encyclopedia

Carotenoids

Natural Sources:    

Carrot juice; tomato juice, sweet potatoes, dried apricots, carrots, tomatoes, spinach, cantaloupe, pumpkin and broccoli. Other good sources of 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 mixed-carotenoid capsules, tablets and liquids including beta-carotene, lycopene, alpha-carotene, chryptoxanthin and lutein; 'Greens' supplements.    
     

Therapeutic Uses:    

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

Carotenoids are a class of natural fat-soluble pigments that give many fruits and vegetables their yellow, orange and red color. Plants naturally contain many different carotenoids, of which there are hundreds. Tomatoes are rich in lycopene, while carrots and spinach are rich in alpha-carotene, beta-carotene, lutein, and xanthophylls. The most abundant and best known of the carotenoids is beta-carotene. Carotenoids are precursors of vitamin A and are also called “provitamin A” or vegetable-source vitamin A; their vitamin A activity occurs only upon conversion to retinol within the body. Beta-carotene is one of the most active of carotenes as a source of vitamin A.  One molecule of beta-carotene can be cleaved by a specific intestinal enzyme into two molecules of vitamin A. However, because carotenoids are not as readily absorbed as retinol within the stomach, it actually takes six molecules of beta-carotene to produce one molecule of retinol. All carotenoids are powerful antioxidants and are known to significantly reduce the risk of cancer. Beta-carotene has established antitumor and immune-enhancing activity. Unlike vitamin A, high doses of carotenoids do not possess significant toxicity. As a source of vitamin A, carotenoids are most well known for their benefits for the eyes. As a source of vitamin A, carotenoids are also beneficial for the formation and maintenance of skin, hair, and mucous membranes. Carotenoids help people with night-blindness to see in dim light and are beneficial for proper bone growth, tooth development, and reproduction. Carotenoids, as a source of Vitamin A and its analogues, also favorably influence differentiation and proliferation of cells, thwart cancer and strengthen immune responses. Research has shown that a diet rich in natural carotenoids and other plant nutrients is beneficial for treating fibromyalgia, age-related macular degeneration and reducing the adverse effect of HIV-1, malaria, and diarrheal infections on child growth.
    
    
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 including alpha-carotene, beta-carotene, epsilon-carotene, gamma-carotene, beta-cryptoxanthin, lutein, lycopene, 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).

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.

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.
    
   
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.
 

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.
   
   
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.
 
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
 
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.
 
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
    
    
Additional Information:    

Myriad Health Benefits of Carotenoids:
The myriad health benefits of carotenoids include: 1) quenching free radicals that would otherwise destroy cells; 2) specifically blocking the formation of 'singlet oxygen' free radicals that damage DNA and destroy cell structure through turning fats rancid and toxic; 3) preventing the oxidation of LDL cholesterol and other bad fats within the vascular system; 4) preventing heart attacks and strokes; 5) preventing arteries from clogging; 6) rejuvenating immunity; 7) preventing and blocking the growth of abnormal cells; 8) protecting the brain from degenerative diseases; and 9) fighting cataracts and macular degeneration. Carotenoids are also beneficial for maintaining healthy skin and other body tissues and for proper wound healing. 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.

Sackett CS, Schenning S. 2002. The age-related eye disease study: the results of the clinical trial. Insight 2002 Jan-Mar; 27(1): 5-7.
 
The Age-Related Eye Disease Study (AREDS) is a multi-center study sponsored by the National Eye Institute to determine the natural history and risk factors associated with both cataract and age-related macular degeneration (AMD). AREDS incorporated a clinical trial to determine what role micro nutrients may play in the development and progression of cataracts and AMD. The micro nutrients studied were the antioxidants vitamins E,C, beta-carotene and zinc with copper. Participants were randomized to either antioxidants, mineral, a combination of antioxidants and minerals or placebo. The participants were categorized, by the presence of drusen and diagnosis of AMD into one of four groups: no AMD, early AMD, intermediate AMD or advanced AMD. They were followed for an average of 6.3 years. In the AMD trial groups, those at high risk of developing advanced AMD lowered their risk by about 25% when treated with the mega dosages of the combination of antioxidants and minerals. There was no statistically significant difference in the cataract trial between treatment and placebo. [Wilmer Institute Woods, 265 600 North Wolfe Street, Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA].
 
Natural Beta-carotene Research:

Donaldson MS, Speight N, Loomis S. 2001. Fibromyalgia syndrome improved using a mostly raw vegetarian diet: An observational study. BMC Complement Altern Med 2001; 1(1): 7.
 
