Lutein, Zeaxanthin, beta-carotene and Astaxanthin
The bright pigments found in plants are attributable to the colorful compounds known as carotenoids. These compounds are highly absorbed into the retinal pigment epithelium, which is the layer just below the retina’s rods and cones. They provide antioxidant activity and help to build healthy macular pigment, which is measured as MPOD, or macular pigment optical density.
In the original AREDS research published in 2001, beta-carotene was used. Beta-carotene is a precursor form of vitamin A, and it was so strongly suspected of being an effective antioxidant, that it was given to smokers in studies designed to assess how much lower their rate of lung cancer would be. It had the opposite effect – it increased the rate of lung cancer in smokers. Therefore, smokers are advised to avoid high doses of beta-carotene.
Lutein is the most famous carotenoid. Lutein is most commonly derived from orange-colored marigold flowers, where it is in high concentration. Brand names of lutein include FloraGLO from Kemin and Lutemax 2020 from Omniactives. Lutein gravitates to the retina, but much lutein absorption of the retina is just off-center.
Zeaxanthin, on the other hand, which can be derived from paprika, marigold flowers or synthetic sources, concentrates in the very center of the retina, which is known as the foveola. It is therefore a vitally important molecule for eye health. Humans preferentially absorb and are able to use “dietary zeaxanthin,” which is the form found in nature. There is a transient molecule that is also found in the retina known as meso-zeaxanthin, but it is generally found in supplements and not in nature. The AREDS 2 research did not find any benefit to meso-zeaxanthin, and did not study that compound.
Astaxanthin is typically harvested from colored underwater plants. While it has antioxidant properties and is advertised as helping for eye fatigue, there are no reputable studies demonstrating clear efficacy for macular degeneration. It too was not included in AREDS 2.