- Nutrients 2021, 13(12), 4409; https://doi.org/10.3390/nu13124409
- Published: 9 December 2021
by Xiang Li 1,Roberta R. Holt 1,Carl L. Keen 1,2,Lawrence S. Morse 3,Glenn Yiu 3 andRobert M. Hackman 1,*
1 Department of Nutrition, UC Davis, Davis, CA 95616, USA
2 Department of Internal Medicine, UC Davis, Sacramento, CA 95817, USA
3 Department of Ophthalmology and Vision Science, UC Davis Medical Center, Sacramento, CA 95817, USA
*Author to whom correspondence should be addressed.
Academic Editors: Maria Dolores del Castillo and LaVerne L. Brown
Abstract
Age-related macular degeneration (AMD) is the third leading cause of blindness worldwide. Macular pigment optical density (MPOD), a biomarker for AMD, is a non-invasive measure to assess risk. The macula xanthophyll pigments lutein (L) and zeaxanthin (Z) protect against blue light and provide oxidant defense, which can be indexed by MPOD. This study examined the effects of Z-rich goji berry intake on MPOD and skin carotenoids in healthy individuals. A randomized, unmasked, parallel-arm study was conducted with 27 participants, aged 45–65, who consumed either 28 g of goji berries or a supplement containing 6 mg L and 4 mg Z (LZ), five times weekly for 90 days. After 90 days, MPOD was significantly increased in the goji berry group at 0.25 and 1.75 retinal eccentricities (p = 0.029 and p = 0.044, respectively), while no changes were noted in the LZ group. Skin carotenoids were significantly increased in the goji berry group at day 45 (p = 0.025) and day 90 (p = 0.006), but not in the LZ group. Regular intake of goji berries in a healthy middle-aged population increases MPOD may help prevent or delay the development of AMD.
Keywords: goji berry; zeaxanthin; lutein; carotenoids; age-related macular degeneration; macular pigment optical density
1. Introduction
Age-related macular degeneration (AMD) is the leading cause of blindness among seniors in developed countries, and third worldwide after uncorrected refractive errors and cataracts [1,2]. In early stages, the disease is characterized by small to intermediate drusen with pigmentary changes that may progress rapidly to more advanced forms such as choroidal neovascularization or central geographic atrophy with loss of central vision [3]. Lutein (L), zeaxanthin (Z), and the isomer meso-zeaxanthin (meso-Z) are macular pigments that filter damaging blue light and provide oxidative defense in the macula. These pigments are found in plants as xanthophylls, with increased dietary intake proposed to reduce the development and progression of AMD [4]. The relative concentration of xanthophyll carotenoids in the retina can be measured non-invasively by psychophysical and objective methods, expressed as macular pigment optical density (MPOD) [5]. Numerous epidemiological studies report that individuals with a low MPOD level are at an increased risk of AMD [6].
Dietary L and Z are found in certain fruits and vegetables with red, yellow, or orange color, egg yolk, and in some green leafy vegetables [7,8]. The dietary intake of Z is lower than L in all age groups and ethnicities in the U.S. [9]. Dietary intakes of L and Z are strongly associated with their serum levels, as well as with MPOD [10]. Previous studies have shown that high intakes of these carotenoids from dietary sources or supplements can increase plasma L and Z, and MPOD [11]. Once early AMD has progressed to the intermediate stage, dietary supplements are indicated, but no clinical evidence yet exists for interventions that can address the prevention of small-intermediate drusen with pigmentary changes, the initial clinical signs of macular disruption [12].
Goji berry (Lycium barbarum L. and L. chinense), also termed wolfberry or Go Chi Zi, has been used in traditional Chinese medicine for more than 2000 years [13]. The bright red berry contains the highest amount of Z among all known dietary sources and is mainly present in a dipalmitate form [14,15]. The intake of zeaxanthin dipalmitate (ZD) extracts from goji berry increases plasma Z to a greater extent than non-esterified Z supplementation [16]. The berries also contain unique carbohydrates that are present as conjugates with peptides or proteins, which are often referred to L. barbarum polysaccharides (LBP). These have shown anti-inflammatory and neuroprotective effects in animal and cell culture studies [17].
The typical adult human eye has approximately 2.4 times more Z than L in the central fovea of the macula [18], making goji berry intake a prime candidate for increasing MPOD. Nevertheless, there is a paucity of clinical evidence on goji berry and MPOD particularly for the prevention or delay of progression from early to intermediate AMD. In individuals from China with signs of early AMD, 25 g of daily consumption of goji berries for 90 days significantly increased both serum Z and MPOD [19]. However, this study had a broad age range (51 to 92 years of age), some participants smoked, and others had certain pre-existing medical conditions. Additionally, the authors only reported central MPOD values up to 0.5 retinal eccentricity (RE), whereas macular pathology and visual dysfunction in AMD may extend beyond that central region. Therefore, to provide a more complete understanding of the influence of goji berry intake on the progression AMD, data is needed on for different population groups that measures MPOD at eccentricities over the entirety of the macula.
In the current study, we prospectively evaluated if the daily intake of 28 g of goji berries or a commercially available supplement providing 6 mg of L and 4 mg for 90 days can improve MPOD and skin carotenoid levels, an index of total carotenoid intake, among healthy middle-aged adults, 45 to 65 years old, with no signs of drusen or early AMD.
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