BACKGROUND: Fibromyalgia engulfs patients in a downward, reinforcing cycle of unrestorative sleep, chronic pain, fatigue, inactivity, and depression. In this study we tested whether a mostly raw vegetarian diet would significantly improve fibromyalgia symptoms.
METHODS: Thirty people participated in a dietary intervention using a mostly raw, pure vegetarian diet. The diet consisted of raw fruits, salads, carrot juice, tubers, grain products, nuts, seeds, and a dehydrated barley grass juice product. Outcomes measured were dietary intake, the fibromyalgia impact questionnaire (FIQ), SF-36 health survey, a quality of life survey (QOLS), and physical performance measurements.
RESULTS: Twenty-six subjects returned dietary surveys at 2 months; 20 subjects returned surveys at the beginning, end, and at either 2 or 4 months of intervention; 3 subjects were lost to follow-up. The mean FIQ score (n = 20) was reduced 46% from 51 to 28. Seven of the 8 SF-36 subscales, bodily pain being the exception, showed significant improvement (n = 20, all P for trend < 0.01). The QOLS, scaled from 0 to 7, rose from 3.9 initially to 4.9 at 7 months (n = 20, P for trend 0.000001). Significant improvements (n = 18, P < 0.03, paired t-test) were seen in shoulder pain at rest and after motion, abduction range of motion of shoulder, flexibility, chair test, and 6-minute walk. 19 of 30 subjects were classified as responders, with significant improvement on all measured outcomes, compared to no improvement among non-responders. At 7 months responders' SF-36 scores for all scales except bodily pain were no longer statistically different from norms for women ages 45-54.
CONCLUSION: This dietary intervention shows that many fibromyalgia subjects can be helped by a mostly raw vegetarian diet. [Hallelujah Acres Foundation, Shelby, NC USA. michael@hacres.com].
 
Ren H, Endo H, Hayashi T. 2001. The superiority of organically cultivated vegetables to general ones regarding antimutagenic activities. Mutat Res 2001 Sep 20; 496(1-2): 83-8.
 
Department of Food Science and Technology, Tokyo University of Fisheries, Minato-ku, 108-8477, Tokyo, Japan.
 
We found organically cultivated (OC) vegetables, using a water-soluble chitosan as a soil improvement agent and leaf surface spray, had much longer shelf life and better taste than that of generally cultivated (GC) vegetables. The purpose of this study is to determine the relative antimutagenic activity between OC and GC vegetables. Eleven OC vegetables were harvested in March and April in 1999 and 2000, and GC ones were supplied as a control from nearby farms on the same date. The former vegetables were planted on the field where no pesticide had been used for the last 3 years. Forward mutation test with Salmonella typhimurium TM677 and 8-azaguanine as a detection agent was used to determine the antimutagenic activity of juices prepared from OC and GC vegetables against authentic mutagens, such as 4-nitroquinoline oxide (4NQO), benzo(a)pyrene (BaP), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-P-2). This microbiological test is a convenient method to use for the food samples containing free histidine. Antimutagenic activity was evaluated by the difference of mutagenic activities between mutagenecity of authentic compounds and that observed upon incubation at 37 degrees C for 2h with each vegetable juice. OC Chinese cabbage, carrot, Welsh onion, and Qing-gen-cai suppressed 37-93% of the mutagenic activity of 4NQO, while the GC ones were held down to 11-65%. Against BaP, three species of OC vegetables showed 30-57% antimutagenecity, while GC ones did only 5-30%. Similarly, the OC spinach decreased the activity of Trp-P-2 to 78%, and the GC suppressed it by 49%.
 
Karakaya S, El SN, Tas AA. 2001. Antioxidant activity of some foods containing phenolic compounds. Int J Food Sci Nutr 2001 Nov; 52(6): 501-8.
 
This study was designed to determine the total phenols (TP) and total antioxidant activity (TAA) of some liquid and solid plant foods that are commonly consumed in Turkey. Total phenols were analysed according to the Folin-Ciocalteu method and antioxidant activities of these compounds in aqueous phase were assessed by measuring their direct ABTS.- radical scavenging abilities. Total phenols varied from 68 to 4162 mg/l for liquid foods and from 735 to 3994 mg/kg for solid foods. TAA of liquid and solid foods ranged between 0.61-6.78 mM and 0.63-8.62 mM, respectively. Total antioxidant activities of foods were well correlated with total phenols (r2 = 0.95). According to content of total phenols per serving, liquid foods were in the order of black tea > instant coffee > coke > red wine > violet carrot juice > apricot nectar > Turkish coffee > grape molasses > sage > white wine > linden flower, and solid foods were in the order of red grape > raisins > tarhana > dried black plum > dried apricot > grape > fresh paprika > fresh black plum > Urtica sp. > cherry > fresh apricot > paprika pickle > paprika paste.  [Ege University, Engineering Faculty, Food Engineering Department, 35100, Bornova, Izmir, Turkey].

