Zeaxanthin is an orange-yellow pigment that occurs naturally in plants and animals. In humans, zeaxanthin is found in the retina. It has antioxidant properties and is currently known to play a role in macular degeneration.
What is zeaxanthin?
Zeaxanthin is a pigment that appears orange-yellow and belongs to the group of xanthophylls. In turn, medicine classifies these among the carotenoids. In its pure form, zeaxanthin forms crystals that shine steel blue. Zeaxanthin exists in a solid aggregate state and melts at 215 °C. It is almost insoluble in water. It is almost insoluble in water, but is soluble in fat. The substance is also known as all-trans-β-carotene-3,3′-diol; this designation refers to the exact (bio)chemical properties of zeaxanthin. In addition, it can also be found under the label E161h as a food colorant. In the EU, the color is approved as an additive. The chemical compound occurs naturally in corn kernels, among other things, to which it gives its characteristic color. The molecular structure of zeaxanthin is composed exclusively of carbon, hydrogen and oxygen. Its molecular formula is C40H56O2.
Function, effects and tasks
Zeaxanthin forms a pigment in the lens of the eye and the retina. The retina contains the light-sensitive photoreceptors that convert optical stimuli into nerve impulses. In the center of the retina is the yellow spot (macula lutea). Together with another carotenoid, lutein, zeaxanthin gives the yellow spot its name. To a certain extent, the pigments prevent too much light from reaching the retina. Too much exposure could cause glare and possibly permanent blindness; zeaxanthin performs a protective function. Because the yellow pigment forms the complementary color to blue, zeaxanthin and lutein filter light with a wavelength that the human eye perceives as blue. This filtering primarily prevents oxidative processes from damaging the retina. Current research links this oxidation to macular degeneration, for example, which is associated with progressive deterioration of vision. In addition, zeaxanthin is found throughout the human body. While the yellow spot of the eye and the lens of the eye contain no other carotenoids besides zeaxanthin and lutein, the two substances, along with other carotenoids, are also found in the testes or ovaries, liver and adrenal glands. However, the effect of zeaxanthin in these organs is more nonspecific and contributes to the general balance.
Formation, occurrence, properties, and optimal levels
In foods, zeaxanthin is found mainly in corn kernels (Zea mays) goji berries and egg yolks. Other fruits and vegetables also contain zeaxanthin. The compound is found in the plastids of plant cells. A healthy and balanced diet can usually provide a person with enough zeaxanthin, so additional supplements or medical products are not necessary. Some medical studies recommend 6 mg of zeaxanthin intake daily; however, general guidelines do not exist, as they do for many other phytochemicals. This group of anutritive substances has no life-sustaining function, although it does have an impact on health. The zeaxanthin in medicines does not come from plants or animals, but from synthetic production. How much zeaxanthin the organism absorbs varies greatly between different individuals. The resorption rate also depends on other factors such as the availability of fats. After zeaxanthin has dissolved from other food components, it forms so-called mixed micelles with other substances. These are spheres into which different substances combine. The formation of the micelles increases the solubility of the individual substances. Passive diffusion transports the micelles into the cells of the duodenum and jejunum. The blood distributes the zeaxanthin together with other substances in the body.
Diseases and disorders
Age-related macular degeneration is considered to be the main cause of blindness in older age. It is particularly common after the age of 65. Signs include difficulty reading and seeing sharply, problems in contrast perception and color vision, and adaptation problems under changing light conditions.Affected individuals often perceive a gray haze around their field of vision and see only in a limited area. The cause of these complaints lies in the degeneration of the yellow spot. A complete cure for age-related macular degeneration is currently not possible. Some scientific studies showed a possible link between zeaxanthin and the disease. In these studies, subjects who consumed more zeaxanthin had a lower risk of developing age-related macular degeneration. These findings are controversial among researchers, however, because other studies have not found a reverse effect of low zeaxanthin intake: Subjects with low dietary zeaxanthin intake did not have a significantly higher risk of developing age-related macular degeneration. Nevertheless, there is clinical evidence that antioxidant intake can slow or mitigate macular degeneration. Physicians typically use a combination of therapies that include radiation, laser treatment and photodynamic therapy. Zeaxanthin is not only associated with age-related macular degeneration, but also with cataracts. This is another eye disease that causes opacities. Medicine refers to these opacities as cataracts. Studies showed that individuals with high zeaxanthin intake were less likely to develop cataracts that required intervention. However, it is not yet conclusively understood how this effect occurs. It is also possible that the observed effect is due not only to zeaxanthin (and lutein) but to a high concentration of carotenoids in the diet in general.
