INTRODUCTION
Carrots are involved in vision, thanks to their link to Vitamin A. Many of the yellow vegetables and fruit are yellow because of coloured chemicals called "carotenes". Once you eat these yellow vegies, your liver converts the carotenes to a family of chemicals that go under the name of Vitamin A.
If you don't have enough Vitamin A, you won't have healthy skin, a healthy immune system - and good vision. The Vitamin A travels in the blood to the retina (in the eye) where it is converted into a chemical called "retinal". When light hits this retinal chemical, it changes shape. This starts off a process, which ends with electricity travelling to the visual centres at the back of the brain - which turn the electricity into the wall-to-wall sensation that we call vision.
No Vitamin A means no retinal in your retina, which means no electrical signals travelling to your visual centres. So, if you don't get enough carotenes or Vitamin A in your diet, eventually you will suffer problems in your vision.
Carrots contain beta-carotene, which the body is able to convert into vitamin A, an essential vitamin for healthy vision. Vitamin A, also called retinol, is key in fighting vision problems like cataracts, glaucoma, macular degeneration and night blindness. It is found primarily in fish oils, liver, eggs and fortified dairy products. However, if you don't eat animal products, you can make sure you are getting plenty of vitamin A by eating fruits and vegetables that contain carotenoids like beta-carotene, which the body then converts to useful vitamin A, called "provitamin A."
Summary of β-carotene metabolism!
Mammalian Metabolism of β-Carotene: Gaps in Knowledge. 2013
Bright yellow or orange fruits like carrots, apricots and sweet potatoes are good sources of beta-carotene, while green leafy vegetables, especially broccoli, are rich in the carotenoids lutein and zeaxanthin.
Vision loss is one of the most feared health conditions, but sufficient vitamin A intake may help ease those fears. Vitamin A helps safeguard sight by protecting against free radical damage that can lead to vision problems like CATARACTS, MACULAR DEGENERATION and NIGHT BLINDNESS. While research has linked vitamin A deficiency to a variety of vision problems, one of the first signs that your eyes are not getting enough vitamin A may be episodes of night blindness. Vitamin A is especially important to the rods of the eye, which allow sight in dim light.
In the book Smart Medicine for Healthier Living, authors Janet Zand, Allan N. Spreen and James B. LaValle write, "The rods are cylindrical-shaped cells on the surface of the retina. They contain a special chemical called visual purple, or rhodopsin, that is responsible for vision in low-light conditions. Rhodopsin is formed from protein and retinol, a form of vitamin A ... if you lack sufficient vitamin A, the production of rhodopsin suffers, leading to increased difficulty seeing in dim light." (Therefore, if you are having unusual difficulty driving at night or finding your seat in a dark movie theater, you may want to consider adding some more vitamin A to your diet). The authors of this book go on to say that if vitamin A deficiency is severe enough, it could also lead to abnormally dry eyes and even the appearance of white foamy patches called Bitot's spots on the eye's surface.
Cataracts is another common vision concern, especially for elderly patients, that can be prevented with proper nutrition. According to The Folk Remedy Encyclopedia, cataracts strikes nearly everyone by the age of 75, but this is another problem that can be prevented by adding more vitamin A to the diet. Alan H. Pressman writes in "The GSH Phenomenon" that recent studies have shown that people with a higher dietary intake of mixed carotenes – the vitamin A precursors – along with higher intake of vitamins E and C have significantly lower rates of cataracts. Vitamin A is also particularly important to the elderly, who often don't get enough nutrient-rich foods, because the vitamin can combat weakened immune system function or dry skin problems in older patients.
The health benefits of vitamin A are plentiful, especially in terms of visual health, so if you notice you're having a difficult time seeing at night, you may want to add some yellow and orange veggies to your diet. If it is important to you to protect your vision – and to most of us it is – try safeguarding your sight by eating right. In other words, it's time you listen to your mother, and start eating those carrots.
Review of nutrient actions on age-related macular degeneration. 2003
EYE AND VISION
Eye disease such as age-related macular degeneration (AMD) and the risks associated with certain cancers can be reduced eating carrots. Recent research shows that fighting eye disease and cancer may begin with eating carrots. Apparently carrots have many health benefits for our bodies.
The orange color of carrots comes from beta carotene and carrots are jammed packed with beta carotene. When we eat carrots, the body converts beta carotene into vitamin A and Vitamin A is essential in maintaining good vision. More importantly, Vitamin A is used by the body in the production of rhodopsin. This is a purple pigment that is needed to see in dim light. Eating foods that are rich in Vitamin A causes the body to produce more rhodopsin which raises the effectiveness of the light sensitive area of the retina. This improves night vision. Lack of Vitamin A has been shown to lead to night blindness and overall poor vision health.
