Background
The carotenoids lutein and zeaxanthin are found in the retina of the eye and in particularly high concentration in the yellow spot, that structure in the center of the retina with the greatest density of photoreceptors that achieves the highest visual acuity. They are selectively enriched there and their concentration is much higher than in other tissues. They have also been found in the lens.
Structure and properties
Lutein and the functionally closely related isomer zeaxanthin are carotenoids of the xanthophyll group. They cannot be metabolized to vitamin A and differ from other carotenoids in having oxygen in the molecule. They have two free hydroxyl groups, which can be esterified with fatty acids as mono- or diesters. “Free” lutein refers to the unesterified lutein without fatty acid. Lutein and zeaxanthin form orange-yellow crystals, are odorless, lipophilic, and insoluble in water. C40H56O2, M = 568.8 g/mol.
Effects
Lutein and zeaxanthin are thought to have (photo)protective functions in the yellow spot of the retina of the eye. First, as antioxidants, they are thought to neutralize free radicals generated by incoming light. Second, they are thought to filter out a large proportion of the blue, high-energy and potentially harmful portion of visible light.
Mechanism of action
The conjugated double bonds mediate the light-absorbing effect. The absorption maximum is at approximately 445 nm for lutein and 450 nm for zeaxanthin. Visible light is in the range of 400-700 nm.
Origin
Although lutein and zeaxanthin are found in high concentrations in the yellow spot and appear to have physiological functions, they cannot be formed in the human or animal organism and are consumed exclusively in the diet primarily from plant sources. Both carotenoids are found in many fruits and vegetables. Particularly high concentrations are found in cabbage and spinach. Other sources include broccoli, Brussels sprouts, lettuce, leeks, beets, potatoes, cucumbers, zucchini, tomatoes, peas, squash, pepperoni, corn and oranges. Since chickens ingest them in their food, they are also found in egg yolks, to which they impart color. For commercial purposes, they are extracted from marigold flowers (Figure).
Indications
Lutein and zeaxanthin have not yet been approved as medicinal products in many countries and are not included in the Swissmedic substance list. They are not officially approved in the following indications and have been sold as food supplements to date. The scientific data situation is still insufficient and evidence for efficacy in these application areas is lacking.
- Macular degeneration: age-related macular degeneration is a degenerative disease of the yellow spot and the most common cause of blindness in the elderly in the Western world. Research to date suggests that an adequate supply of lutein and zeaxanthin may protect against the development of macular degeneration and may influence its progression in existing disease.
- Cataracts: use in the prevention or treatment of cataracts is also being discussed, as both carotenoids have also been found in the lens. Small studies in other eye diseases such as retinitis pigmentosa have been conducted.
Supplementation may be considered in the elderly, patients with degenerative eye disease and when dietary intake is inadequate.
Dosage
Adults: the usual daily dietary intake is about 1-3 mg. The most popular preparations on the market contain 5 to 10 mg of lutein and are taken once daily. Zeaxanthin is usually additionally contained in smaller amounts, because it also occurs in nature in smaller amounts than lutein. The dosage in most studies was 10 mg once daily. Most products on the market are not monopreparations, but contain additional minerals, vitamins and antioxidants that are considered important for the eyes.
Contraindications
- Not well enough known.
- Hypersensitivity
- Infants and children, pregnancy and lactation, special risk groups: No statement possible.
- Smokers should not take excessive amounts as a precaution (see adverse effects).
Interactions
Not sufficiently known.Both substances are very lipophilic. Absorption is favored by fats in the diet and lowered by certain dietary fibers.
Adverse effects
Based on the studies conducted to date, it can be assumed that the product is well tolerated. No adverse effects have been observed with regular intake of 10 to 30 mg of lutein over several months. However, since it has not yet been adequately studied, it should still not be used without caution. Hypercarotenemia and hyperpigmentation of the skin at high doses have been reported. Taking high doses of beta-carotene (≥ 20 mg) may increase the risk of lung cancer in smokers. Whether the same is true for lutein and zeaxanthin cannot yet be ruled out and should be considered.
Things to know
- Luteus: golden yellow, xanthós: sandy yellow, blond.
- In the retina is also found -zeaxanthin, which is apparently formed there by metabolizing zeaxanthin.
