As a child when you were told to eat your carrots so you could see in the dark, vitamin A was the nutrient that would allow you to do so. Vitamin A is a group of organic compounds which include retinol, retinal, retinoic acid, and carotenoids.
The Properties Of Vitamin A
Vitamin A is a fat soluble vitamin that is very vital for maintaining normal vision, bolstering our immune system as well as a series of essential metabolic processes.
There are two basic types of vitamin A: performed, also known as retinol and provitamin A, of which the most common is beta-carotene. Retinol is found in meat (especially the liver), fish and dairy products. Provitamin A is found in many fruits and vegetables that we eat along with other plant-based products. Generally, you will find vitamin A in the bright yellow and orange vegetables like carrots, yellow squashes and sweet potatoes, dark leafy green vegetables like kale and many dried herbs and orange and red seasonings such as paprika, cayenne pepper, chilli pepper and red peppers.
The Function of Vitamin A In Our Bodies
Vitamin A is necessary for many different organs to function properly in our bodies. Both performed vitamin A and pro-vitamin A need to be metabolized in our bodies to retinal and retinoic acid to be used by the various cells and organs. Some the vital functions of vitamin A are:
- Eyes: Critical for our vision, vitamin A is a necessary component of rhodopsin, which is a vital protein that helps the receptors in the retina absorb light. It is also helps support the normal function and separation of the conjunctiva, a thin membrane that covers the inside of the eyelids and the white part (sclera) of the eye, and the cornea.
- Heart, Lungs and Kidneys: Vitamin A is essential for the normal formation and function of these vital organs. It is vital for the normal cell formation and communication.
- Immune System: Vitamin A is a powerful anti-oxidant¹. Anti-oxidants play an important part in protecting and repairing our cells from damage that is caused by free-radicals. Free radicals are formed when molecules are excited or bonds are cleaved, resulting in a species with a spare valence electron in it’s outer shell. These species are highly reactive and constantly search for something to pair up with. This is where the damage to our cells comes in and the damage to our immune system. Free radicals have been associated with some chronic diseases such as cancers and arthritis. Anti-oxidants such as vitamin A help to keep the immune system functioning properly so that we can fight off viruses, bacteria and the damages caused by the free radicals.
- Cellular Communication: Although the exact mechanism is not understood², it is believed that vitamin A and specifically beta-carotene is used to help cells communicate through the gap junction. Since many cancers inhibit this communication through the gap junction, beta-carotene is also useful in protecting against cancer.
What Happens When We Don’t Have Enough Vitamin A
Vitamin A deficiency is relatively rare in the United States, but is commonly seen in third world or developing countries. The people most affected are young children and pregnant women. The most common symptom of vitamin A deficiency is the inability to see in low light. Persistent deficiency can lead to blindness.
Can I Have Too Much Vitamin A
Short answer is yes. Because vitamin A is a fat soluble vitamin, our bodies store it up in the liver. While having too much of the pro-vitamin A, the beta carotenes and those found in plants, does not show any problems, preformed vitamin A can be harmful, leading to dizziness, increased intracranial (head/brain) pressure, headaches, nausea, pain in the joints and bones, skin irritations, coma and death.³
The Recommended Vitamin A Intake By Age
The maximum amount of vitamin A that our bodies need differs with our age. Here are the daily recommended allowances (RDA) according to the U.S. Institute of Medicine of the National Academy of Sciences:
- Age 18 and Older: Men: 900mcg/3,000 units
- Women: 700mcg/2,300 units
- Pregnant Women Over Age 19: 770mcg/2,600 units
- Lactating Women Over 19: 1,300 mcg/4,300 units
- Children 1-3 Years Old: 300mcg/1,000 units
- Children 4-8 Years Old: 400 mcg/1,300 units
- Children 9-13 Years Old: 600mcg/2,000 units
- Children 14-18 Years Old: 750mcg/2,500 units
Eating 5 servings a day of fruits and vegetables will supply about 50-65% of the RDA of vitamin A. Most multivitamins contain vitamin A, and eating dairy and fish products will also increase your vitamin A.
When it comes to vitamins and minerals, vitamin A is essential. It helps maintain healthy vision, is a powerful anti-oxidant that helps repair and protect our bodies and cells from damage and chronic disease, supports our immune system and helps our organs develop and function properly. By using this guide to vitamin A, you will be able to have enough in your diet as well as understand its function.
¹ Albanes D, Heinonen OP, Taylor PR, et al. Alpha-Tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance. J Natl Cancer Inst. 1996; 88:1560-70.
² Vitamin D influences gap junctional communication in C3H/10T View the MathML source murine fibroblast cells. FEBS Letters. Volume 352, Issue 1, 19 September 1994, Pages 1–3.
³ Dietary Reference Intakes for Calcium and Vitamin D.