This vitamin is unique because it is comprised of more than one molecule. Vitamin A is part of a group known as carotenes. The most popular and most abundant carotene in foods is beta-carotene, which is also known as pro-vitamin A. It’s called that because our bodies convert beta carotene into a form of vitamin A called retinol. After converting beta carotene into retinol our bodies convert it into retinoic acid, the active form of vitamin A that our cells can use.
Beta Carotene (Pro-Vitamin A) —> Retinol —> Retinoic Acid (Vitamin A)
The other carotenes the body can convert into retinol are alpha carotene and beta cryptoxanthin. However, beta carotene is the type of carotene that is most commonly found in foods. Other carotenes that the body can’t convert into retinol include, zeaxanthin, lycopene, lutein. These carotenes are found in foods like Tomatoes, Watermelon and Eggs. These other carotenoids are all very powerful antioxidants that can benefit our bodies greatly.
Vitamin A plays an important role in vision, bone growth, reproduction, cell division, and cell differentiation. One of its primary roles in the body is to help regulate the immune system by making white blood cells and supporting lymphocytes, a type of white blood cell, fight off infections. The vitamin is very essential for fetal growth and development. Too much or too little of the vitamin, especially in fetuses, infants and children, can result in malformations in the skin, eyes, organs, skeleton or nervous system.
As and antioxidant, vitamin A has been sorely understudied and analyzed but it is a very powerful quencher of free radicals in the body. In fact, all the carotenoids found in foods are very powerful antioxidants. In lab studies, lycopene, a carotenoid found in foods like tomatoes and watermelons, was the strongest antioxidant available to us. In these studies, it was 100 times more powerful than vitamin E. However, these were lab studies (i.e petri dish) and not studies done in living cells. Nevertheless, it shows just how powerful carotenoids can be.
Studies note that most of the antioxidants we know about only slow the destructive chain of reaction that free radicals can initiate. Vitamin A however, may stop the chain completely. The vitamin is thought to work as a team with vitamins C and E to neutralize free radicals. Unfortunately, very few studies have been done to examine this antioxidant pathway.
Recommended Dietary Allowances (RDA) for Vitamin A
|400 mcg||400 mcg|
|7–12 months||500 mcg||500 mcg|
|1–3 years||300 mcg||300 mcg|
|4–8 years||400 mcg||400 mcg|
|9–13 years||600 mcg||600 mcg|
|14–18 years||900 mcg||700 mcg||750 mcg||1,200 mcg|
|19–50 years||900 mcg||700 mcg||770 mcg||1,300 mcg|
|51+ years||900 mcg||700 mcg|
mcg = micrograms
IU = International Units
- 1 IU retinol = 0.3 mcg
- 1 IU beta-carotene from dietary supplements = 0.15 mcg
- 1 IU beta-carotene from food = 0.05 mcg
- 1 IU alpha-carotene or beta-cryptoxanthin = 0.025 mcg
If you elect to or must use supplements in order to get enough vitamin A into our daily diet. Get Mixed Carotenoids (1.5 – 2 mg or 3500 IU’s) and not retinol. The retinol used in supplements tends to be synthetic and may be toxic in higher doses. In addition, you should not get vitamin A supplements as retinol because it may interfere with the functioning of vitamin D in your body. Your best bet is to get mixed carotenoids. These include alpha and beta carotene, lutein and lycopene along with other carotenoids. Some sources suggest doses as high as 10,000 – 20,000 IU’s of mixed carotenoids daily. Check with your doctor or health professional to see if these doses are right for you. Beta carotene is sold alone as a supplement but make sure its from a natural source and not synthetic. You best bet, however, is to eat a healthy diet where you get 100% of your RDA of vitamin A.
- The Dr. Oz Show
- Ganji V, Hampl J, Betts N. Race-, gender- and age-specific differences in dietary micronutrient intakes of US children. International Journal Of Food Sciences And Nutrition. 2003;54(6):485-490
- European Responsible Nutrition Alliance (ERNA), 2004 Vitamin-A fact sheet. Located at http://www.erna.org/UserFiles/Vitamin%20A.pdf.
- Weil, Andrew. Natural health, natural medicine: a comprehensive manual for wellness and self-care. 2004.