Preserving Eyesight with Lutein & Zeaxanthin
By Mandy Magias
By far the most important sensory organs are our eyes, which we rely heavily upon to provide us with details of the world around us. Our eyesight allows us to enjoy the vast array of colours, shapes and patterns in our everyday lives, whilst providing us with visual cues to keep us alert and safe from danger. For something utilised day in and day out, eyesight is often taken for granted. Degenerative eye diseases are common and evidence shows that the projected number of pe ople with the disease is increasing exponentially . Without regular eye examinations these diseases can progressively develop from early to advanced stages, showing no symptoms until the irreversible onset of vision impairment. The key to avoiding diseases like age-related macular degeneration is prevention or at least slowing progression, which can be achieved through the potent actions of the two nutrients, lutein and zeaxanthin.
AGE-RELATED MACULAR DEGENERATION (AMD)
The macula is a small central layer of tissue in the retina which is responsible for our central visual field. It contains a high density of cone cells specialized to provide high acuity vision. It enables us to see clear and crisp images used frequently for activities such as reading, writing, driving and looking at detailed and coloured objects. But like any tissue, the macula can succumb to deterioration with age, accelerated by accumulation of harmful free radicals. The degeneration of the macula region leads to impaired central vision, which becomes foggy or blurred and can eventually result in blindness. As there is no cure for AMD, the main priority is to prevent and delay the progression of the disease.
Figure 1. Anatomy of the human eye. Lutein and zeaxanthin are xanthophyll carotenoids located in the upper layer of the macula of the retinal structure.
AMD RISK FACTORS
In a majority of cases, the development of AMD is most likely caused by the combination of factors that are linked to the deterioration of the macula and eye health, these include preventable and non-preventable risk factors depicted on this schematic.
Basic steps in preventing or delaying the progression of AMD are to cease smoking and wear polarized sunglasses to limit the damage of direct sunlight exposure to the eyes. Exercise and reducing saturated fats in the diet are the next step, to help maintain normal blood flow and reduce the accumulation of fatty plaque deposits in the macula. This can help in reducing the risk of hypertension and obesity as well. Age and genetics are non-preventable risk factors, but can be used to evaluate the total level of risk. A person over 50 years of age, with a family history of eye degenerative diseases should therefore take extra preventative measures. Aging increases the risk of oxidative damage, thus a diet rich in antioxidants, vitamins, minerals and carotenoids that accumulate in eye tissue are important.
Two of the most important nutrients for preserving the macula, are lutein and zeaxanthin. They are obtained from the diet and their main role within the body is to protect the macula.
LUTEIN & ZEAXANTHIN
Lutein and zeaxanthin are xanthophyll compounds, yellow pigments that are part of the carotenoid family. They are isomers, differing only by the position of one double bond in their structure and work together to protect the retina and enhance visual performance. Lutein and zeaxanthin are found in many plants, including green leafy vegetables and fruit. In plants, they absorb excess light energy to prevent damage caused by too much sunlight and harmful blue light (high-energy light rays).
Figure 2. The chemical structure of the three xanthophyll compounds, lutein, zeaxanthin and meso-zeaxanthin
In the human body, these carotenoids have a specific function, which is similar to their role in plants. Both molecules accumulate in high concentrations in the macula, giving it a yellowish colour. By absorbing UV and blue light from the sun, they prevent the harmful light energy reaching underlying light-sensing structures in the retina. This protects the eye from free radical photoreceptor damage that could lead to macular degeneration. Furthermore, lutein and zeaxanthin also accumulate in the iris, lens, ciliary body and other areas of the retina. They exhibit potent antioxidant properties within eye tissue and thus protect the eye from age-related degeneration. A third xanthophyll in the macula called meso-zeaxanthin has recently been discovered, but it is not found in any food sources and is believed to be synthesized in the retina from lutein.
Preclinical studies have shown lutein and zeaxanthin are effective at eliminating singlet oxygen particles and can prevent lipofuscin formation and cell death in highly oxidative conditions [2, 3]. Clinical reports suggest that lutein and zeaxanthin are important for reducing glare discomfort, recovery time from photo-stress and enhancing chromatic contrast and the visual range . These findings are consistent with previous reports that show increased macular pigment optical density (MPOD) leads to enhanced visual performance . The MPOD is also positively correlated with the speed of stimulus perception, and results of clinical studies revealed a significant increase in visual processing speed following lutein and zeaxanthin supplementation [6, 7], highlighting the benefits of these nutrients in young and healthy individuals.
Epidemiologic research demonstrates higher lutein and zeaxanthin eye tissue concentrations are associated with a significantly reduced risk of AMD (57%-82%) and nuclear cataracts (32-42%) [8-11]. It has also been observed that a daily dietary intake of lutein of 6mg and above is associated with a reduced risk of AMD and cataracts . A large case-controlled study highlighted that lutein and zeaxanthin levels were independently associated with reduced risk of AMD (35%), geographic atrophy (55%) and drusen (27%) . Numerous studies have found lutein and zeaxanthin supplementation significantly improve MPOD in both healthy individuals and AMD patients [13-20], indicating improvement in visual function with trends related to contrast sensitivity and visual acuity [14, 16]. A recent study assessed an additional measure of retinal function, known as multifocal electroretinography (mfERG), which measures the electrical activity generated by cells in the retina in response to a light stimulus. This longitudinal, randomized clinical trial demonstrated a trend for improvement in both retinal parameters, MPOD and mfERG in healthy eyes, following lutein-based supplementation . Lutein and zeaxanthin supplementation also results in increased visual acuity and reduced foveal thickness in patients with diabetic retinopathy . Additionally, lutein and zeaxanthin supplements have demonstrated their ability to improve vision and reduce cavitations in patients with macular telangiectasia type 2  and Alzheimer’s disease .
Other natural antioxidants like beta-carotene, vitamins C and E as well as nutrients important for eye health, such as omega-3 fatty acids, zinc and selenium are shown to be beneficial towards protecting the eyes from degenerative diseases particularly when combined together. The National Eye Institute’s Age-Related Eye Disease Study (AREDS) demonstrated a supplement combining beta-carotene, zinc and vitamins C and E could effectively reduce the risk of developing AMD by 32% and maintain visual acuity over 6 years [25, 26]. A second AREDS trial illustrated that lutein and zeaxanthin could be interchanged with beta-carotene without altering the effects of delaying disease progression . Another trial using the same combination (lutein, zeaxanthin, zinc and vitamins C and E) significantly improved visual acuity and slowed progression towards AMD .
The xanthophylls, lutein and zeaxanthin, are selectively found within the retina and are essential for the maintenance and protection of the macula. Low macular pigment levels of lutein and zeaxanthin are associated with a higher risk of AMD, as opposed to high dietary intake and high serum levels which are correlated with a lowered risk of disease. Lutein and zeaxanthin supplementation could be beneficial for those with a family history of AMD, those prone to oxidative damage due to lifestyle factors, and those who do not consume a diet high in carotenoid rich vegetables and fruits. In combination with other nutrients essential for eye health, supplementation may provide extensive benefits for delaying progression of AMD and preserving eyesight.
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