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Lutein: A Conditionally Essential Carotenoid

A Feel 21, Inc. Health Report

By C. Leigh Broadhurst, Ph.D.

Carotenoids are named after carrots, because they impart a characteristic deep orange color to these root vegetables. There are more than 600 carontenoids found in nature, and about 50 of these are consumed in appreciable quantities in our diet. Orange, yellow, and red fruits and vegetables such as squash, apricots, peppers, mangoes, tomatoes, and pumpkin are particularly rich in carotenoids. Carotenoids also occur in green produce, but the green pigment of chlorophyll masks them. In autumn, when the leaves of deciduous trees die, the chlorophyll fades and the brilliant colors of the carotenoids are revealed. Carotenoids are most valued for their antioxidant properties, but they also are involved in cell-to-cell communication and cell growth.1,2 In addition some, most notably beta-carotene, can be converted to vitamin A by our bodies.

All carotenoids have 40 carbon structures composed of linked isoprene (2-methulbutadiene) units, and are derivatives of the most fundamental carotenoid known as lycopene. Carotene-type carotenoids contain no oxygen; examples are alpha- and beta-carotene, and lycopene. Xanthophyll-type carotenoids contain at least one oxygen group; examples are lutein, zeaxanthin, beta-cryptoxanthin, and canthaxanthin. Lutein and zeaxanthin are found in the eye, and like vitamin A, appear to play a crucial role in vision. In fact, a convincing argument can be made that although lutein has no vitamin A activity, it is nonetheless a conditionally essential nutrient.

LUTEIN AND VISION

Within the primate eye, lutein, zeaxanthin (a stereoisomer), and meso-zeaxanthin are deposited in the lens and the macula lutea. The macula lutea is the central yellow area of the retina, responsible for straight-ahead, high acuity vision. Activities such as driving, reading, hitting a ball, and recognizing facial features require sharp macular vision. The lutein and zeaxanthin in human tissues are entirely of dietary origin - they can not be synthesized. Meso-zeanthin is thought to be formed from lutein. If these carotenoids are lacking in the diet, then they are lacking in the body. In all primates, including humans, lutein is thought to function like it does in plants, primarily as a filter of shorter wavelength (higher energy) blue light, and secondarily as an antioxidant that quenches sunlight-induced reactive oxygen species.2-5

Age-related macular degeneration (AMD) is the leading cause of vision loss in elder adults and Western countries. Epidemiological evidence suggests that greater lutein consumption reduces the risks for AMD and cataracts. Further, intervention with supplementation may slow the progress of these diseases once they are established.5 In a 12-month controlled trial conducted at a Chicago area Veterans Administration Hospital, 90 male patients received 10 mg lutein per day, 10 mg lutein plus antioxidant and vitamin supplements, or placebo. In both lutein groups, macular pigment optical density increased, and the subject's visual acuity and contrast sensitivity improved compared to placebo.7,8

Macular degeneration can strike before age 50, resulting in devastating vision loss during prime adult working years. It has been hypothesized that early-onset AMD could be associated with poor absorption of lutein and zeaxanthin, but this has not proven to be the case. Seven ARM patients and six age-matched controls were supplemented with 20 mg lutein ester (equivalent to 10 mg free lutein) for 18-20 weeks. Blood plasma lutein concentration increased from a baseline concentration of 182 to a peak of 1077 nanograms/ml in AMD patients, and from 152 to 1110 nanograms/ml in control subjects, demonstrating that good absorption was attained in all subjects. Macular pigment optical density increased significantly and equally in both groups, further demonstrating that AMD does not result from poor carotenoid absorption. Evidently, lutein supplementation benefits the eyes of persons whether they have AMD or not.8

The lens of the eye also contains high levels of the antioxidant vitamins C and E. It has been clearly shown that (a) lower intakes of C, E, carotenoids, and B vitamins are strongly associated with greater risk for cataract; and (b) a 10-year history of C supplementation reduces the chance that cataracts will develop by 64 percent.9 But lutein has a unique, specific role in preventing cataracts as demonstrated in a head-to-head comparison with vitamin E (alpha-tocopherol).

In a controlled study, 17 patients with age-related cataracts were supplemented with 15 mg lutein, 100 mg vitamin E, or placebo three times per week for up to two years. Visual acuity and glare sensitivity improved with lutein supplementation, whereas there was no change with vitamin E, and a trend toward decreasing visual acuity with placebo.10 Most researchers agree that the intake of lutein as well as other nutrients relevant to eye health should be increased in the population overall, beginning early in life. Supplements cannot reverse vision loss due to AMD or cataracts, but they can stabilize these conditions and prevent full blindness. Further, AMD and cataracts can be prevented or deferred with at least a decade of appropriate nutritional intervention.

CORONARY ARTERY DISEASE AND CANCER

Several epidemiological studies have found reduced incidence of coronary artery disease (CAD), heart attack, and stroke with higher intakes of carotenoids. Within the framework of epidemiology the only firm conclusion that can be drawn is that higher intake of fruits and vegetables protects against cardiovascular disease - no surprise to you.

Unlike the hydrocarbon carontenoids which are mainly found in the LDL ("bad") cholesterol fraction, zanthophylls are incorporated into both HDL and LDL cholesterol, leading some to conclude that they help prevent harmful oxidation of cholesterol, a necessary first step in the formation of plaques on the arterial walls.4,6,11 There is no research linking lutein alone to cardiovascular disease prevention.

