Carotenoids—Lutein and Zeaxanthin
In general, carotenoids are yellow, orange, or red pigments that are soluble in lipids. Mammals utilize carotenoids for a variety of functions but are incapable of synthesizing them. Thus, carotenoids must be obtained solely from the diet. Of the 600 carotenoids found in nature, only dietary lutein and zeaxanthin are deposited in the macula. Meso-zeaxanthin is a compound derived from lutein that is also present in the macula—it is converted by the body from lutein rather than being introduced from dietary sources.
The lutein and zeaxanthin present together in the macula are known as macular pigment.1 The macular pigment appears as a yellow tint in Figure 1. The intense deposition of the yellow-colored pigments in and around the fovea provided the basis for the clinical description of this area as the macula lutea or yellow spot. Lutein and zeaxanthin perform two primary functions in the macula. First, they filter high-energy, blue wavelengths of visible light as they enter the eye before they reach the photoreceptors.2 By passively absorbing these wavelengths, the macular pigment limits photo-oxidative damage to tissues that results from the reactive oxygen species (ROS) produced by these short wavelengths of light. Second, the macular pigment functions as an antioxidant to directly protect the retina from damage caused by ROS. The macular pigment also protects vulnerable photoreceptors from damage caused by sunlight, indoor lighting, and even light emitted from computer monitors. In other words, lutein and zeaxanthin act like internal sunglasses for the eyes. This protection not only helps to maintain healthy vision now but also helps to reduce the risk for certain eye conditions.
Lutein and zeaxanthin are found naturally together in vegetables such as spinach, kale, broccoli, corn, green peas, and green beans as well as other foods such as eggs.3,4 The bioavailability of lutein, unlike that ofmany other nutrients, is enhanced by chopping and cooking the food. This is likely due to the disruption of the strong interaction between chlorophyll and lutein molecules. It is difficult, however, to obtain beneficial amounts of lutein and zeaxanthin from diet alone. Interventional studies report that 10mg of lutein (specifically FloraGLO® brand lutein) per day is effective in improving vision and reducing the risk for certain eye conditions.5 FloraGLO Lutein provides the same lutein as is found naturally in vegetables and other foods but is obtained from marigold flowers through a patented process as shown in Figure 2.
The average daily intake of lutein and zeaxanthin in the US from diet alone is estimated to be less than 2mg,6 far below the 10mg per day clinically reported to reduce the risk for certain age-related eye conditions and improve visual function. How can we bridge the gap? As discussed earlier, increased consumption of foods with high concentrations of lutein such as dark green leafy vegetables, corn, and eggs can help increase lutein intake to 10mg per day. However, for many individuals changing dietary habits is not a practical option, which is why supplementing one’s diet with lutein-fortified foods/beverages or eye vitamins containing FloraGLO is an easy, alternative way to bridge the dietary lutein gap. In fact, the FloraGLO Lutein found in ocular supplements has been shown to be approximately twice as bioavailable as the lutein in green vegetables, again due to the strong interaction between lutein and chlorophyll in leaves.7,8
When recommending eye vitamins to patients, it is expected that the products will deliver the health benefits promised on the label. However, the ingredients in these products should have demonstrated bioavailability to deliver on claims made on product packaging. Certain ingredients, including lutein, are unstable in their purified forms and must be wrapped in a protective coating for inclusion in the eye vitamin. Data indicate that these different coatings may significantly affect the bioavailability of the lutein ingredient.9 Leading eye vitamin manufacturers choose FloraGLO as their lutein source because of its proven quality and safety profile, as well as its proven benefits for eye health. It is the most clinically researched lutein brand in the world and has over a dozen published studies demonstrating its absorption into the blood and increased lutein levels in the macula with daily supplementation at 10mg.
Macular Pigment Optical Density
The ability of the macular pigment to absorb or filter blue light is measured as macular pigment optical density (MPOD). MPOD is an optical indicator of the concentration of lutein and zeaxanthin in the macula and is becoming an accepted biomarker not only for predicting the risk for disease but also for visual function. In numerous studies, MPOD is linearly related to the levels of lutein in the serum and positively correlated with dietary intake of lutein and zeaxanthin. MPOD measurement is a relatively new technology, with only a few devices commercially available to evaluate MPOD; however, it has been well studied clinically. Over two dozen studies have been published demonstrating an increase in macular pigment following lutein and/or zeaxanthin supplementation at a range of 2–30mg per day or a high-carotenoid diet.10–24 The degree of increase in MPOD levels following lutein or zeaxanthin supplementation varies, likely due to subject demographics, disease state, measurement method, diet, and supplementation regimen.
Macular pigment, likely via its blue-light-filtering property, has been shown in a number of clinical trials to enhance visual performance—the ability to perceive detail and carry out visual tasks. High levels of macular pigment contribute to improved visual acuity, glare tolerance and recovery, contrast sensitivity, chromatic aberration, and photophobia in healthy individuals as well as those diagnosed with agerelated eye diseases.15,17,25–30 One study conducted in healthy volunteers demonstrated a 58% increase in glare tolerance and a five-second reduction in photostress recovery time following daily supplementation with 10mg FloraGLO Lutein and 2mg OPTISHARP® (DSM IP Assets B.V. Ltd) Zeaxanthin for six months. Improvements in these parameters of visual performance can have a major impact on everyday activities. Glare can present a significant hazard to drivers at night because of the bright light from oncoming headlights; the reported five-second reduction in recovery time can thus significantly improve night-time driving safety. Glare is also a challenge for athletes and outdoor enthusiasts who rely on their vision to help them perform at their best.