Moller P, Loft S. 2002. Oxidative DNA damage in human white blood cells in dietary antioxidant intervention studies. Am J Clin Nutr 2002 Aug; 76(2): 303-10.
 
Many epidemiologic studies have addressed the possible preventive effects of antioxidants in disease causation and progression. With the use of molecular techniques, it is feasible to investigate specific properties of antioxidants in intervention studies. The most widely used techniques to investigate oxidative DNA damage in white blood cells are the measurement of 7-hydroxy-8-oxo-2'-deoxyguanosine and the comet assay. The types of antioxidant intervention studies include those involving single or multiple supplementations of vitamin C, vitamin E, or carotenoids and those involving various natural food products (eg, carrot juice). In short-term intervention studies (usually weeks or a few months), results have been mixed. Single-dosing studies found that decreased oxidative DNA damage lasted only hours after antioxidant supplementation, suggesting that the preventive effect is relatively short. In addition, many of the positive studies were not placebo-controlled, thus leaving a possibility of false-positive results caused by period effects, eg, seasonal variation, changes in the lifestyles of the subjects, or variation in measurements over time. Because participation in an antioxidant intervention study may cause changes in dietary habits and because seasonal changes may have profound effects, it is recommended that future studies have a placebo-controlled, parallel design rather than a crossover design. [Institute of Public Health, The Panum Institute, University of Copenhagen, Denmark. fipm@farmakol.ku.dk].
 
Thurmann PA, Steffen J, Zwernemann C, Aebischer CP, Cohn W, Wendt G, Schalch W. 2002. Plasma concentration response to drinks containing beta-carotene as carrot juice or formulated as a water dispersible powder. Eur J Nutr 2002 Oct; 41(5): 228-235.
 
BACKGROUND: Bioavailability of beta-carotene is highly variable and depends on the source, the formulation and other nutritional factors.
OBJECTIVE: It was the aim of the study to compare beta-carotene plasma response to b-carotene dosing with two commercially available drinks, containing beta-carotene from carrot juice or as water dispersible beta-carotene powder. Design In a randomized, parallel group study design, 4 volunteers per group received daily beta-carotene doses of 6-7 or 18-22 mg of either drink over 6 weeks. Blood samples for determination of carotenoid and vitamin A plasma concentrations were collected before supplementation and over the dosing period.
RESULTS: Apparent steady-state beta-carotene concentrations were attained after 40 days of supplementation. Consumption of the beverage containing beta-carotene as a water dispersible powder resulted in a higher response of beta-carotene plasma concentrations with increments of 3.84 +/- 0.60 &mgr;mol/L (p < 0.05, dose: 7.2 mg/d) and 5.04 +/- 0.72 &mgr;mol/L (p < 0.05, dose: 21.6 mg/d), respectively, in comparison to the carrot juice-based drink with increments of 0.42 +/- 0.33 &mgr;mol/L (dose: 6 mg/d) and 1.71 +/- 0.55 &mgr;mol/L (dose: 18 mg/d), respectively. beta-carotene was cleared from the plasma with an apparent half-life of 6-11 days. Plasma concentrations of alpha-carotene, beta-cryptoxanthin, lutein, zeaxanthin, and lycopene remained almost unchanged, whereas retinol plasma concentrations increased slightly. By contrast, with the exception of elevated 13-cis-retinoic acid in one group (21.6 mg/d, water dispersible powder), the concentrations of all-trans-retinoic acid, and the oxo-derivatives or retinoic acid were not significantly affected by b-carotene supplementation.
CONCLUSIONS: The results confirm that the relative bioavailability of beta-carotene depends largely on the source of b-carotene and demonstrate the superior bioavailability of beta-carotene powder in comparison to that in carrot juice. [Philipp Klee-Institute of Clinical Pharmacology, Hospital Wuppertal GmbH, Heusnerstr. 40, 42283 Wuppertal, Germany. petra.thuermann@klinikum-wuppertal.de].

External 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. 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 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. 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