Vitamin A (Retinol): A Review of Everything You Ever Needed to Know

Vitamin A (Retinol): A Review of Everything You Ever Needed to Know

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Vitamin A is a family of fat soluble vitamins that can be referred to as retinoids. This class includes retinol, retinal, and retinoic acid. You may also have heard of isotretinoin, aka accutane which is closely related to vitamin A. You also have probably heard of beta carotenes or carotenoids, and these are a precursor to Vitamin A synthesis. I’m not going to dwell on all these distinctions and differences unless I think it has a specific impact on your health, but they are definitely worth mentioning.

How your body metabolizes the compound depends on the type of vitamin A ingested. Provitamin A substances, which mostly refers to beta carotenes from plant sources, require metabolic activity which is highly regulated by the body and toxicity is unlikely. However, preformed vitamin A from supplements or animal sources is more efficient and less regulated and toxicity is possible.

Vitamin A Supplement Options: http://amzn.to/2pXSXuu

Biological Activity

Vitamin A is an essential component of properly functioning vision. It prevents xerophthalmia (dry eyes) and facilitates phototransduction. Vitamin A is also crucial to cellular differentiation and and integrity of the eye. Thus, it is an essential component of the visual cycle.

Deficiency

Although rare in the US, vitamin A deficiency is the third most common vitamin deficiency in the world. Consequently, many parts of the world have increased incidence of night blindness, complete blindness and dry eyes (xerophthalmia).

As many as 500,000 malnourished children suffer from these maladies each year around the globe. Clinical manifestations include visual deficits as previously described, poor bone growth, non specific skin problems and impaired immune system function.

Toxicity

Toxicity is possible, most often from ingesting too much vitamin A supplement. There are acute and chronic presentations which aren’t worth getting into.

I will say that retinoic acid has been shown to be harmful (teratogenic) to a growing fetus  in first trimester pregnancy when receiving doses several times the RDA. A safe upper limit for vitamin A intake during pregnancy has been recognized at about 10,000 IU daily. please talk to your obstetrician if you have concerns.

Therapeutic Uses

Measles

Vitamin A does have some therapeutic uses. Vitamin A appears to reduce the severity of symptoms in symptomatic measles cases. (Get your kids vaccinated and avoid this!)

Skin Disorders (Psoriasis, Acne)

Topical vitamin A has been used to treat a variety of skin disorders such as psoriasis and acne.

Leukemia

It’s also used to treat a specific type of blood cancer called acute promyelocytic leukemia.

Antioxidant

I will also mention that vitamin A is an antioxidant and it was investigated for prevention of cardiovascular disease. No benefits were observed. In fact, there is mixed evidence that it may actually increase the risk of cardiovascular disease as well as lung and colon cancer. Therefore, in most developed nations where vitamin A deficiency is not a common public health concern, supplementing with vitamin A is not universally recommended.

Requirements

The RDA for males is 3000 IU for males and 2300 IU for females. However, individuals with gastrointestinal disease such as crohn’s disease and cystic fibrosis may not absorb vitamin A at normal levels and may require more supplementation.

Dietary Sources

  • Retinols: liver, kidney, egg, butter
  • Beta carotenes: green vegetables, sweet potato, carrots

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