VITAMIN A – RETINAL

 

SQUASH

IMPORTANT: The information on this site should never be used to self medicate or to self diagnose.  Always contact your health care provider before using any kind of supplementation or making any extreme change in diet. 


VITAMIN A

morguefile8531273691423The smell of freshly steamed carrots with a dollop of dilled butter on top wafted upwards from my plate as we sat enjoying the rays of the evening sun.  The light filtered down through the tree branches catching the glistening surface of the small, tender carrots as the melting butter slid over their sides gently coating them.

“Carrots. What’s in a carrot anyway,” I mused?

My friend Rooter is a research reporter with a passion for food and anything related to it.  He specialises in gleaning information from research papers on nutrition and how food affects our bodies.  Unable to withhold the information on the tip of his tongue he began:

“There are many good things in carrots but the most notable would be vitamin A, “ he said,  ” that wonderfully powerful little vitamin that does so much to give us a good life”.

“It helps us to see;  empowers our immune system;  helps embryos grow in the womb;  works with calcium, vitamin D and vitamin K to create healthy bones;  gives us healthy skin;  works with stem cells to produce red blood cells;  copies our genes DNA to RNA  and if all that is not enough it also acts as an antioxidant to protect our cells from damage.“

Caught up in his enthusiasm I asked  “We can get all this from eating Carrots?”

“Yes, so let’s eat.”

” Eat. OK Great!  I’m hungry.”

“Can we get vitamin A from other sources?” I asked.

“Absolutely,”  he said.   “Vitamin A comes from plants and from animals. The most abundant source comes from beef and particularly beef liver.”

“Yech,” I said, “ liver is one food I can do without.”

“Well, you don’t have to get it from liver.  Four ounces of roast beef will give you 4 to 5 days supply of vitamin A.  I’ll tell you something that you might not know.  There is a  difference between vitamin A from animals and vitamin A from plants?”

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“Really?”

“You bet, but few people know this.”

He went on to explain the differences but instead of repeating it word by word I’ll give you the gist of what was said.

 

WHAT IS VITAMIN A?

Animal sources of Vitamin A give us the actual vitamin in the form of a compound called retinal.  From retinal (or retinol)  retinoic acid can be produced.  Retinal is housed in a chemical compound called an ester and is stored in the liver.

The storage of vitamin A in the liver is how the body builds supplies of vitamin A that can last for a very long time.

Plant sources on the other hand give us a compound called a carotenoid.  There are two types of carotenoids:

1. Caroteins: ex: alpha carotene, beta carotene, gamma carotene & lycopene.  Caroteins have non-oxygen containing molecules

Diets rich in carotenoids lead to better health and lower death rates from many chronic illnesses.

2. Xanthophylls: ex:   beta-cryptozanthin, lutein & zeaxanthin.  Xanyhopylls have oxygen containing molecules.

There are only four carotenoids that can be converted by enzymes to Vitamin A or retinal.   The four are beta carotene, the most prevalent, then alpha carotene, then gamma carotene & finally beta cryptozanthin.

The only way they can be successfully converted is with ‘fat’  because they are fat soluble.   So….…you know those fat free dressings and fat free this and fat free that….…well free yourself of them if you want to get some vitamin A into your body by eating your vegetables.   Vitamin A is a fat lover.

I’m not saying we should eat gross amounts of fat but a little healthy fat such as olive oil or organic canola oil on our salad is a good thing, even some of that butter.

Only about 1/12 of the carotenoids called beta carotene can be transformed into Vitamin A and that is when it is eaten with some fat. The other carotenoids produce even less.

In a really healthy diet the liver stores enough Vitamin A to last almost a year.   That is, if you had a full supply of vitamin A stores in your liver and you decided to eat nothing that has or makes vitamin A in the body you would probably be good for almost a year.

 

THE JOURNEY

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WHAT DOES VITAMIN A DO FOR US?

When required by a particular part of the body, the liver releases some vitamin A from its packages and transports it in the blood attached to a protein carrier which delivers it to the target cells.

The target cells include those for:

 

Vision

openclipart.orgEYES

The protein transporters deliver the vitamin A in its retinal form to the eyes where it is used to help our eyes to see through a long chain of biological events.  A very important role of a form of retinal is used to reform rhodopsin in the retina.  Rhodopsin is needed to see black and white (so you can read this) and it helps us see at night.


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In the form of retinoic acid vitamin A plays an important role in ‘gene transcription’.  This is the process where the messenger RNA copies the information from the template of DNA and provides the instructions to the cell.

 

 

The Skin

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In the form of retinoic acid, vitamin A appears to function by maintaining normal skin health.  The research on this is ongoing and an understanding of the role it plays remains unknown.

