformed vitamin A is an active form found in animal products while the compounded form is found in plant sources. The compounded (plant source) form of vitamin A is activated in the human body when it is metabolized.
You may have heard of some of the forms listed below, such as 𝛃-carotene (beta-carotene). It is important to be aware of these other forms so that you can differentiate them in supplemental products. If you have any questions or doubts, reach out to your healthcare team or dietitian to ask about your concerns.
What does the body use Vitamin A for?
Vitamin A functions as an antioxidant, which means it helps to prevent or slow damage to cells. One of the more well-known functions of vitamin A is to support night vision and play a role in visual pigmentation. It can also be protective to our eyes, especially in the case that they are strained looking at a computer or other screens throughout the day.
This vitamin is necessary for normal growth and development processes and plays a crucial role in cell differentiation and regulating genes. Vitamin A plays a role in growth hormone synthesis as well as reproduction. It also helps to maintain the thin linings of organs and blood vessels in the body. It aids in the development of teeth and bones as well. When it comes to skin, it also has an important role. Vitamin A is necessary for cell turnover, renewal, and repair, and it helps to defend the skin against ultraviolet (UV) radiation.
Recommended Dietary Allowance
Primary deficiency results from inadequate intake.
Secondary deficiency happens due to mal-absorption. This can be caused by any one (or a combination of) the following:
Insufficiency dietary fat
Biliary or pancreatic insufficiency
Impaired transport in the body
Protein-energy malnutrition (PEM)
Map of Vitamin A deficiency (VAD) . Deficiency is rare in the United States (generally associated with mal-absorption) but is more common in developing countries. VAD is one of the most significant causes of blindness in the developing world.
Symptoms of deficiency
Impaired vision (loss of visual pigmentation), manifesting as night blindness (nyctalopia)
Inability to see in dim light or twilight
Impaired embryonic development
Declining bone health
Changes in skin texture (dry, scaly, rough)
Damage to body’s vessel, tissue, and eye linings
Blindness and eye damage
Increased susceptibility to infections
Vitamin A is toxic in large amounts. Usually, misuse of supplements is the cause of chronically high intakes. This is due to the fact that it begins to exceed the amount that the liver can store healthily. Essentially, too much Vitamin A can intoxicate the body and lead to liver disease.
Upper Limit (UL): also known as the Tolerable upper intake level; largest daily intake of a nutrient that is considered safe for most people; exceeding this limit is not recommended and may cause harm to the body; Set by the Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine.
Symptoms of Toxicity
Acute toxicity is when the level of vitamin A suddenly increases over a short period of time.
Chronic toxicity is when the level of vitamin A is in excess over a longer period of time.
Dry skin and lips
Patchy, red skin (erythema) that is scaly or peels
Headache and/or mental disturbances
Nausea and vomiting
How to test your levels of Vitamin A
These tests should be run under direct medical supervision. Ask your doctor and dietitian for more information.
Plasma retinol concentration levels (blood levels)
Dark adaptation testing (IOM, Food and Nutrition Board, 2001)
Pupillary Response test
Blood calcium test
Liver function test
How stable is Vitamin A?
Vitamin A is stable in light, heat, and in usual cooking processes. It can be destroyed by drying, very high temperature, and ultraviolet (UV) light.
Supplementation & Treatment with Vitamin A
Vitamin A deficiencies are usually treated with oral doses if an acute (temporary) situation. In a more chronic situation such as one associated with malnutrition, the malnutrition (root cause) must be treated first in order to benefit from the treatment of vitamin A by supplementation.
Treatment for vitamin A toxicity usually involves stopping supplementation of vitamin A for a defined period of time. In rare cases, it may also be recommended to stop eating foods high in vitamin A. Again, this should be closely monitored by your treating physician and dietitian and not something you conduct on your own.
FREE Patient Resources
Resource for Professionals & Providers
Don't you wish you had a quick reference to brush up on vitamin A before seeing your clients or patients? This quick reference will help you organize your thoughts and prove to be a great resource in between appointments. Upon purchase, a high quality pdf file will be available for download. From there, you can turn the file into a print-out, poster, or whatever you would like!
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