Lutein belongs to the carotenoid group of substances and is known as the eye vitamin. It is produced exclusively in plants, where it functions as an important ingredient of chloroplasts. In the plant organism, it serves as an energy-collecting molecule to effectively utilize solar energy in photosynthesis.
What is lutein?
Lutein is a carotenoid and, along with zeaxanthin, is one of the xanthophylls. It contains 40 carbon atoms, 56 hydrogen atoms and two oxygen atoms. Between the carbon atoms there are 10 conjugated double bonds and one single double bond. A cyclohexanol ring containing three methyl groups is attached to each end of the carbon chain. Both rings also have hydroxyl groups. Therefore, the lutein molecule does not belong to the provitamin A molecules (beta-carotenes). Despite the hydroxyl groups, lutein is lipophilic. The conjugated double bonds determine the properties of lutein and the related xanthophylls. They produce the orange-yellow color, so that lutein is also traded as a food colorant under the designation E 161b. Conjugated double bonds are characterized by the alternation of single and double bonds. This allows the double bonds to interact with each other, resulting in better energy distribution and, above all, better energy absorption by the molecule. Thus, lutein absorbs light in the short-wave blue and ultraviolet spectrum, resulting in a better energy yield in plants during photosynthesis and a protective effect for the eyes in animals and humans. At the same time, the lutein molecules also absorb energy from highly excited singlet oxygen and thus have an antioxidant effect. Thus, they are able to scavenge free radicals (excited oxygen).
Function, effect, and tasks
These properties of lutein predestine it for protective effects especially in the eyes. It has been found that a high concentration of carotenoids in the retina significantly reduces the risk of developing macular degeneration (AMD). The macula is the yellow spot on the retina. It contains a particularly large amount of optic nerves and, for their protection, also a lot of lutein and zeaxanthin. With increasing age, however, degeneration of the macula occurs. There are two reasons for this. On the one hand, the cells are slowly destroyed by the influence of the short-wave and high-energy radiation of blue and ultraviolet light. On the other hand, the constant oxidative stress with the formation of free radicals also leads to the degradation of the retina. Therefore, the increasing age-related macular degeneration is a normal aging process, which, however, can be stopped by certain protective mechanisms. Lutein, together with its relative zeaxanthin, protects the eyes. Both xanthophylls absorb both short-wave blue light and neutralize highly excited aggressive oxygen at the same time. The action of the conjugated double bonds allows the absorbed energy to be well distributed within the molecule. The energy of the excited lutein and zeaxanthin is converted into heat energy and thus no longer has a harmful effect on the macula. Several studies have demonstrated the protective effect of lutein. The results were particularly clear in the case of already advanced AMD. Here, the slowing of the destructive processes could be best demonstrated. Lutein is always associated with zeaxanthin, which has a similar chemical structure.
Formation, occurrence, properties, and optimal values
As already mentioned, lutein is synthesized exclusively in plants, where it is a significant component of chloroplasts. It functions here as an energy collector, which contributes to the efficient utilization of solar energy. Unlike green chlorophyll, it is not degraded when light intensity is reduced. That is why the leaves turn yellow-orange in autumn. The animal and human organism is supplied with lutein exclusively through diet. Some organisms turn yellow due to accumulation of this substance in certain places. For example, the legs and claws of chickens have a yellow color only due to the enrichment of lutein. The yellow color of egg yolks is also produced by lutein. However, lutein, together with zeaxanthin, acquires special significance through its accumulation in the retina in the yellow spot, because this is where it exerts its most important protective effect against the macula. To protect the eyes, a diet rich in lutein is therefore useful.Particularly high amounts of lutein are contained in the green plant parts and leaves. The yellow color of flowers is also largely produced by lutein. Much lutein has among other things kale, parsley, spinach, broccoli, leaf lettuce, peas, Brussels sprouts or green beans. Absorption into the body occurs during fat digestion and takes place in the small intestine. Lutein is emulsified by bile acids and processed for absorption by the small intestine. Fats are necessary to promote lutein absorption, and saturated fatty acids are more suitable for this purpose than unsaturated ones. Humans depend on a steady intake of lutein because it cannot be synthesized in the human body. A continuous supply of lutein is a prerequisite for effective protection of the eyes against AMD.
Diseases and disorders
Acute adverse health effects from lutein are not known, because even the amount supplied through the diet would not be sufficient for this purpose. Carotenoids may increase the likelihood of cancer development. For example, years of research have suggested that constantly elevated levels of lutein increase the risk of lung cancer in women. However, there is insufficient statistical significance to make a definitive statement on this. Much greater health effects are caused by a deficiency of lutein. For the reasons mentioned above, lutein, along with zeaxanthin, plays an essential role in the visual process. Chronic deficiency of lutein therefore leads very quickly to complete blindness.