The eye is a major sensory organ that requires special care for a healthy and productive lifestyle. Upon ophthalmoscopic examination, the macula appears as a yellow spot on the retina. This yellow coloration is due to the presence of carotenoid pigments, such as lutein and zeaxanthin. An increase in the intake of these carotenoids may modify the overall risk of AMD via the protection of retinal tissues from photo-oxidative damage. In fact, the macular pigment contains lutein and zeaxanthin, which protects the photoreceptor cell layer from light damage by filtering blue.
Numerous studies have identified lutein and zeaxanthin to be essential components for eye health. Lutein and zeaxanthin are carotenoid pigments that impart yellow or orange color to various common foods such as carrots, pasta, corn, cantaloupe, orange/yellow peppers, fish, salmon and eggs. Their role in human health, in particular the health of the eye, is well established from epidemiological, clinical and interventional studies.
Carrots really do help you see in the dark; beta-carotene-rich foods help prevent a variety of eye ailments. 2006
AMD, age-related macular degeneration
Age-related macular degeneration (AMD) is one of the leading causes of progressive, bilateral blindness in elderly individuals. AMD can be classified as non-exudative (dry) or exudative (wet). The pathogenesis of dry AMD involves the presence of extracellular debris (drusen) over the retinal pigmented epithelium (RPE). Upon ophthalmoscopic examination, the drusen appear as yellowish lesions in the macula.
The progression of drusen characteristically involves an increase and confluence of more drusen in a single lesion. The diffusion and growth of drusen determine the detachment of RPE with a loss of photoreceptors in the central macula and subsequent blindness. Dysfunction of the RPE, Bruch’s membrane, and the choroid are the principal mechanisms involved in the pathogenesis of AMD. Environmental and genetic factors influence the events underlying the disease and modify the individual risk factors of developing AMD. Due to the interaction between genetic and environmental factors, the etiology of AMD is multifactorial. As with other complex diseases, recent genome-wide studies have established and confirmed many genetic variants associated with a higher risk for AMD.
AMD, age-related macular degeneration!
Development of AMD disease. AMD is mainly due to photochemical damage and oxidative stress. In the figure it is represented by the cellular assessment of the normal macula (left side), the dry AMD (center), and the wet AMD (right side). In the left side of the image, the cells in the macula are normally represented. In the dry form of AMD (center), the drusen (composed of a core of glycolipids and glycoconjugates) impairs the metabolic connection between the choroid and the upper layers of macula, leading to degeneration of RPE and photoreceptors. In the wet form of AMD (right side), the production of neovascular factors determines the formation of choroidal neovascularization (CNV) with subsequent fluid leakage and major degeneration of RPE and photoreceptors. In the normal ageing process, the lipids accumulate in the Bruch’s membrane, causing a thickening of the membrane and improving the oxidative distress. Moreover, the Bruch’s membrane is lacking of an adequate intrinsic antioxidant system. Furthermore, the lipids can bind the macrophages inducing the secretion of the vascular endothelial growth factor (VEGF). The production of inflammation factors improves the damage to the RPE and photoreceptors and induces the formation of functional microvascular networks (choroidal neovacularization). Antioxidant factors might prevent the disease and delay its progression. In the upper portion of the image, the pool of nutrients involved in the onset (left side) and progression (right side) of the AMD are listed.
Role of LUTEIN and ZEAXANTHIN in human eyes
Lutein and zeaxanthin were found to be concentrated in the macula, a small area of the retina responsible for central vision. The hypothesis for the natural concentration is that they help keep the eyes safe from oxidative stress and the high-energy photons of blue light. Various research studies have shown that a direct relationship exists between their intake and pigmentation in the eye.
Macular degeneration
Several studies show that an increase in macula pigmentation decreases the risk for eye diseases such as age-related macular degeneration (AMD). The only randomized clinical trial to demonstrate a benefit for lutein in macular degeneration was a small study, in which the authors concluded that visual function is improved with lutein alone or lutein together with other nutrients and also that more study was needed.
There is epidemiological evidence of a relationship between low plasma concentrations of lutein and zeaxanthin, and an increased risk of developing age-related macular degeneration (AMD). Some studies support the view that supplemental lutein and/or zeaxanthin help protect against AMD.
In 2007, in a six-year study, John Paul SanGiovanni of the National Eye Institute, Maryland found that lutein and zeaxanthin protect against blindness (macular degeneration), affecting 1.2 million Americans, mostly after age 65. Lutein and zeaxanthin reduce the risk of AMD.
