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| beta-carotene |
| Beta-carotene is one of almost 600 carotenoids. Fifty of these compounds have vitamin A activity. Beta-carotene may provide as much as two-thirds of the vitamin A in the human diet. Carotenoids are deposited more widely throughout the body than retinoids and are found in adipose tissues, adrenals and liver. Six carotenoids found in the highest concentrations in human serum are beta-carotene, alpha-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin. Certain carotenoids, such as beta-carotene, alpha-carotene and beta-cryptoxanthin, are dietary precursors of vitamin A, called provitamin A. Provitamin beta-carotene is found only in foods of plant origin, particularly carrots and dark leafy vegetables. Beta-carotene becomes an essential nutrient when dietary intake of retinol is inadequate. Beta-carotene functions as an antioxidant, regulator of cell communication and growth, and has shown immunomodulatory activities thought to be independent of its role as a pro-vitamin A compound. As an antioxidant, beta-carotene may quench certain free radicals and inhibit lipid peroxidation. Beta-carotene may exert anti-carcinogenic activity. Sources of beta-carotene include yellow and green leafy vegetables such as carrots, spinach, sweet potatoes, squash, and yellow fruits such as peaches and cantaloupe. There is no established recommended daily allowance (RDA) for beta-carotene. Studies of beta-carotene indicate that 6 mg/day (10,000 IU) should be adequate. One mg of beta-carotene is equivalent to 1,667 IU of beta-carotene. Chronic doses of 30 mg/day or higher of beta-carotene may cause carotenodermia. Carotenodermia is characterized by yellowish discolorization of the skin and is considered harmless and reversible with the discontinuation of beta-carotene supplementation. Supplementation of 20 mg/day or greater of beta-carotene has been linked to increased lung cancer incidence in smokers. Smokers should avoid >15 mg/day beta-carotene supplementation pending further research. If you have a sluggish thyroid (hypothyroidism), liver or kidney disease, or an eating disorder, consult your doctor before trying beta-carotene supplements. Many experts caution smokers to avoid beta-carotene supplements. The supplements are even riskier for smokers who also drink significant amounts of alcohol. If you ingest high levels of beta-carotene from either foods or supplements, the palms of your hands and the soles of your feet may turn orange. If this occurs, consult your doctor. In most cases, the coloration is harmless and will gradually fade if you reduce the amount of beta-carotene you're taking. |