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      Serum and macular response to carotenoid-enriched egg supplementation in human subjects: the Egg Xanthophyll Intervention clinical Trial (EXIT)

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          Abstract

          The macular carotenoids lutein (L), zeaxanthin (Z) and meso-zeaxanthin (MZ) accumulate at the macula, where they are collectively referred to as macular pigment (MP). Augmentation of this pigment, typically achieved through diet and supplementation, enhances visual function and protects against progression of age-related macular degeneration. However, it is known that eggs are a rich dietary source of L and Z, in a highly bioavailable matrix. In this single-blind placebo-controlled study, L- and MZ-enriched eggs and control non-enriched eggs were fed to human subjects (mean age 41 and 35 years, respectively) over an 8-week period, and outcome measures included MP, visual function and serum concentrations of carotenoids and cholesterol. Serum carotenoid concentrations increased significantly in control and enriched egg groups, but to a significantly greater extent in the enriched egg group ( P<0·001 for L, Z and MZ). There was no significant increase in MP in either study group post intervention, and we saw no significant improvement in visual performance in either group. Total cholesterol increased significantly in each group, but it did not exceed the upper limit of the normative range (6·5 mmol/l). Therefore, carotenoid-enriched eggs may represent an effective dietary source of L, Z and MZ, reflected in significantly raised serum concentrations of these carotenoids, and consequentially improved bioavailability for capture by target tissues. However, benefits in terms of MP augmentation and /or improved visual performance were not realised over the 8-week study period, and a study of greater duration will be required to address these questions.

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          The role of oxidative stress in the pathogenesis of age-related macular degeneration.

          Age-related macular degeneration (AMD) is the leading cause of blind registration in the developed world, and yet its pathogenesis remains poorly understood. Oxidative stress, which refers to cellular damage caused by reactive oxygen intermediates (ROI), has been implicated in many disease processes, especially age-related disorders. ROIs include free radicals, hydrogen peroxide, and singlet oxygen, and they are often the byproducts of oxygen metabolism. The retina is particularly susceptible to oxidative stress because of its high consumption of oxygen, its high proportion of polyunsaturated fatty acids, and its exposure to visible light. In vitro studies have consistently shown that photochemical retinal injury is attributable to oxidative stress and that the antioxidant vitamins A, C, and E protect against this type of injury. Furthermore, there is strong evidence suggesting that lipofuscin is derived, at least in part, from oxidatively damaged photoreceptor outer segments and that it is itself a photoreactive substance. However, the relationships between dietary and serum levels of the antioxidant vitamins and age-related macular disease are less clear, although a protective effect of high plasma concentrations of alpha-tocopherol has been convincingly demonstrated. Macular pigment is also believed to limit retinal oxidative damage by absorbing incoming blue light and/or quenching ROIs. Many putative risk-factors for AMD have been linked to a lack of macular pigment, including female gender, lens density, tobacco use, light iris color, and reduced visual sensitivity. Moreover, the Eye Disease Case-Control Study found that high plasma levels of lutein and zeaxanthin were associated with reduced risk of neovascular AMD. The concept that AMD can be attributed to cumulative oxidative stress is enticing, but remains unproven. With a view to reducing oxidative damage, the effect of nutritional antioxidant supplements on the onset and natural course of age-related macular disease is currently being evaluated.
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            Age-related macular degeneration is the leading cause of blindness...

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              Lutein, zeaxanthin, and the macular pigment.

              The predominant carotenoids of the macular pigment are lutein, zeaxanthin, and meso-zeaxanthin. The regular distribution pattern of these carotenoids within the human macula indicates that their deposition is actively controlled in this tissue. The chemical, structural, and optical characteristics of these carotenoids are described. Evidence for the presence of minor carotenoids in the retina is cited. Studies of the dietary intake and serum levels of the xanthophylls are discussed. Increased macular carotenoid levels result from supplementation of humans with lutein and zeaxanthin. A functional role for the macular pigment in protection against light-induced retinal damage and age-related macular degeneration is discussed. Prospects for future research in the study of macular pigment require new initiatives that will probe more accurately into the localization of these carotenoids in the retina, identify possible transport proteins and mechanisms, and prove the veracity of the photoprotection hypothesis for the macular pigments.
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                Author and article information

                Journal
                Br J Nutr
                Br. J. Nutr
                BJN
                The British Journal of Nutrition
                Cambridge University Press (Cambridge, UK )
                0007-1145
                1475-2662
                14 January 2017
                : 117
                : 1
                : 108-123
                Affiliations
                [1 ]Macular Pigment Research Group, Nutrition Research Centre Ireland, School of Health Sciences, Waterford Institute of Technology , Waterford X91 K236, Republic of Ireland
                [2 ]Howard Foundation , Cambridge CB25 ONW, UK
                [3 ]Downing College, University of Cambridge , Cambridge CB2 1DQ, UK
                [4 ]Northern Ireland Centre for Food and Health (NICHE), University of Ulster , Coleraine BT52 1SA, UK
                Author notes
                [* ] Corresponding author: Dr D. Kelly, email davidkelly_24@ 123456yahoo.co.uk
                Author information
                http://orcid.org/0000-0001-6683-249X
                Article
                S0007114516003895 00389
                10.1017/S0007114516003895
                5297582
                28122649
                09704d4f-c7c9-49d6-baaf-4c625fc16d1a
                © The Authors 2017

                This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 05 July 2016
                : 30 September 2016
                : 11 October 2016
                Page count
                Figures: 4, Tables: 3, Pages: 16
                Categories
                Full Papers
                Human and Clinical Nutrition

                Nutrition & Dietetics
                lutein,zeaxanthin,meso-zeaxanthin,macular pigment,carotenoid-enriched eggs,serum carotenoids,cholesterol

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