Good diet and nutrition play important role in human health and to the eye. Good vision is provided by healthy eyes and which is essential for good and enjoyable life. Eye health related issues are growing globally. The globally major visual impairments are uncorrected refractive error, cataracts, glaucoma, age-related muscular degeneration, diabetic retinopathy.
Carotenoids are red, yellow and orange organic pigments that are produces by plants. They are also known as tetraterpenoids. Major carotenoids are alpha-carotene, beta-carotene, lutein, zeaxanthin, cryptoxanthin and lycopene.
Lutein and Zeaxanthin
Lutein and zeaxanthin are oxygenated carotenoids that consist of 40-carbon compounds with nine conjugated double bonds in the polyene chain. Lutein and zeaxanthin are classified together in nature as xanthophylls. Xanthophyll carotenoids copious in egg yolk and dark green leafy vegetables, possessing two hydroxyl groups. While these carotenoids are similar in structure to α- and β- carotene.
The structures of lutein and zeaxanthin characterized by the existence of two hydroxyl groups at the terminal rings of the molecule on the basic C40H56 carotene structure, and thus are referred to as xanthophylls. Zeaxanthin is a stereoisomer of lutein, differing only in the location of one double bond in one of the hydroxyl groups. The hydroxyl groups are believed to provide unique biological function of these two xanthophylls. Relative to hydrocarbon carotenoids, lutein and zeaxanthin are more hydrophilic and polar in blood and tissues. The hydrophilic properties allow them to react with singlet oxygen generated in water phase more efficiently than nonpolar carotenoids.20 Additionally, the relatively higher polarity partly determines distinctive characteristics during their metabolism, light absorption, capture and stabilization in tissues, and potential orientations in a bilayer membrane.
The absorption of carotenoid released from food include several steps
Distribution in the gastric emulsion to be combined into lipid droplets, followed by transfer to mixed micelles involving bile salts, biliary phospholipids,
dietary lipids and others.
- Solubilized carotenoids are then absorbed by the intestinal cell for transportation into blood system.
- These steps may include simple diffusion, uptake by micelles and receptor mediated and another transporter,
- The highest concentration of carotenoids in micelles (e., solubilization), corresponds to greater absorption and transportation into plasma.
over-all, bioavailability of carotenoids is affected by a number of factors including food matrix, processing conditions and fat content while the rate of bio-accessibility of carotenoids is greatly impacted by food matrix and processing.
Lutein and zeaxanthin benefits to human eyes
They constitute the main pigments found in the yellow spot of the human retina which protect the macula from damage by blue light, improve visual acuity and scavenge harmful reactive oxygen species (ROS). They have also been linked with reduced risk of age-related macular degeneration (AMD) and cataracts.
Age-related muscular degeneration
Age-related macular degeneration (AMD) is an eye disease that can blur the sharp, central vision that need for activities like reading and driving. “Age-related” means that it often happens in older people. “Macular” means it affects a part of your eye called the macula. AMD is a common condition — it’s a leading cause of vision loss for people age 50 and older. AMD doesn’t cause complete blindness, but losing your central vision can make it harder to see faces, drive, or do close-up work like cooking or fixing things around the house.
Several studies have shown that incidences of AMD can be reduced by consuming diets with high levels of lutein and zeaxanthin and supplementation by increasing their concentration in serum and parallel increase in macular pigment optical density (MPOD). For example, lutein supplementation over a 140-day period increased serum lutein level. Similarly, consuming increased spinach and kale in diet for a 4-week period increased the MPOD by 4%–5%. Recently, a systematic review and meta-analysis of several longitudinal studies have concluded that lutein and zeaxanthin affect positively.
Cataract is an condition of opacification of the lens in the eye which obstructs the passage of light, often resulting in impaired vision or blindness.
- A subcapsular cataract occurs at the back of the lens
- A nuclear cataract forms deep in the central zone (nucleus) of the lens. Nuclear cataracts usually are associated with aging.
- A cortical cataract is characterized by white, wedge-like opacities that start in the periphery of the lens and work their way to the canter in a spoke-like fashion. This type of cataract occurs in the lens cortex, which is the part of the lens that surrounds the central nucleus.
Antioxidant nutrients neutralize free radicals (unstable molecules) that are related with oxidative stress and retinal damage. This is why the antioxidants lutein and zeaxanthin likely play a role in preventing cataracts. In fact, a recent study demonstrated that higher dietary intake of lutein and zeaxanthin and vitamin E was linked with a significantly decreased risk of cataract formation.
Light induces retinal damage:
Light induced retinal damage depends largely on wave length, exposure time and power level. The characteristic of the muscular pigment that allows it to filter the incoming blue light orientation (back of the retina) and absorption spectrum (440 -460nm). Most of us know to protect our eyes against the sun, but high-energy blue light from digital screens bombards our eyes and may lead to eye strain and fatigue and eventually vision loss.
Lutein and its close relative zeaxanthin are found macula, the central portion of the retina that is responsible for sharp and detailed vision. Scientist believe these carotenoids may protect the macula by filtering harmful blue light and by antioxidant activity.
Dietary sources of lutein and zeaxanthin
Epidemiological studies suggest that increase intake of lutein lowers the risk for age-related muscular degeneration. Unfortunately, the human body does not naturally make the lutein and zeaxanthin it needs. This is why eating green vegetables is important. Getting daily amounts of lutein and zeaxanthin through your diet or nutritional supplements can help maintain good eye health. Like many other naturally occurring nutrients, the way the vegetables are prepared/consumed and the items that they are consumed with can affect how well the body can absorb them. As such sometimes additional supplements may be needed for optimal therapy.
Foods contain lutein and zeaxanthin
Lutein and zeaxanthin are the most common xanthophylls in green leafy vegetables (e.g., kale, spinach, broccoli, peas and lettuce) and egg yolks. They are also found at relatively high levels in einkorn, Khorasan and durum wheat and corn and their food products. The ratio of lutein and zeaxanthin in green vegetables has been reported to range between 12 to 63, highest being in kale, while in yellow-orange fruits and vegetable this ratio ranges between 0.1 and 1.4. They also quantified small amounts of lutein and zeaxanthin in breads prepared from modern wheat varieties.
The top 10 vegetables that contain Lutein and Zeaxanthin
- Turnip greens
- Dandelion greens
- Mustard greens
- Green peas
- Romaine Lettuce
- Summer squash
- Beet greens
Below are the top 20 foods that contain Lutein and Zeaxanthin