Vitamin A and Beta Carotene: What, How, Where, Why Supplement?

 

Sources of Physiologic Functions:

Sources Foods rich in vitamin A include milk, cheese and butter. They also include liver and fish such as tuna, herring and sardines. The liver oils of sharks, halibuts, and polar-bears are the richest sources for vitamin A. Pre-vitamin A is abundant in spinach, carrots and papaya. Vegetable oils, white lard and white corn are poor sources of pre-vitamin and vitamin A.

Food Source

Serving Size/Amt

International Units (IUs)

Milk 2% 8 fl oz - 500IU; Cream Cheese 1oz 405IU; Cheddar Cheese 3.5 oz 1059IU; Egg (boiled) 1 medium 280IU; Egg (scrambled) 1 medium 416IU; Liver (beef braised) 3.5 oz 35679IU; Liver (veal braised) 3.5 oz 26883IU; Herring (raw) 3.o oz 80IU; Herring (kippered) 1 piece 51IU; Sardines (canned/oil) 2 pieces 54IU; Tuna (raw) 3.0 oz 50IU; Tuna (canned) 3.0 oz 16IU; Pre-Vitamin A (b-carotene) Spinach (boiled) 1/2 cup 7371IU; Spinach (raw) 1/2 cup 1880IU; Carrots (raw) 1 medium 2025IU; Carrots (boiled) 1/2 cup 19152IU; Papaya (raw) 1 medium 863IU; Oranges 1 fruit 240IU; Sweet potatoes (baked w/skin) 1 medium 24877IU; Sweet potatoes (boiled w/o skin) 1 medium 27969IU; Cantaloupes 1 cup 5158IU; Parsley 1/2 cup freeze dried 885IU

Biochemistry Vitamin A is fat-soluble. Vitamin A is the collective name for retinal (also known as retinol), retinoic acids, and b carotene. Vitamin A is mainly found in animal foods such as milk, eggs, butter and liver. A retinyl ester is a molecule retinol esterified to a palmitic or other fatty acid. The fatty acids are bound to the hydroxyl groups of retinol. The carotenoids are a rich source of pre-vitamin. In nature, there are more than 500 carotenoids. However, only 50 of these can be used to make vitamin A. The most important of these is all-trans-b-carotene. All-trans is a prefix that indicates all double bonds are trans rather than cis. Carotenoids are abundant in dark green, yellow, and orange vegetables. Cryptoxanthine, a-carotene and other forms of previtamin A include. Mammals cannot convert some carotenoids into vitamin A. This includes lutein and lycopene.

 

Vitamin A has three main functions: it supports epithelial cell growth (lung and tracheal integrity), the fetal testes and their vitality, and the cycle of vision. Only the first function can be supported by dietary retinoic acids. Retinoic Acid cannot be stored by the liver. Interconversion is possible between retinyl esters and retinol. Retinal is oxidized into retinoic acids. Dietary retinyl ester, retinol or retinal can support all three functions of vitamin. These forms can be converted into retinoic acids, but retinoic is not able to be reduced to retinal. Retinoic acid and topical creams like tretinoin are effective in treating skin problems such as acne, Darier's, psoriasis and aging.

At risk populations: In the United States, vitamin A deficiency is common among patients with chronic intestinal disease, cancer, malaria, pneumonia and anorexia. Appendectomy patients, those with burns, cirrhosis and biliary blockage have a higher requirement for vitamin A. Stress can cause excretion. A zinc and protein deficiency may decrease transport. At risk are premature infants, those with cystic fibrosis or rheumatic disease and premature babies.For more detail click here.

Signs & Symptoms: Night blindness is the first symptom. Severe vitamin A deficiencies can lead to corneal ulceration and Bitot spots. Blindness may also result. The condition is characterized by a thickening of the bones, loss of lung flexibility, epithelial Keratinization and impaired hearing. Sperm production stops in males. Fetuses are reabsorbed in females.

Safety:

It is well known that excessive intake of preformed Vitamin A can cause liver toxicity, birth defects and other adverse effects. In the age range 18-54, a daily intake of 7.500 RE (25,000IU) is considered to be safe. It took 6 years for the liver to become toxic. One report has shown toxicity at doses between 1,500-3,000 mgm (5000-10000IU), however, these results are not reproducible and contradict the majority of medical literature. No evidence exists that supplements containing 3,000 mg RE (10,001 IU) can be harmful to adults of any age. This includes pregnant women and elderly people.

Even when large quantities of beta-carotene are consumed, there is no evidence to suggest that vitamin A toxicity is caused by the conversion of beta carotene into vitamin A. High beta-carotene consumption has only ever been associated with hypercarotenemia, which is a skin coloration. Later, we will discuss the possibility that beta carotene can cause lung cancer. Two studies, ATBC and CARET, which are reviewed in all the published research on beta-carotene, suggest negative effects. All other evidence shows beta-carotene is safe.

Hypervitaminosis The early signs of hypervitaminosis include dry, irritated skin, enlarged livers, and changes in the nervous system. An increase in intracranial pressure can mimic the symptoms of brain tumors. Hypervitaminosis during pregnancy can cause malformations such as precocious growth of the skeleton and transient hydrocephalus. Other symptoms include anorexia and vomiting. Nystagmus is also a symptom, as are enlargement of lymph nodes, gingivitis or glossitis. Isotretinoin can be teratogenic, and it is contraindicated for women who are pregnant or planning to become pregnant unless the acne is unresponsive and disfiguring. Isotretinoin can cause hyperlipidemia if used for a long time. Hypervitaminosis may lead to neurotoxic vitamin effects. Hypervitaminosis can cause neurotoxic effects. Patients who receive vitamin A analogs and retinoids have reported symptoms such as headaches, pseudotumors cerebri, or embryotoxic effects. Vitamin A neurotoxicity occurs more frequently than with other vitamins because vitamin A and its analogs penetrate the CNS more effectively than other vitamins and because retinoids can have many effects upon enzyme activity and gene transcription. Megadose vitamin therapy can cause injury which is mistaken for disease symptoms. After 49 months, the study found that retinol consumption caused an increase of alkaline-phosphatase of 7%, an increase of triacylglycerol of 11%, and a decrease of HDL of 1%. Participants were randomly assigned either retinol (7 576 equivalents of retinol RE or 25,000 IU daily) or a control. As a 1% rise in cholesterol levels has been linked to a 2% risk of coronary artery diseases, the long-term ingestion 7,576 RE Vitamin A should be taken with caution.

Too much vitamin A can increase your risk for osteoporosis. Two studies found that daily vitamin A intakes > 1.5 mg led to a 6% reduction in bone density, and doubled hip fracture risk. This vitamin can weaken the bones by increasing their rate of resorption.

Periconceptional

Vitamin A is necessary for normal development and reproduction. In a single study, doses > 10,000 IU/d of vitamin A supplements were reported to cause malformations. Data from nonhuman primates show that doses up to 30,000 IU/d are not teratogenic. It is recommended that women who live in industrialized nations or have a nutritionally adequate diet not take more than RDA for preformed Vitamin A. Multiple animal studies support that there is a very low risk if unintentional periconceptional exposures of up to 30,000IU/d (9,000mg RE/d) vitamin A occur. Multiple species have been exposed to high beta-carotene doses without teratogenicity or vitamin A toxicity.