encyclopedia

Beta-Carotene

Natural Sources:    

Carrot juice; sweet potatoes, dried apricots, carrots, spinach, cantaloupe, pumpkin and broccoli. Other good sources of beta-carotene and other carotenoids include: dandelion greens; fenugreek greens; dark green leafy vegetables (collards and kale); dark orange vegetables (yams and squash); Spirulina and other blue green algae; pink and red grapefruits; mango; and watermelon.    
   
  
Forms:    

Standardized natural beta-carotene capsules, tablets and liquids including beta-carotene, alpha-carotene, cryptoxanthin and lutein; 'Greens' supplements.    

     
Therapeutic Uses:    

– Acne
– AIDS
– Aging Disorders
– Alzheimer's Disease
– Antinflammatory
– Antioxidant
– Cataracts
– Cellular Regeneration
– Cleansing
– Detoxification
– Eyesight Disorders
– Heart Health Maintenance
– HIV Infection
– Immune System
– Lupus Nephritis
– Macular Degeneration
– Premenstrual Syndrome (PMS)
– Skin Problems
– Stroke Prevention
– Sunburn
– Ulcers
– Vascular Disorders
– Vitamin A Deficiency (RDA=2.3-7.8mg/day)     
     
    
Overview:    

Beta-carotene (also known as provitamin A – a primary precursor to retinol) is an extremely effective fat-soluble antioxidant that occurs abundantly in orange and green vegetables. The myriad health benefits of beta-carotene include: quenching free radicals that would otherwise destroy cells; blocking the formation of 'singlet oxygen' free radicals that damage DNA and destroy cell structure through turning fats rancid and toxic; preventing the oxidation of LDL cholesterol and other bad fats within the vascular system; preventing heart attacks and strokes; preventing arteries from clogging; rejuvenating immunity; preventing and blocking the growth of abnormal cells; protecting the brain from degenerative diseases; and fighting cataracts and macular degeneration. Beta-carotene is also converted into vitamin A within the body as needed; vitamin A is important for maintaining healthy skin and other body tissues, for proper wound healing, and for normal functioning of the eye. A ten year study done by Harvard found that by getting 50mg of carotenoids every other day (equivalent to seven good-size carrots), you can significantly reduce the risk of abnormal growths, vascular disease (particularly strokes), and cataracts. In a study to assess whether consumption of vegetables containing different carotenoids could protect against DNA damage and oxidative DNA damage, subjects consumed a low carotenoids diet for 2 weeks, followed by daily consumption of either tomato juice with 40 mg lycopene, carrot juice with 22.3 mg beta-carotene and 15.7 mg alpha-carotene, or spinach powder with 11.3 mg lutein. Supplementation resulted in a significant decrease in cellular levels of strand breaks in lymphocyte DNA but only carrot juice carotenoids significantly reduced oxidative DNA damage. Dr. Duke, in The Green Pharmacy, recommends carotenoid supplementation for those with Alzheimer's disease and HIV infection. Jean Carper, in Stop Aging Now, recommends carotenoids particularly for boosting immunity and preventing abnormal growths, vascular disease and strokes.
    
 
Chemistry:    

Carotenoids are a class of natural fat-soluble pigments found principally in plants, algae, and photosynthetic bacteria, where they play a critical role in the photosynthetic process. Plants naturally contain many different carotenoids, of which there are hundreds. For instance, carrots contain: alpha-carotene, beta-carotene, epsilon-carotene, gamma-carotene, beta-cryptoxanthin, lutein, xanthophylls and many other carotenoids. Carotenoids are defined by their chemical structure. The majority of carotenoids are derived from a 40-carbon polyene chain, which could be considered the backbone of the molecule. This chain may be terminated by cyclic end-groups (rings) and may be complemented with oxygen-containing functional groups. The hydrocarbon carotenoids are known as carotenes, while oxygenated derivatives of these hydrocarbons are known as xanthophylls. Beta-carotene, the principal carotenoid in carrots, is a familiar carotene, while lutein, the major yellow pigment of marigold petals, is a common xanthophyll. All are powerful antioxidants. The distinctive pattern of alternating single and double bonds in the polyene backbone of carotenoids is what allows them to absorb excess energy from other molecules (antioxidant activity), while the nature of the specific end groups on carotenoids may influence their biological activity thought their interaction with cell membranes.    
   
