Of the 20 observational studies assessed by this systematic review, 13 found that the carotenoids lutein and zeaxanthin might prevent or alleviate age-related macular degeneration.
The retina is the light-sensitive tissue at the back of the eye. The macula is the area of the retina with the highest concentration of photoreceptor cells, and thus a key factor in visual acuity.
Age-related macular degeneration (AMD) occurs when plaque deposits known as drusen start accumulating in the retina, though whether they cause AMD or are just a marker of the disease is unknown. As AMD progresses, the deposits expand and the macula becomes damaged, which can result in blurred vision (particularly in the center field of view), loss of color perception, difficulty seeing in low light, and in the end, blindness.
Lutein and zeaxanthin are carotenoids — a class of plant pigments — present notably in dark leafy greens. Once ingested, they appear to gather in the retina (lutein is dispersed throughout the retina; zeaxanthin concentrates in the macula). This finding in the late 1980s led to the hypothesis that these two carotenoids may benefit eye health. Since then, observational studies have noted an association between dietary intakes of lutein and zeaxanthin and a lower risk of AMD. Intervention trials, however, have produced mixed results. The systematic review summarized below assessed the available evidence.
This systematic review of 55 studies assessed the effect of dietary lutein, zeaxanthin, and meso-zeaxanthin (a metabolite of lutein and zeaxanthin) on AMD.
Of the 20 observational studies, 8 were prospective cohort studies (lasting 5–26 years) and 12 were either case-control or cross-sectional studies. They assessed either dietary intake (13 studies) or serum levels (7 studies) of lutein and zeaxanthin. The outcome most commonly assessed was the risk of AMD or of a subtype of AMD. The subtypes of AMD assessed were late AMD (neovascular AMD and geographic atrophy), intermediate AMD, and early AMD.
Of the 35 intervention trials (lasting between four weeks and five years), 27 assessed vision-related outcomes, 15 assessed serum levels of carotenoids, and 21 assessed macular pigment optical density (MPOD), a marker of retinal levels of lutein, zeaxanthin, and meso-zeaxanthin.
Of the 20 observational studies, 13 associated lutein and zeaxanthin with some benefit.
All 15 trials assessing the serum levels of lutein, zeaxanthin, and meso-zeaxanthin reported an increase following supplementation.
Of the 21 trials assessing MPOD, 19 reported an increase following supplementation with lutein, zeaxanthin, and meso-zeaxanthin.
Finally, here are the findings the 27 trials that assessed the effects of supplementation with lutein and zeaxanthin on vision-related outcomes:
Of the 18 trials assessing best corrected visual acuity, 6 found a benefit.
Of the 15 trials assessing contrast sensitivity, 10 found a benefit.
Of the 5 trials assessing photostress recovery time, 3 found a benefit.
Of the 5 trials assessing glare disability, 3 found a benefit.
Of the 4 trials assessing multifocal electroretinogram, all 4 found a benefit.
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