Vitamin A (fat soluble) is the term used for related compounds that are either:
1. Retinoids (Retinol is an alcohol, retinal is an aldehyde that we convert in our bodies to retinoic acid).
2. Carotenoids like B-Carotene that we convert in our bodies to retinol (plants make 100’s of these, 10% of which we can use).
Vitamin A is known to boost the immune system;
– for activation of the T lymphocytes, and for differentiation of white blood cells, helping us fight viral infections,
– is required for the integrity of the mucosal cells lining the airways, digestive tract and urinary tract
Vitamin A is essential for growth and development, especially fetal development for proper formation of limbs, heart, eyes, and ears. It is involved in cell differentiation, like stem cells becoming red blood cells and bone development, and has been found to regulate the expression of genes, like the gene for growth hormone. Vitamin A is also important for the integrity of the skin.
SYMPTOMS OF DEFICIENCY
1. Loss of vision. Dry eyes and the loss of night vision is first, with vitamin A deficiency being the leading cause of preventable blindness worldwide.
2. Increased infections (acquired immunodeficiency). Measles, respiratory infections, diarrhea, transmission of HIV, etc., all increase when deficient.
3. Reduced cancer risk (complex and seems to apply to Carotenoids but not preformed Retinoids, and high doses of Retinoids increase risk).
Animal sources (the best being cod liver oil, then liver, eggs, and dairy) provide retinyl palmitate, a precursor and storage form of retinol.
Plant sources provide the safer forms as alpha-carotene (carrots) and mostly beta-carotene (sweet-potatoes, carrots, cantaloupe, spinach, and kale).
Notice that to get the equivalent of 1 microgram of retinol, it takes:
– 1 microgram of dietary or supplemental vitamin A
– 2 micrograms of supplemental B-carotene
– 12 micrograms of dietary B-carotene
– 24 micrograms of dietary alpha-carotene or beta-crytoxanthin
Table: Selected Food Sources of Vitamin A
|Food||mcg RAE perserving||IU perserving||PercentDV*|
|Sweet potato, baked in skin, 1 whole||1,403||28,058||561|
|Beef liver, pan fried, 3 ounces||6,582||22,175||444|
|Spinach, frozen, boiled, ½ cup||573||11,458||229|
|Carrots, raw, ½ cup||459||9,189||184|
|Pumpkin pie, commercially prepared, 1 piece||488||3,743||249|
|Cantaloupe, raw, ½ cup||135||2,706||54|
|Peppers, sweet, red, raw, ½ cup||117||2,332||47|
|Mangos, raw, 1 whole||112||2,240||45|
|Black-eyed peas (cowpeas), boiled, 1 cup||66||1,305||26|
|Apricots, dried, sulfured, 10 halves||63||1,261||25|
|Broccoli, boiled, ½ cup||60||1,208||24|
|Ice cream, French vanilla, soft serve, 1 cup||278||1,014||20|
|Cheese, ricotta, part skim, 1 cup||263||945||19|
|Tomato juice, canned, ¾ cup||42||821||16|
|Herring, Atlantic, pickled, 3 ounces||219||731||15|
|Ready-to-eat cereal, fortified with 10% of the DV for vitamin A, ¾–1 cup (more heavily fortified cereals might provide more of the DV)||127–149||500||10|
|Milk, fat-free or skim, with added vitamin A and vitamin D, 1 cup||149||500||10|
|Baked beans, canned, plain or vegetarian, 1 cup||13||274||5|
|Egg, hard boiled, 1 large||75||260||5|
|Summer squash, all varieties, boiled, ½ cup||10||191||4|
|Salmon, sockeye, cooked, 3 ounces||59||176||4|
|Yogurt, plain, low fat, 1 cup||32||116||2|
|Pistachio nuts, dry roasted, 1 ounce||4||73||1|
|Tuna, light, canned in oil, drained solids, 3 ounces||20||65||1|
|Chicken, breast meat and skin, roasted, ½ breast||5||18||0|
SAFETY AND TOXICITY
Vitamin A is the most common vitamin to cause toxicity from over supplementation. Since it is fat soluble, it can accumulate in the body when given as vitamin A (Retinoids) in quantities in excess of 8,000-10,000 micrograms/day or 25,000 to 33,000 IU/day (for adults) over a long period of time.
Toxicity is often called hypervitaminosis A, with symptoms that may include nausea, loss of appetite, headaches and dizziness, dry skin, bone and joint and gait problems and in severe cases liver damage, hemorrhage and coma. You will not have toxicity when using beta-carotene or getting your vitamin a from natural food sources.
Tolerable Upper Limits for Preformed Vitamin A (retinol):
Infants-age 3: 600 micrograms (2000 IU)
4-8 years: 900 micrograms (3000 IU)
9-13 years: 1700 micrograms (6000 IU)
Teens & adults:3000 micrograms (10,000 IU)
Pregnancy: 800 micrograms (2600 IU)
Excess preformed vitamin A (Retinoids) have been known to cause birth defects, hence the recommendations for the reduced intake amounts during pregnancy and one should not use Acutane (isotretinoin) or Tretinoin (Retin-A) when you may become pregnant.
There seems to be no risk and huge benefits to taking natural Carotenoids, so eat your sweet potatoes, carrots, cantaloupes, greens, squashes, etc. in large quantities – beginning with your 4 month old infant and daily for life. Clearly, if you eat ample amounts of these nutritious vegetables, you can add huge health protective benefits in improved immunity, growth and cancer prevention.
For my thoughts on taking vitamins in general see my related blog post here…
Learn more about Vitamin A here…
You may also find the book: “An Evidence-based Approach to Vitamins and Minerals” by Jane Higdon Ph.D. a good resource.