encyclopedia

Lutein

Natural Sources:
Kale, spinach, collard greens, bilberries, calendula flowers and other marigold flowers; orange peppers, tangerines, Brussels sprouts, squash, peas, corn and other vegetables and fruit.

Forms:
Standardized natural mixed-carotenoid capsules, tablets and liquids including lutein; ‘Greens’ supplements including kale, collards or spinach extracts. Bilberry extracts.

Therapeutic Uses:
– Acne
– Age-related Macular Degeneration (AMD)
– Aging Disorders
– AIDS
– Alzheimer’s Disease
– Anti-inflammatory
– Antioxidant
– Cancer Prevention
– Cataracts
– Cellular Regeneration
– Cleansing
– Detoxification
– Eyesight Disorders
– Fibromyalgia
– Heart Health Maintenance
– HIV Infection
– Immune System
– Macular Degeneration
– Skin Problems
– Stroke Prevention
– Sunburn
– Vascular Disorders
– Vitamin A Deficiency (RDA=4.6-15.6mg/day)

Overview:

utein is a carotenoid found in vegetables and fruit, particularly concentrated in green leafy vegetables such as kale, spinach and collard greens. Lutein is also concentrated in marigold petals, chlorella microalgae and to a lesser extent in bilberries. Lutein acts as an antioxidant, protecting cells against the damaging effects of free radicals. Numerous studies have documented the benefits of lutein for eye health, particularly for preventing age-related macular degeneration (AMD) and cataracts. Harvard researchers found that people with the highest consumption of lutein and zeaxanthin-rich foods lowered their risk of macular degeneration by as much as fifty-seven percent, compared to people who consumed the least amount of these foods. Dr. Yeum from Tufts University was one of the first researchers to confirm that lutein was present in the lens of the eye and confirmed earlier work that lutein and its isomer, zeaxanthin, were the only carotenoids found in eye tissues. Research has shown that lutein retards the oxidation of the lens protein which leads to cataracts. A study conducted at Harvard Medical school found that women with the highest intake of lutein and zeaxanthin had 22 percent lower risk of cataract extraction compared to those in the lowest quintile of intake. Men with the highest consumption of lutein and zeaxanthin had a 19 percent lower risk of cataract extraction compared to men with the lowest consumption. Lutein and zeaxanthin absorb near-to-UV blue light, the most damaging wavelength of light that reaches the retina. Lutein has also been found to concentrate in skin, particularly nose and facial skin, plasma and bucal mucosal cells (BMC) of the throat and in tissues of the lungs, breast, ovaries and cervix. At the University of London, researchers found that lutein applied to the skin inhibited 50 percent of erythema formation caused by a chemical irritant.

Myriad Health Benefits of Lutein:
Lutein is 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.

Chemistry:
Lutein, the major yellow pigment of marigold petals, is a common xanthophyll also found concentrated in dark green leafy vegetables. Xanthophylls are classified as carotenoids, natural fat-soluble pigments found principally in plants, algae, and photosynthetic bacteria, where they play a critical role in the photosynthetic process. Lutein and its isomer, zeaxanthin, often occur together. Other carotenoids often found with lutein include alpha-carotene, beta-carotene, gamma-carotene, beta-chryptoxanthin and lycopene. Research has shown that lutein can be converted to zeaxanthin in the blood serum and is the key carotenoid for providing the proper amount of both lutein and zeaxanthin. Zeaxanthin is itself found concentrated in peas, corn and other vegetables. 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. 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:
Nutrition experts currently recommend getting at least 6 milligrams a day of lutein (the amount found in a large bowl of spinach salad) and based on epidemiological evidence, this will reduced the risk for AMD and cataracts. As a source of provitamin A, you may want to take more than double that amount (RDA=4.6-15.6mg/day). Studies using 30mg daily of lutein have shown marked health benefits. A much lower dosage can also provide significant benefits for eye health. Researchers from Florida International University studied the effect of 2.4mg/day of lutein intake, in the form of a dietary supplement, on the serum levels and macular pigment (MP) densities over a six-month period. All subjects responded to lutein supplementation, measured by a 130% increase of lutein in the serum and most subjects increased their macular pigment density by an average increase of 14%. Increased macular pigment density has been demonstrated using spinach as a lutein-rich food and corn as a zeaxanthin-rich food, lutein dietary supplements, and bilberry extract as a low-dosage lutein supplement. Dietary intake of spinach or collard greens (which are particularly rich sources of lutein and zeaxanthin) was associated with significantly lower risk of developing AMD and cataracts. A 100mg serving of raw kale yields 40 mg of lutein and zeaxanthin, while the same quantity of cooked spinach will add 7 mg to your diet. Many of the same fruits and vegetables that are good sources of vitamin C are also good sources of lutein and zeaxanthin, such as spinach, orange peppers, tangerines, Brussels sprouts, squash, peas and corn. Chlorella is also a good source of lutein.