Macular Pigment and Age-related Eye Conditions
Lutein has been associated with risk reduction for age-related macular degeneration (AMD) for over a decade. This link originated from an epidemiologic study from the Eye Disease Case Control (EDCC) Study group published in 1993, and a follow-up study by Seddon and colleagues on a subset of ADCC patients published in 1994.31,32 The results indicated that the risk for developing AMD was 57% lower in individuals with the highest lutein and zeaxanthin intake compared with those with the lowest.31 These epidemiologic studies provide evidence that consumption of lutein and zeaxathin from food is associated with a reduced risk for AMD. The National Eye Institute is currently evaluating the progression of AMD following supplementation with FloraGLO Lutein and OPTISHARP Zeaxathin in a large population diagnosed with early AMD, the second Age-related eye disease study (AREDS2).
Nutritional intervention in the form of supplements was first evaluated by the National Eye Institute in AREDS. AREDS demonstrated that taking a supplement containing beta-carotene, vitamins C and E, and the minerals zinc and copper reduced the risk for progression to advanced AMD by 29% and reduced visual acuity loss by 21%.33 Lutein and zeaxanthin were not included in the AREDS study, in part because during the planning stages of the study in the early 1990s, lutein and zeaxanthin were not commercially available as ingredients. The in-progress follow-up study AREDS2 has added 10mg FloraGLO Lutein and 2mg OPTISHARP Zeaxanthin per day, alone or in combination with 1g of omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), to the original AREDS supplement formulation to assess their influence on progression to advanced AMD in individuals at high risk for the disease over the course of five years.34 In addition to evaluating the rate of AMD progression, other simultaneously evaluated outcomes include the effects of supplementation on cognitive function, cataract development, cardiovascular disease, vision loss, and visual function. A subset of subjects will also have their MPOD measured to provide further insight into the relationship between MPOD levels and AMD progression.
There is a growing body of evidence that, although not conclusive, supports that lower levels of MPOD may be a risk factor for certain age-related eye conditions. Increased MPOD may provide greater protection against oxidative damage, which contributes in part to the manifestation of AMD. For example, risk factors for AMD including tobacco use, light iris color, advanced age, obesity, and female gender are associated with low levels of MPOD.35 Significantly less macular pigment has been found in eyes at high risk for AMD because of advanced disease in the fellow eye compared with eyes with no known risk.36,37 In a study measuring MPOD in 93 AMD eyes and 220 normal eyes, the results showed that AMD patients who were not taking lutein supplements had 32% lower MPOD than healthy subjects. Interestingly, AMD patients taking high-dose lutein supplements after their initial AMD diagnosis were found to have MPOD levels indistinguishable from those of control patients, although the study did not evaluate the effects of supplementation and increased MPOD on the progression of the disease.38
In addition to being present in the macula, lutein is also deposited in the lens, albeit at much lower concentrations.39,40 The fact that oxidation of the lens is a major cause of cataracts suggests that antioxidant nutrients may play a role in cataract prevention. In support of this hypothesis, high lutein and zeaxanthin intake from dietary sources has been linked to the reduction in risk for cataract extraction in a number of epidemiologic studies.29,41–45
Nutritional intervention has also been shown to slow vision loss associated with retinitis pigmentosa. The National Eye Institute recommends that most adult patients with the common forms of retinitis pigmentosa take a supplement of 15,000IU of vitamin A daily under the supervision of their eye care professional. A study published in April 2010 suggests that the addition of 12mg per day of FloraGLO Lutein to this vitamin A regimen can slow the loss of midperipheral field sensitivity to a greater degree than vitamin A alone.22 In fact, the authors of this study conclude that “the benefit of lutein supplementation on the long-term course of midperipheral visual field loss among patients also taking vitamin A and eating an oily fish diet would be three to 10 years of protection against further loss of sight.”
Practical Application
MPOD has the potential to become a commonly tested biomarker to measure an individual’s risk for eye disease and to assess visual function. Knowledge of an individual’s MPOD level indicates whether he or she is getting enough lutein and zeaxanthin through their diet or supplementation regimen. Identification of individuals at low, medium, and high risk for eye disease can be made based on their MPOD level.46 MPOD is typically measured on a logarithmic scale and values range from undetectable to over 1.0 optical density units (du). Experts agree that a central MPOD below 0.2du is considered low, between 0.2 and 0.5du is mid-range, and levels above 0.5du are high.46 When compiling data from numerous studies across a diverse US population, nearly half of all Americans have low MPOD, indicating low concentrations of lutein and zeaxanthin in the macula.47 As low MPOD is a risk factor for AMD, nearly half of the American population—approximately 133 million individuals—may be at risk for developing AMD later in life. For individuals with low MPOD, lifestyle changes such as maintaining a healthy bodyweight, stopping the use of tobacco products, and eating more dark green, leafy vegetables may increase MPOD levels. For those who may find these lifestyle changes difficult, taking a daily eye vitamin with FloraGLO Lutein is a proven method to significantly increase MPOD, thereby improving visual performance and reducing risk for certain age-related eye conditions.
Conclusion
The scientific literature shows that lutein and zeaxanthin are essential nutrients needed by our eyes daily. Lutein and zeaxanthin cannot be synthesized by the body, so these nutrients must be consumed from dietary sources or supplements. High concentrations of lutein and zeaxanthin in the macula reduce the risk for certain eye conditions and are also associated with improvements in visual function. Science suggests that 10mg lutein and 2mg zeaxanthin per day can increase MPOD levels to those associated with eye health benefits. Not all lutein in supplements are equivalent and, with the ability to measure MPOD, the bioavailability of a particular lutein ingredient is more easily confirmed. Recommending an eye vitamin containing a proven, high-quality lutein ingredient, such as FloraGLO, is critical to ensure that patients are getting the optimal eye protection associated with higher levels of MPOD.
