187 12.65 Vitamin A Deficiency & Toxicity
Vitamin A deficiency is rare in North America, but is a huge problem in developing countries. In many developing countries, they do not have a stable dietary source of retinoids or provitamin A carotenoids. The figure below gives you an idea of countries where vitamin A deficiency is a problem.
Often the earliest symptom of vitamin A deficiency is night blindness, due to the insufficient production of rhodopsin. The reason that this is the earliest symptom, is that circulating vitamin A levels are homeostatically-controlled, meaning that they do not change until after vitamin A stores are exhausted. This means that blood, serum, plasma measurements are going to appear normal until all stores are exhausted. As a result, sensitively assessing someone as vitamin A deficient can be challenging. There are further changes to the eye that occur during vitamin A deficiency, collectively referred to as xerophthalmia, which are shown in the link below.
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Ultimately the person can become blind. Vitamin A deficiency is the leading cause of blindness in some parts of the world2.
Another symptom of vitamin A deficiency is hyperkeratosis. In this condition, cells overproduce the protein keratin, causing the skin to become rough and irritated, as shown in the link below2.
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One way to counter vitamin A deficiency in developing countries is for staple crops, like rice and corn, to contain beta-carotene. In the case of rice, Golden Rice was genetically modified to produce beta-carotene. A second generation of golden rice, known as Golden Rice 2, has now been developed. However, politics and regulations have prevented it from being used. This is described in the first link. The second link shows some of the opposition to Golden Rice. The third is a nice figure that details the progress towards Golden Rice being used.
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There are also corn varieties that have been bred to produce high amounts of beta-carotene, as described in the link below.
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Vitamin A can be very toxic and can cause serious symptoms, such as blurred vision, liver abnormalities, skin disorders, and joint pain2,3. In addition, research has suggested that people who consume high levels of vitamin A are more prone to bone fractures2. Toxic levels of vitamin A are also teratogenic, which means they could cause birth defects.
This is important to keep in mind because a vitamin A derivative isotretinoin is the active ingredient in the oral acne medication, Accutane. Accutane is effective, as you can see in the video below.
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However, due to the number of adverse events reported from its consumption, Accutane was recalled from the US market in 20094. Isotretinoin medications though are still commonly prescribed.
Retin-A is a topical product of all-trans-retinoic acid. Women of childbearing age need to exercise caution when using these products due to the risk of birth defects, should they become pregnant3. People should not consume huge doses of vitamin A expecting to get the same effects seen from these 2 medications5.
It is important to note that you cannot develop vitamin A toxicity from consuming too much beta-carotene or other provitamin A carotenoids. Instead, a nontoxic condition known as carotenodermia occurs when large amounts of beta-carotene are consumed, where the accumulation of the carotenoid in the fat below the skin causes the skin to look orange, as shown in the link below.
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References & Links
1. http://en.wikipedia.org/wiki/File:Vitamin_A_deficiency.PNG
2. McGuire M, Beerman KA. (2011) Nutritional sciences: From fundamentals to food. Belmont, CA: Wadsworth Cengage Learning.
3. Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill.
4. http://www.drugwatch.com/accutane/
5. Whitney E, Rolfes SR. (2011) Understanding nutrition. Belmont, CA: Wadsworth Cengage Learning.
Links
The eye signs of vitamin A deficiency – http://www.cehjournal.org/article/the-eye-signs-of-vitamin-a-deficiency/
Hyperkeratosis – http://api.ning.com/files/pKcbIy8a8fSwvjlw-NqcoyW-h1U9xsjxM86*Pg7xe7WAS91frtrQFThTH2oDWcMvbUJ9Mlutd3B9tXk8hjbfmXkeZyJs-7Mi/follicularhyperkeratosis1.jpg
Golden Rice – http://www.goldenrice.org/
The Golden Rice – An exercise in how not to do science – http://www.i-sis.org.uk/rice.php
Golden Rice Project – http://www.irri.org/images/golden_rice/GoldenRiceProjectTimelineAugust2013.jpg
New Yellow Corn Could Boost Vitamin A, Save Sight – http://www.npr.org/templates/story/story.php?storyId=18203237
Carotenodermia – http://4.bp.blogspot.com/__7hHVSyD26Y/R8xxsFbRc0I/AAAAAAAAAEs/I73lzYHNE5k/s1600-h/carotenodermia.jpg
Video
Accutane – https://www.youtube.com/watch?v=r93K-w2saPA