Vitamin A, in general, refers to a fat-soluble group called all-trans-retinol and occurs naturally, primarily in the form of fatty acid esters such as vitamin A palmitate (retinyl palmitate) and the acetate form, retinyl acetate. Retinol (an alcohol) and retinal (an aldehyde) are usually referred to as preformed vitamin A. Retinol, retinal, retinoic acid, and related compounds are known as retinoids. Other names for all-trans-retinol include retinol, vitamin A1, anti-infective vitamin, and (all-E)-3, 7-dimethyl-9-(2,6,6 trimethyl-1-cyclohexen-1-y1)-2,4,6,8-nonatetraen-1-o1…no wonder we just call it vitamin A!... And there are dozens of chemical names for other minor dietary forms. Retinal is an important form because it can be converted by the body to retinoic acid (RA), the form of vitamin A known to affect gene transcription, embryonic and fetal development of limbs, heart, eyes, ears, and regulates the expression of the gene for growth hormone. Vitamin A dietary deficiency was one of the 1st noted and signs include corneal changes, xerophthalmia-a major cause of blindness in children, night blindness, GI and urinary tract epithelia, growth retardation, follicular keratosis of the skin, increased propensity to infectious diseases, and various skin conditions including acne and psoriasis. Deficiencies also occur with malabsorption syndromes, (cystic fibrosis, Whipple’s disease, Crohn’s disease, ulcerative colitis, short bowel syndrome) and result in chronic liver diseases, including cirrhosis as well as pancreatic disease.

The RDA is the minimum daily requirement (MDR) of vitamin A that maintains a 4 month reserve, which is currently set as 3,000 IU’s per day, however the USRDA for adults is 5,000 IU, but there is still much debate as to amount that is required due to disease, stress, and exercise variability with adults. Children’s value is about 1/3 of the adult value. In times of great physical, mental, chemical or disease stress, it is common to recommend 25,000 IU’s per day for 1 week and then return to normal intake with children taking about 1/3 as much. This is a case where more is not always better, but to ease your mind, studies have been done using 50,000 IU daily to resolve early stage of night blindness in 1 week!!! The literature is replete with indications for the use of vitamin A to prevent loss of vision or restore poor vision as well as documenting its anti-carcinogenic influence, immune system modulation and anti-oxidant activity. I like to refer to vitamin A as the key to maintaining cellular integrity. Just so you know, all-trans-retinoic acid is an FDA approved drug for treating acute promyelocytic leukemia (APL), so eat your fruits and veggies!

High intakes of vitamin A may manifest as dry rough skin, severe chapped or cracked lips, thinning of hair, irritability, headaches and elevated liver enzymes with a few reports of death from liver failure, however, dosing of vitamin A in the EUROSCAN study was 300,000 IU daily for 1 year and 150,000 IU daily for the 2nd year with nominal side-effects including dry skin, itching, rapid dead skin loss, bleeding and hair loss reported. Pregnant or nursing women should not exceed 5,000 IU daily without physician approval. The FDA approved drugs Colestipol, Orlistat, Cholestyramine, and mineral oil decrease the absorption of vitamin A while contraceptives may increase the serum levels of vitamin A as do the FDA approved retinoid drugs, Acitretin, All-trans-retinoic acid, isotretinoin, etretinate, and bexarotene. Consult with your physician or pharmacist if you are using the above medications. It is also important to recognize that high dosing of vitamin A will decrease the absorption of vitamin K decreasing blood clotting potential.
© 2009 W.G. Morrow, PhD, DC