Sitting around the table over the Fourth holiday with inquisitive grandkids, someone asked the question “What is vitamin A and what does it do?”

Trying to explain complex biological processes to sponge-like minds with brief attention spans is a challenge. I used to bore my own kids, and many patients, with long, detailed orations that didn’t hold their audience very well. I’ll try here anyway. And I can’t hear you snore.

Vitamin A is the name of a group of chemically related fat-soluble organic (which means they have carbon atoms in them) compounds usually called retinoids (RET-in-oyds) after retinol, the main type found in animal flesh. The name derives from the retina in eyes, where retinol becomes a form called retinal, which binds to a retina protein opsin to form rhodopsin, a light-absorbing molecule. This is important for vision, especially night vision.

For our purposes we’ll call all retinoid variations vitamin A. It is present in many foods.

We can’t make it, so we must eat it to absorb it. The two main kinds are preformed vitamin A as retinol, its main storage form in liver. Retinol comes mostly with consuming fish, poultry and dairy products.

The second type is provitamin A found in fruits, vegetables and other plant-based products as carotenes. Beta-carotene is the primary one out of that family of alpha carotene, gamma carotene, etc., named, of course, after the yellow-orange carroty color beta-carotene imparts.

Vitamin A has many functions in several systems and tissues. Eyes are the one most folks know. It’s essential for night vision and maintaining corneas. Somewhere between 250,000-500,000 children become blind each year in poor countries from vitamin A deficiency, which is globally the leading cause of childhood blindness.

Helping to maintain the normal covering type tissue such as skin, urethra, bowel wall is another important function of vitamin A. Deficiency causes diarrhea and death in 670,000 kids under 5 in those same developing countries.

Deficiency causes very dry and rough skin, changes in the lining of upper respiratory airways and bladder lining, and lack of tooth enamel formation. It also is crucial for immune system function, gene transcription, embryonic development and reproduction, blood cell formation in marrow, and mucous membrane integrity everywhere in us. That’s all.

Dietary sources can include cod liver oil (often parodied in movies because of its bad taste), several fish or animal livers, and dairy products for the retinol form.

For the previtamin beta-carotene, a host of vegetables supply an adequate amount if you’re willing to eat them, not just yellow or orange ones.

In the 1930s, carrot juice bars were a fad. People would go and “juice up,” downing enough to turn their skin orange. The main difference between this excessive consumption causing skin color change and “yellow jaundice” is that the eyeball whites do not turn yellow as in jaundice. Carrot juice bars are now back in style in some areas.

The recommended daily amount can be expressed as 900 micrograms (mcg) for men and 700 for women. But, the units for different vitamin As can also be expressed as recommended dietary allowances, estimated average, adequate intake, dietary reference intake, and retinol activity equivalents.

How’s that for a menu of choices and flavors? The amounts recommended vary a lot per age, gender, pregnancy and other factors.

Vitamin A has been tried as medicine for diseases, especially acne, with plus-minus results. The main drawback is toxicity from too much being stored in liver. That can cause liver failure and several other side effects including nausea, vomiting, dizziness and blurry vision for very high acute doses, especially over 200,000 mcg.

Taking more than 10,000 mcg per day long-term can cause bone thinning, bone and joint pain, liver damage and failure, headache (called pseudotumor cerebri), diarrhea, nausea, skin irritation and birth defects. That’s all.

Vitamin A earned the first alphabet letter because it was the first one discovered.

The later ones earned their letters chronologically. Recognizing vitamin A deficiency syndromes that were remedied by consuming foods filled with it, a long tale, led to its discovery.

How well I recall our then 5-year-old grandson asking me a biological question. I launched into an explanation with one adult sentence. As I began the second he said, “OK, that’s enough.” So, maybe now that’s what you’re saying?

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