 

 

Immunity

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Vitamin A is required for normal functioning of the immune system and is often referred to as the anti-infective vitamin.  In the form of retinol it helps maintain the integrity and function of the cells in the lining of the airways and digestive tract which form the first line of defence against infection.  In the form of retinoic acid it is central to the development of lymphocytes a type of white blood cell which plays a critical role in immune response.

 

 

 

Growth and Development

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Both forms of vitamin A, retinol and retinoic acid, are essential for embryos to develop helping to form the heart, eyes and ears and to regulate how genes act in producing growth hormones.

and finally….…

 

 

 

 


Red Blood Cell Production

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Vitamin A helps with the production of red blood cells from hematopoietic stem cells which are dependent on retinoids  and it  helps with the transfer of iron from storage areas in the liver for the development of  red blood cells for use by hemoglobin ( the oxygen carrier in red blood cells). 

 

WHAT HAPPENS WHEN WE DON’T GET ENOUGH VITAMIN A?

All of these systems suffer.  We have trouble reading.  Our DNA is compromised.  Our skin is not properly protected. Our growth as children is stunted and our red blood cell production is adversely affected.

 

WHAT HAPPENS WHEN WE GET TOO MUCH VITAMIN A?

When required by a particular part of the body, the liver releases some vitamin A from its packages and transports it in the blood attached to a protein carrier which delivers it to the target cells.

Now, just for fun let’s say that those carrots smothered with dilled butter have been eaten.  Let’s follow what happens with the vitamin A production, storage and use in our bodies.

The carrots and butter after getting digested in the stomach enter the small intestines where they are further transformed.

First the butter.  Butter, which contains retinal, is from an animal and remember animal sources of retinal/retinol are already vitamin A.  Vitamin A is just a generic name for the chemical one.  It is here in the small intestines that the retinal in its ester form is transported to the liver by fat particles called chylomicrons.  In the liver it is stored as retinal in esters.  Over 90% of retinal is stored in the liver in special cells called hepatic stellate cells along with lipids (fats).

It is possible to get too much Vitamin A from animal sources.

Because vitamin A from animal sources is ready made it goes directly into the liver to be stored.

When retinol levels rise so do the size of the hepatic stellate cells.   Once these cells are full to the brim the excess vitamin A in them is redirected to the bloodstream causing systemic toxicity.  In other words it becomes a poison.

If this happens  a whole lot starts to go wrong with us such as nausea, jaundice, anorexia (not nervosa), vomiting, blurry vision, hair loss altered mental status.   You get the picture.  It’s not a good thing.   This only happens when too much vitamin A is consumed from food from animals. If for instance you ate liver in large quantities over an extended period of time.

Next, the carrots with beta carotene:  this source of vitamin A is processed differently.   It, too, is processed in the small intestine.  It is partially converted to vitamin A by the enzyme ‘dioxygenase’.  This conversion is dependent on a mechanism in the body which regulates the amount of vitamin A the body needs called the vitamin A status. The vitamin A status only allows as much beta carotene to be converted as is needed to maintain the accepted level.  This vitamin A is delivered to the liver to be stored for use.  The rest of the beta carotene which was not converted is stored in fat cells throughout the body where it can be converted as needed.

Because of this regulatory system it is not possible to get an overdose of vitamin A from plant sources.  It has been found, however, that excessive amounts of beta carotene taken in supplement form is not beneficial and may actually cause harm.

An interesting discovery was made when researchers found that if we are eating a well balanced diet when we are younger our bodies build up large stores of vitamin A.  Keeping these stores topped-up throughout our lives is not difficult if we continue to eat a well balanced diet.

As for those unfortunate souls who spend their lives eating hamburgers, french fries and drinking soft drinks, well…… its just too sad.  No wonder they start suffering from all sorts of diseases.

 

WHERE DO WE GET VITAMIN A? 

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You can also get the recommended levels of vitamin A from the following beta carotene containing plant sources:  apricots, asparagus, broccoli, brussels sprouts,  celery, chili peppers, green peas, leeks, mustard greens, oranges, plums, squash, swiss chard, tomatoes, turnip greens

Some other foods which have vitamin A in its retinol form are: liver, beef, butter, cod liver oil, eggs, cheese and milk.

 

FACTOIDS:

The recommended daily allowance for vitamin A is 870 RAE’s or 4500 IU’s (international units) per day.

A piece of beef the size of your fist has almost 4000 RAE’s.

Most other meats such as lamb, pork and chicken do not contain high levels of vitamin A nor does fish.

 

REFERENCES:

Linus Pauling: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA

Wikipedia:  http://en.wikipedia.org/wiki/Vitamin_A

Health Canada  http://www.hc-sc.gc.ca/fn-an/index-eng.php

USDA Nutritional Values  http://ndb.nal.usda.gov/

The World Health Organization  http://www.who.int/topics/en/