In the Harvard Nurses' Health Study, one of the largest epidemiological studies ever performed, 73, 286 female nurses completed a questionnaire about their diets. After a 12-year follow-up, there were 998 CAD cases. There was reduced risk for CAD among those in the top 20 percent of carotenoid intake. With respect to individual carotenoids, the risk reduction could be related to increased intakes of beta-carotene and alpha-carotene, but no significant relation with intakes of lutein, zeaxanthin, lycopene, or beta-cryptoxanthin was observed.12 Over 13 years, the corresponding Harvard Physicians' Health Study found no protective effect for heart attack from higher blood levels of alpha- and beta-carotene, beta-cryptoxanthin, lutein, lycopene, vitamin A, or vitamin E in male doctors.13

Certain antioxidants may counteract or prevent skin damage induced by ultraviolet (solar UV) radiation, because reactive oxygen species are formed in the skin from intense UV light exposure. Mice fed dietary lutein had much less ear swelling when exposed to UV-B radiation than mice fed a standard laboratory diet. Mice were also exposed to UV-B radiation for times daily and had irritating chemicals put on their skin. Their skin was less irritated by the combination of the UV and chemicals, and generated fewer reactive oxygen species when they were fed lutein. When UVB radiation was given at a single dose, no effect of lutein supplementation was observed.14

In a model of human skin behavior, genetically hairless mice were fed a lutein- and zeaxanthin-enriched diet for two weeks or a standard diet. They were then exposed to single dose of UVB radiation. Those fed the xanthophylls had reduced acute inflammation and swelling of the skin induced by the "sunburn," and reduced proliferation of skin cells in the few days following UV exposure. Cleary oral lutein makes its way to the skin to help protect it from higher energy light just as it protects the eyes.15

ABSORPTION ISSUES

Carotenoids in our diets come from vegetables, fruits, and herbs, which are low in fat - however, carotenoids are fat-soluble phytochemicals, so it's necessary to eat some fat along with these foods in order to absorb carotenoids efficiently. However, it's too simplistic to suggest that carotenoids are simply absorbed on the "coattails" of dietary fat. Absorption requires the activation of specific biochemical processes, and individuals must be able to digest fats properly.1,2

Recently at the U.S. Department of Agriculture's (USDA) Beltsville, MD and Tufts University (Boston) Research Centers, special high-lutein eggs were found to have superior lutein bio-availability compared to spinach or supplements. The chickens were fed marigold petals to increase lutein in their eggs. I's hypothesized that lecithin in the egg yolk positively influences carotenoid bio-availability.9

Furthermore, release of carotenoids from plant cells may require cooking, pureeing, or fine chopping. Efforts are underway at the USDA to develop high-xanthophyll carrots and potatoes to improve consumer access to these carotenoids. If lutein is taken in supplemental form, either alone or in mixed carotenoid supplement, the capsules should be taken with a meal or snack, not on an empty stomach or with only juice or coffee, etc. VR


REFERENCES

  1. Furr HC, Clark Rm (1997). Intestinal absorption and tissue distribution of carotenoids. Journal of Nutritional Biochemistry 8, 364-377.
  2. Bell EA, Charlwood BV (eds). (1980). Secondary Plant Products. Berlin, Springer-Verlag.
  3. Alves-Rodrigues A, Shao A (2004). The science behind lutein. Toxicol Lett 150, 57-83.
  4. Granado F, Olmedilla B, Blanco I (2003). Nutritional and clinical relevance of lutein in human health. Br J Nutr 90, 487-502.
  5. Krinsky NI, Landrum JT, Bone RA (2003). Biologic mechanisms of the protective role of lutein and zeaxanthin in the eye. Annu Rev Nutr 23, 171-201.
  6. 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 Nutr132 518S-524S
  7. Koh HH, Murray IJ, Nolan D et al. (2004). Plasma and macular responses to lutein supplement in subjects with and without age-related maculopathy: a pilot study. Exp Eye Res 79, 21-27.
  8. Richer S, Stiles W, Statkute L et al. (2004). Double-masked, placebo-controlled, randomized trial of lutein and antioxidant supplementation in the intervention of atrophic age-related macular degeneration: the Veterans LAST study (Lutein Antioxidant Supplementation Trial). Optometry 75, 216-230.
  9. Bliss RM (2003). Scientists link nutrition and eye health. Agricultural Research 51, 8 (Aug), 4-7.
  10. Olmedilla B, Granado F, BlancoI, Vaquero M (2003). Lutein, but not alpha-tocopherol, supplementation improves visual function in patients with age-related cataracts: a 2-y double-blind, placebo-controlled pilot study. Nutrition 19, 21-24.
  11. Dwyer JH, Navab M, Dwyer KM et al. (2001). Oxygenated carotenoid lutein and progression of early atherosclerosis: the Los Angeles atherosclerosis study. Circulation 10., 2922-2927.
  12. Osganian SK, Stampfer MJ, Rimm E, et al. (2003). Dietary carotenoids and risk of coronary artery disease in women. Am J Clin Nutr 77, 1390-1399.
  13. Hak AE, Stamfer MJ, Campos H, et al. (2003). Plasma carotenoids and tocopherols and risk of myocardial infarction in a low-risk population of US male physicians. Circulation 108,802-807.
  14. Lee EH, Faulhaber D, Hanson KM et al. (2004). Dietary lutein reduces ultraviolet radiation-induced inflammation and immunosuppression. J Invest Dermatol 122, 510-517.
  15. Gonzalez S, Astner S, An W. Goukasian D, Panthak MA (2003). Dietary lutein/zeaxanthin decreases ultraviolet B-induced epidermal hyperproliferation and acute inflammation in hairless mice. J Invest Dermatol 121, 399-405.

  16. VITAMIN RETAILER August 2004
    Lutein: A Conditionally Essential Carotenoid
    By C. Leigh Broadhurst, Ph.D.
    Pages 36, 38


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