     
Suggested Amount:    

The U.S. Recommended Dietary Allowance (RDA) for beta-carotene as a source of provitamin A is 2.3-7.8mg/day. Most clinical trials with significant results used dosages of between 10mg (17,000 IU) to 30mg (50,000 IU) daily and found this level to be very safe with no toxic effects. Food sources of beta-carotene are important to have in the diet, but researchers also recommend a daily supplement of natural source beta-carotene to ensure constant therapeutic levels. Experts recommend getting preformed vitamin A (vitamin A) in dosages no greater than 5000 to 10,000 IU daily. Note: Fat-soluble vitamins, including vitamins A, E, D and K, are usually absorbed with the help of foods that contain fat. Natural food sources of beta-carotene include: Carrot juice (24.2mg/cup), sweet potatoes (10mg per medium potato), dried apricots (6.2mg in 10 halves), carrots (5.7mg per medium carrot), cooked spinach (4.9mg per cup), cantaloupe (4.0mg per 1/8th), cooked pumpkin (3.7mg per half cup), and cooked broccoli (1.0mg per half cup).
 
New International Measurements:
Until recently, vitamin A activity in foods was expressed as international units (IU). This is still the measurement generally used on food and supplement labels. However, it is difficult to calculate the total vitamin A activity in the diet in terms of IU, because both the absorption and conversion of carotenoids, as compared with retinol, are variable. In order to standardize vitamin A measurement, it has now been internationally agreed to state vitamin A activity as a new unit called retinol equivalents or RE. By definition, one retinol equivalent is equal to: 1 RE=1 ΅g retinol=6 ΅g beta-carotene=12 ΅g other provitamin A carotenoids=3.33 IU vitamin A activity from retinol=10 IU vitamin A activity from beta-carotene. [Equivalents information from: F. Hoffmann-La Roche Ltd. 2000. Vitamin A Information Sheet]. Note: To make these conversion less confusing, remember that although 1 molecule of beta-carotene is cleaved into two molecules of retinol, that beta-carotene is poorly absorbed by the gastrointestinal tract and therefore you need 6 molecules of beta-carotene to be equivalent to one molecule of retinol.
    
    
Drug Interactions:    

None known.    
     
    
Contraindications:    

None known. Synthetic beta-carotene is contraindicated in smokers. It is best to stick with carrots and/or other natural sources of carotenoids because synthetic beta-carotene supplements (100% All-trans isomer) do not confer all of the same health benefits. At least two different clinical trials of supplemental beta-carotene (using synthetic 100% All-trans isomer) for helping smokers to prevent lung disease have been stopped prior to completion due to a 27% increased risk of death from lung disease among participants.    
     
    
Side Effects:    

Beta-carotene is considered a safe form of vitamin A because the body converts it only as needed (unlike excessive vitamin A from retinol in the diet that can cause liver damage and other adverse effects). Many multi-vitamin pills supply beta-carotene because it is much safer than pre-made vitamin A. Beta-carotene is poorly absorbed from the gastrointestinal tract, and its conversion to retinol becomes progressively less efficient as vitamin A status improves. High intakes (over 30 mg/day) of beta-carotene, however, may result in an orange-yellow coloration of the skin, which is reversible upon cessation of beta-carotene intake. Italian studies using 90mg/day of beta-carotene have shown no significant signs of toxicity. Hundreds of animal studies using very high dosages of beta-carotene have also detected virtually no toxicity. Note: When using beta-carotene as a source of vitamin A, it is best to stick with natural sources of carotenoids because synthetic beta-carotene supplements (100% all-trans isomer) do not confer all of the same health benefits. At least two different clinical trials of supplemental beta-carotene (using synthetic 100% all-trans isomer) for helping smokers to prevent lung cancer have been stopped prior to completion due to a 27% increased risk of death from lung cancer among participants.

Vitamin A Deficiency Symptoms:
Vitamin A deficiency is common among the elderly and urban poor, people who abuse laxatives, and alcoholics. Deficiency of vitamin A is also still a major cause of premature death in developing nations, particularly among children. One of the early symptoms is night blindness, the inability to see in dim light. If the deficiency persists, total blindness (xerophthalmia) can occur. The appearance of skin lesions (follicular hyperkeratinosis) has also been used as an early indicator of inadequate vitamin A status. In children with xerophthalmia, concurrent problems such as stunted growth, respiratory diseases, diarrhea, and parasitic and infectious diseases are common. Diseases themselves may induce vitamin A deficiency, most notably liver and gastrointestinal diseases which interfere with the absorption and utilization of vitamin A. Poor vitamin A status is also thought to be involved in the development of cancer, although the precise mechanisms are not yet known.
    

