Vitamin A Deficiency and Toxicity Symptoms

Kale is high in vitamin A and can help prevent vitamin A deficiency.
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The foods you eat every day must provide the nutrients you need to thrive. Vitamin A is one of those essential nutritions. Vitamin A is needed for eye health and good vision, regular cell division and differentiation and it's an important part of normal reproduction.

Vitamin A is a fat-soluble vitamin and it's found in plenty of foods including plants and foods of animal origin. It's not too difficult to get enough vitamin A as long as you have a varied and balanced diet.

There are some key differences between animal and plant sources of vitamin A.

Retinol from Animal Foods

The form of vitamin A found in foods of animal origin is called retinol, or pre-formed vitamin A. Retinol is the most active form of Vitamin A but if you need one of the other forms, called retinal or retinoic acid, your body can take retinol and convert it into one or the other.

You'll find some vitamin A in most animal-sourced foods, but the best sources of retinol are dairy products, eggs, liver and fortified foods.

Vitamin A from Plants

The forms of vitamin A found in plants are called provitamin A carotenoids. The most well-known of the carotenoids are beta-carotene, alpha-carotene, and beta-cryptoxanthin. Your body converts these carotenoids to retinol, but beta-carotene to vitamin A conversion is the most efficient.

Carotenoids also work as antioxidants that may protect your body from free-radical damage, so eating carotenoid-rich foods is important for good overall health.

The best sources of carotenoids are brightly colored and dark green vegetables including carrots, spinach, chard, peppers, squash, and kale, and fruits like apricots, papaya, and mango.

Deficiency Symptoms

Vitamin A deficiency due to poor diet is rare in developed countries and is more likely to result from inflammatory diseases that damage the digestive tract and prevent absorption, such as Crohn's disease and celiac disease.

Alcoholism, zinc deficiency, and pancreatic diseases can also affect the amount of vitamin A in the body.

It's not likely that a typical person will have to deal with a vitamin A deficiency because it's found in so many foods and even a person who eats a less than healthy diet will still probably get plenty of vitamin A. However, a person who doesn't get enough Vitamin A for long periods of time may end up with night-blindness, which is a decreased ability to see in dim light. Another deficiency symptom is diminished immune system function, which means your body will have difficulty fighting infections.

If you have symptoms such as trouble seeing the dark, you should see a health care provider who can order blood tests to determine if a vitamin A deficiency is the problem or if there are other causes.

Can You Get Too Much?

You can get too much vitamin A if you're not careful because since it's a fat-soluble vitamin, your body can store it for a long time in your fat. It's not likely that you'll get too much vitamin A from the foods you eat but taking vitamin A as a supplement can cause problems.

Since vitamin A is found naturally in a lot of foods, supplemental vitamin A is rarely needed and can actually be dangerous.

The tolerable upper limit of vitamin A in adults in 10,000 micrograms. Consuming enormous amounts of vitamin A supplements can result in headaches, dizziness, nausea, vomiting and visual problems.

Hypervitaminosis A is a condition that occurs when your body builds up too much vitamin A over time and can lead to liver problems, weakened bones, and birth defects.

The carotenoids are sold as dietary supplements with the notion they will function as antioxidants, and they are considered to be safer than preformed vitamin A supplements because the body will slow down the conversion from carotenoid to vitamin A as the body stores fill.

However, large doses of carotenoids will give your skin an orange color. Research has shown mixed results on the safety and efficacy of carotenoid supplements, so it's probably best to get your carotenoids from a healthy diet instead of taking dietary supplements.

Sources:

Merck Manual Professional Version. "Vitamin A." 

Office of Dietary Supplements, National Institutes of Health. "Dietary Supplement Fact Sheet: Vitamin A and Carotenoids."

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