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Vitamin A: Fat-Soluble Vitamin Deficiency and Toxicity Symptoms

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  • 0:01 Vitamin A
  • 1:51 Night Blindness
  • 3:08 Xerophthalmia
  • 4:12 Toxicity
  • 5:47 Lesson Summary
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Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Vitamin A is a fat-soluble vitamin that is important for vision and cell differentiation. Learn about conditions that can result when vitamin A is deficient, including night blindness and xerophthalmia, as well as symptoms of toxicity, in this lesson.

Vitamin A

Did you ever sneak out of a movie theater to grab a bowl of popcorn only to return to the theater feeling like you were blinded by the darkness? If so, you likely noticed that your eyes adjusted to the dark within a few minutes. This adjustment is thanks to rhodopsin, which is a light-sensitive pigment in the retina of your eyes that helps you see in dim light.

Vitamin A is an essential component of rhodopsin. Oh, and by the way, carrots are a good source of vitamin A - this explains why your mom used to tell you to eat your carrots so you could see better at night! In this lesson, you will learn more about what vitamin A does for you and what happens if you get too little or too much of this nutrient.

Let's start by building our understanding of vitamin A. You get this vitamin from the foods you eat, and different foods contain different forms of vitamin A. One form is referred to as retinol, or preformed vitamin A. It's the most useful form of vitamin A because it's easily absorbed by your body. This is likely because retinol is found in animal-based foods like liver, fish, eggs and dairy products. Because animals have this form of vitamin A inside of them, when you eat the animal product, it's already in the ideal form to be handled by you. In other words, it's pre-formed and ready to go.

The other form of vitamin A is beta-carotene, which is a provitamin A. This form must be converted to vitamin A inside your body. Beta-carotene is found in plant-based foods like fruits and vegetables, especially those that have yellow-orange pigments, like carrots. It's almost like a provitamin is the beginning of a vitamin, like the prologue is the beginning of a novel.

Night Blindness

As you see, vitamin A can be found in a variety of foods, but vitamin A deficiency can occur if you are not eating enough of the foods that contain this vitamin. For example, most of us don't eat enough fruits and vegetables, but love to eat bread and other grains, which provide little, if any, vitamin A. We also see that both forms of vitamin A rely on fats in the diet for proper absorption, so if you follow a strict low-fat diet, you could put yourself at risk of a deficiency.

We already mentioned that vitamin A is needed for vision in dimly lit rooms thanks to its role in the making of rhodopsin. So, what happens if you have a vitamin A deficiency? Well, the answer is you will suffer from night blindness, which is abnormally poor vision in dim light.

If we look back at our example, when you went into the well-lit lobby of the movie theater to get your popcorn, the bright lights caused the decomposition of the stored rhodopsin in your eyes. When you went back in the dark theater it took a few minutes for your body to make more rhodopsin, hence the adjustment period. If there's not enough vitamin A to make new rhodopsin, your eyes will have a hard time adjusting, giving you night blindness.

Xerophthalmia

Another function of this vitamin is that vitamin A helps with cell differentiation, which means that vitamin A helps immature cells become specialized cells. It's kind of as if the immature cells are a bowl of plain vanilla ice and vitamin A is the secret ingredient that can turn them into the different types of sundaes.

This role of vitamin A is particularly important for the cells of your eyes. The lining of your eye contains cells that secrete mucus that is needed to keep your eyes moist. When these cells die, immature cells must be differentiated to become new mucus-secreting cells. If vitamin A is deficient, this does not happen, leading to xerophthalmia, which is an abnormal dryness of the eyes. To recall this term you might want to think of the prefix 'xero-' as the value zero, meaning there are 'zero tears' to wet your eyes, and that leads to 'optical' problems, maybe even a visit to your 'optometrist.'

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