References:     
     
Carper, J. 1995. Stop Aging Now. HarperCollins Publishers, 10 East 53rd Street, New York, New York 10022-5299. Pp. 59-67.
 
Duke, J. 1997: The Green Pharmacy, The Ultimate Compendium of Natural Remedies from the World's Foremost Authority on Healing and Herbs. Pp. 49; 50; 331. Rodale Press.
 
Gey KF. 1995. Cardiovascular disease and vitamins. Concurrent correction of 'suboptimal' plasma antioxidant levels may, as important part of 'optimal' nutrition, help to prevent early stages of cardiovascular disease and cancer, respectively. Bibl Nutr Dieta. 1995; (52): 75-91. Review.
 
Heinonen OP, Albanes D, Virtamo J, Taylor PR, Huttunen JK, Hartman AM, Haapakoski J, Malila N, Rautalahti M, Ripatti S, Maenpaa H, Teerenhovi L, Koss L, Virolainen M, Edwards BK. 1998. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J Natl Cancer Inst. 1998 Mar 18; 90(6): 440-6.
 
Van Hoydonck PG, Temme EH, Schouten EG. 2002. A dietary oxidative balance score of vitamin C, beta-carotene and iron intakes and mortality risk in male smoking Belgians. J Nutr. 2002 Apr; 132(4): 756-61.
    
    
Additional Information:    

Supplementing with Carotenoids Versus Vitamin A:
There are two ways of obtaining adequate levels of vitamin A in the diet. Pre-formed vitamin A (retinol) is found in animal products such as cod liver oil, liver, egg yolk, fish, whole milk, butter and cheese. Vitamin A is essential for health but can be toxic in excess and should be avoided from supplements in doses greater than 10,000 IU daily. However, beta-carotene and other carotenoids, sometimes referred to as vegetable vitamin A or provitamin A, can safely be obtained in the diet in high levels and the body can then covert these powerful antioxidants into retinol as needed. Dietary carotenoids, including beta-carotene, do not have the toxic potential of retinol and safely provide many health benefits. Carotenoids include yellow, orange and red pigments in plants, often masked by chlorophyll, that act as protective antioxidants. There are hundreds of carotenoids in nature; for example, the bright red color of tomatoes is attributable to the carotenoid lycopene. The orange color of carrots is due to the presence of large amounts of beta-carotene and other carotenoids. Many carotenoids can be converted within the body into vitamin A. Beta-carotene is the carotenoid with the highest provitamin A activity. Specifically, one molecule of beta-carotene can be cleaved by a specific intestinal enzyme into two molecules of vitamin A.

Clinical Trials with Natural Carotenoids Showing Positive Results:
Jean Carper, in her best selling book, Stop Aging Now, reports that three Australian studies suggest that beta-carotene blocks development of cancer of the cervix. Mega-doses of beta-carotene supplements reversed pre-cancerous lesions of the mouth in 50 to 70 percent of subjects who took it. She also notes that men with colon cancer who took 30 milligrams of beta-carotene daily had specific cancer-promoting activity in cells inhibited by 44 percent after only two weeks and 57 percent after nine weeks. Furthermore, the activity remained low even six months after the men stopped taking the beta-carotene supplements.
 
In a study to assess whether consumption of vegetables containing different carotenoids could protect against DNA damage and oxidative DNA damage, subjects consumed a low carotenoids diet for 2 weeks, followed by two weeks with the daily consumption of 330 ml tomato juice with 40 mg lycopene (weeks 3 and 4), two weeks with daily consumption of 330 ml carrot juice with 22.3 mg beta-carotene and 15.7 mg alpha-carotene (weeks 5 and 6), and, finally, two weeks with the daily consumption of 10 g dried spinach powder with 11.3 mg lutein (weeks 7 and 8). Supplementation resulted in a significant decrease in endogenous levels of strand breaks in lymphocyte DNA but only carrot juice significantly reduced oxidative DNA damage. [Watzl B, Bub A, Brandstetter BR, Rechkemmer G. 1999. Modulation of human T-lymphocyte functions by the consumption of carotenoid-rich vegetables. Br J Nutr 1999 Nov; 82(5): 383-9]. [Pool-Zobel BL, Bub A, Muller H, Wollowski I, Rechkemmer G. 1997. Consumption of vegetables reduces genetic damage in humans: first results of a human intervention trial with carotenoid-rich foods. Carcinogenesis 1997 Sep; 18(9): 1847-50].