Drug Interactions:
None known.

Contraindications:
None known.

Side Effects:
None known.

References:

Carper, J. 1995. Stop Aging Now. HarperCollins Publishers, 10 East 53rd Street, New York, New York 10022-5299. Pp. 9, 209, 210, 252, 255.

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.

Mares-Perlman JA, Millen AE, Ficek TL, Hankinson SE. 2002. The body of evidence to support a protective role for lutein and zeaxanthin in delaying chronic disease. Overview. J Nutr 2002 Mar; 132(3): 518S-524S.

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

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:

Lutein Research:

Mares-Perlman JA, Millen AE, Ficek TL, Hankinson SE. 2002. The body of evidence to support a protective role for lutein and zeaxanthin in delaying chronic disease. Overview. J Nutr 2002 Mar; 132(3): 518S-524S.
Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison Medical School, Madison, WI 53705-2397, USA. jmaresp@facstaff.wisc.edu

Recent evidence introduces the possibility that lutein and zeaxanthin may protect against the development of the two common eye diseases of aging, cataract and macular degeneration. This potential and the lack of other effective means to slow the progression of macular degeneration have fueled high public interest in the health benefits of lutein and zeaxanthin and the proliferation of supplements containing them on pharmacy shelves. An understanding of the biologic consequences of limiting or supplementing with these carotenoids is only beginning to emerge. Some epidemiologic evidence supports a role in eye disease and, to a lesser extent, cancer and cardiovascular disease. However, the overall body of evidence is insufficient to conclude that increasing levels of lutein and zeaxanthin, specifically, will confer an important health benefit. Future advances in scientific research are required to gain a better understanding of the biologic mechanisms of their possible role in preventing disease. Additional research is also required to understand the effect of their consumption, independent of other nutrients in fruits and vegetables, on human health. The newly advanced ability to measure levels of lutein and zeaxanthin in the retina in vivo creates a unique opportunity to contribute some of this needed evidence.

Arch Ophthalmol 2002 Dec;120(12):1732-7

Lens aging in relation to nutritional determinants and possible risk factors for age-related cataract.

Berendschot TT, Broekmans WM, Klopping-Ketelaars IA, Kardinaal AF, Van Poppel G, Van Norren D.

Department of Ophthalmology, Universitair Medisch Centrum Utrecht, AZU E03.136, Heidelberglaan 100, PO Box 85500, NL-3508 GA Utrecht, the Netherlands. tosb@isi.uu.nl