Cataracts
There is also epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataract development. Consumption of more than 2.4 mg of lutein/zeaxanthin daily from foods and supplements was significantly correlated with reduced incidence of nuclear lens opacities, as revealed from data collected during a 13- to 15-year period in the Nutrition and Vision Project (NVP).
Photophobia (abnormal human optical light sensitivity)
A study by Stringham and Hammond, published in the January/February 2010 issue of Journal of Food Science, discusses the improvement in visual performance and decrease in light sensitivity (glare) in subjects taking 10 mg lutein and 2 mg zeaxanthin per day.
age-related macular degenaration (AMD).
LUTEIN AND ZEAXANTHIN
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. They have also been linked with reduced risk of age-related macular degeneration (AMD) and cataracts. Research over the past decade has focused on the development of carotenoid-rich foods to boost their intake especially in the elderly population.
They have demonstrated several beneficial health effects due to their ability to act as scavengers for reactive oxygen species and to bind with physiological proteins in humans.
In general, carotenoids are tetra-terpenoid having 40 carbon skeleton made up of 8 isoprene units and comprise of two classes, namely carotenes (purely unsaturated hydrocarbons) and carotenoids with oxygen atoms which are referred to as oxygenated carotenoids or xanthophyll carotenoids. The macular carotenoids are dietary lutein and zeaxanthin, and their conversion isomer meso-zeaxanthin, which are non-provitamin A carotenoids, (i.e., it cannot be converted into vitamin A). Important members of oxygenated carotenoids are lutein, zeaxanthin.
The figure lists the chemical structure of the macular pigments found in the retina. Lutein and zeaxanthin are the main dietary carotenoids found in human retina and they protect the macula from damage by blue light, improve visual acuity and scavenge harmful reactive oxygen. Lutein and zeaxanthin along with their common metabolite meso-zeaxanthin, commonly referred to as macular pigments (MP). The ratio between lutein, zeaxanthin and meso-zeaxanthin changes as the eccentricity moves away from fovea. Although lutein and zeaxanthin were also detected in prenatal eyes, they did not form visible yellow spot. No age-related (between the ages of 3 and 95 years) differences were observed in the quantity of lutein and zeaxanthin. But, the ratio of lutein to zeaxanthin differed between infants and adults. In infants, lutein predominates over zeaxanthin in fovea, and the opposite is true after 3 years of age.
Structurally the difference between lutein and zeaxanthin is in the type of ionone ring, lutein contains a β-ionone ring and a ε-ionone ring, whereas zeaxanthin has two β-ionone rings. Lutein and zeaxanthin are isomers, but not stereoisomers, which differ in the location of a double bond unsaturation in the end ring. Lutein can exist in possible eight stereoisomeric forms because of three chiral centers, but in nature it exists mainly in Z (cis)-form (R,R,R). Zeaxanthin, on the other hand, has two chiral centers but, because of symmetry exists only in 3-stereoisomeric forms.
LUTEIN AND ZEAXANTHIN!
Evidences show that lutein and zeaxanthin are important dietary carotenoids in preventing and reducing cataracts and AMD.
A multi-center eye disease case-control study involving five ophthalmology centers in the US showed that a higher dietary intake of carotenoids, specifically lutein and zeaxanthin is associated with reduced AMD risk.
In general, the ageing processes cause biochemical, physiological and physical changes that are directly or indirectly responsible for the onset of many diseases including cataract and AMD.
However, over the years research has identified major contributing factors for both diseases.
Ageing (greater than 50 years of age) seems to be the major cause in both cases. In addition, other factors include exposure to ultraviolet light and blue light, oxidative stress due to access of oxygen radical species, environmental factors, and high polyunsaturated fatty acids responsible for AMD. High incidences of cataract have been linked to poverty and poor nutrition, and strict vegetarian diets lacking in antioxidants.
Recent studies also reported the prevalence of major eye diseases and showed that high plasma concentrations of lutein and zeaxanthin reduced the risk of age-related cataract in the elderly Finnish population by about 41% [85,86].
Lutein.
CONCLUSIONS
Increasing age is the dominating factor for the onset of cataracts and AMD because of physiological and biochemical changes due to old age. Global researchers have identified lack of lutein and zeaxanthin as dietary causes in cataract and AMD related blindness. To date large scale prevalence studies provide serious data that conclude ethnicity may be the other major factors. But, age, diet and ethnicity are not the only factors for cataract and AMD. Hence prevention programs should not be solely based on these factors. Other factors such as living (geographic location) and working environment, socio-economic standing and hitherto unidentified factors should also be investigated. More research looking into the development of high-xanthophyll functional foods is essential in order to develop dietary strategies for the management of cataract and AMD in particular for elderly people.
DAMILANO GIOVANNI
DELL'ACQUA ALESSANDRO