OBJECTIVE: To investigate whether nutritional factors and possible risk factors for cataract influence the lens optical density (LOD). DESIGN: Three hundred seventy-six subjects, aged 18 to 75 years, were recruited. In a cross-sectional design, serum was analyzed for lutein, zeaxanthin, vitamin C, alpha-tocopherol, and cholesterol levels. Adipose tissue (n = 187) was analyzed for lutein level. The LOD and the macular pigment optical density (MPOD) were measured by spectral fundus reflectance. RESULTS: The mean +/- SD LOD at 420 nm was 0.52 +/- 0.17. It showed a significant association with age (beta =.008, P<001) and MPOD (beta = -.096, P =.02). For subjects 50 years and younger (mean +/- SD LOD, 0.45 +/- 0.11), we found only a single significant beta coefficient, for age (beta =.006, P<.001). For subjects older than 50 years (mean +/- SD LOD, 0.68 +/- 0.16), we found significant beta coefficients for age (beta =.011, P<.001) and MPOD (beta = -.240, P =.005). Controlling for age, we found no associations between LOD and other possible risk factors for age-related cataract or serum or adipose tissue concentrations of carotenoids, vitamin C, and alpha-tocopherol. CONCLUSIONS: Macular pigment is composed of lutein and zeaxanthin, the only carotenoids found in human lenses. The inverse relationship between LOD and MPOD suggests that lutein and zeaxanthin may retard aging of the lens. Clin Sci (Lond) 2002 Apr;102(4):447-56 Related Articles, Links A European multicentre, placebo-controlled supplementation study with alpha-tocopherol, carotene-rich palm oil, lutein or lycopene: analysis of serum responses. Olmedilla B, Granado F, Southon S, Wright AJ, Blanco I, Gil-Martinez E, van den Berg H, Thurnham D, Corridan B, Chopra M, Hininger I. Unidad de Vitaminas, Seccion de Nutricion, Clinica Puerta de Hierro, C/San Martin de Porres 4, 28035-Madrid, Spain. bolmedilla@hpth.insalud.es Increased levels of oxidative stress have been implicated in tissue damage and the development of chronic diseases, and dietary antioxidants may reduce the risk of oxidative tissue damage. As part of a European multicentre project, several studies were undertaken with the aim of testing whether the consumption of foods rich in carotenoids reduces oxidative damage to human tissue components. We describe here the serum response of carotenoids and tocopherols upon supplementation with carotenoids from natural extracts (alpha-carotene+beta-carotene, lutein or lycopene; 15 mg/day) and/or with alpha-tocopherol (100 mg/day) in a multicentre, placebo-controlled intervention study in 400 healthy male and female volunteers, aged 25-45 years, from five European regions (France, Northern Ireland, Republic of Ireland, The Netherlands and Spain). Supplementation with alpha-tocopherol increased serum alpha-tocopherol levels, while producing a marked decrease in serum gamma-tocopherol. Supplementation with alpha- + beta-carotene (carotene-rich palm oil) resulted in 14-fold and 5-fold increases respectively in serum levels of these carotenoids. Supplementation with lutein (from marigold extracts) elevated serum lutein (approx. 5-fold), zeaxanthin (approx. doubled) and ketocarotenoids (although these were not present in the supplement), whereas lycopene supplementation (from tomato paste) resulted in a 2-fold increase in serum lycopene. The isomer distributions of beta-carotene and lycopene in serum remained constant regardless of the isomer composition in the capsules. In Spanish volunteers, additional data showed that the serum response to carotenoid supplementation reached a plateau after 4 weeks, and no significant side effects (except carotenodermia) or changes in biochemical or haematological indices were observed throughout the study. This part of the study describes dose-time responses, isomer distribution, subject variability and side effects during supplementation with the major dietary carotenoids in healthy subjects. 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%. J Infect Dis 2000 Sep;182 Suppl 1:S11-5 Effects of lycopene and lutein supplementation on the expression of functionally associated surface molecules on blood monocytes from healthy male nonsmokers. Hughes DA, Wright AJ, Finglas PM, Polley AC, Bailey AL, Astley SB, Southon S. Diet, Health and Consumer Science Division, Institute of Food Research, Norwich Research Park, Colney, Norwich, Norfolk, NR4 7UA, UK. davida.hughes@bbsrc.ac.uk It has been suggested that dietary carotenoids can enhance immune function. Supplementation with beta-carotene (15 mg daily) was previously shown to enhance human monocyte function. To examine the effect of other dietary carotenoids, two similar independent studies were done. Healthy adult male nonsmokers were randomly assigned to receive lycopene (study 1), lutein (study 2), or placebo for 26 days, followed by the alternative treatment for another 26 days. The expression of functionally related monocyte surface molecules was quantified by laser flow cytometry before and after each treatment period. There was a significant increase in plasma levels of each carotenoid following dietary supplementation, but the effects on monocyte surface molecule expression were not as striking as those observed after beta-carotene supplementation. These findings emphasize that it cannot be assumed that the effect of one carotenoid will be the same as another, even at the same level of intake. Am J Clin Nutr 2000 May;71(5):1187-93 Amount of fat in the diet affects bioavailability of lutein esters but not of alpha-carotene, beta-carotene, and vitamin E in humans. Roodenburg AJ, Leenen R, van het Hof KH, Weststrate JA, Tijburg LB. Unilever Health Institute, Unilever Research Vlaardingen, Vlaardingen, Netherlands. annet.roodenburg@unilever.com BACKGROUND: Fat-soluble vitamin E and carotenoids are regarded as being protective against chronic diseases. Little is known about the effect of dietary fat on the bioavailability of these compounds. OBJECTIVE: The objective of this study was to assess the effect of the amount of dietary fat on plasma concentrations of vitamin E and carotenoids after supplementation with these compounds. DESIGN: During two 7-d periods, 4 groups of 14-15 volunteers received daily, with a low-fat hot meal, 1 of 4 different supplements: vitamin E (50 mg), alpha- plus beta-carotene (8 mg), lutein esters (8 mg lutein), or placebo. The supplements were provided in a low- or high-fat spread supplied in random sequence during either of the 2 experimental periods. RESULTS: As anticipated, plasma concentrations of vitamin E, alpha- and beta-carotene, and lutein were significantly higher in the supplemented groups than in the placebo group. The amount of dietary fat consumed with the hot meal (3 or 36 g) did not affect the increases in plasma concentrations of vitamin E (20% increase with the low-fat spread and 23% increase with the high-fat spread) or alpha- and beta-carotene (315% and 139% with the low-fat spread and 226% and 108% with the high-fat spread). The plasma lutein response was higher when lutein esters were consumed with the high-fat spread (207% increase) than with the low-fat spread (88% increase). CONCLUSION: Optimal uptake of vitamin E and alpha- and beta-carotene requires a limited amount of fat whereas the amount of fat required for optimal intestinal uptake of lutein esters is higher. 2000;71:-93. 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].