The Physiological Role of Lutein in Vision and Disease

LIM JU BOO 

BSc Post Grad Dip Nutr MSc MD PhD FRSPH

Fellow

Royal Society of Medicine

London

Chemistry of Vision:

Rhodopsin or visual purple is a sensory protein-containing pigment found in the rod cells of the retina requiring retinol or vitamin A for its synthesis.

In the event of vitamin A or carotene  deficiency (carotene is a precursor of retinol or vitamin A), the synthesis of rhodopsin is compromised, resulting in night blindness, and in severe cases lead on to xeropthalmia and keratomalacia and total blindness.

Hence the importance of an adequate intake of vitamin A or fruits and vegetables containing carotene which can be converted into retinol (vitamin A) by the body

However, retinol is not the only nutrient that ensures good vision in the dark in particular.

Lutein and Carotenoids:

There are other carotenoids that are also involved in good vision in both in the day and at night , one of which is lutein, the other zeaxanthin.

Lutein is a one of the carotenoids that acts as an antioxidant responsible for protecting the eyes. This phytochemical is found abundantly in most brightly colored fruits and leafy vegetables and in plant-based foods that have deep orange or yellow colours.

Many colorful fruits and vegetables such as kale, spinach, broccoli, water cress, kangkong, sayur manis, including mangoes, water melons, citrus fruits, in fact in most tropical fruits, and even egg yolk are rich not just in carotenes, the precursor of retinol, but are also abundant  in lutein and zeaxanthin.

Green tea too contains lutein and zeaxanthin in good amounts besides the catechins, a subgroup of the flavonoids, as well as  vitamins C and E,


So does a Chinese herb called Gou Qi Zi (Wolfberries) which has very high levels of zeaxanthin, lutein, polysaccharides and polyphenols, all of them  have been shown to improve eyesight, prevent macular degeneration and diabetic retinopathy.

Their rich presence in most colorful fruits, vegetables, teas, berries and herbs protects the eyes from oxidative stress and vision loss.

Like retinol, lutein and zeaxanthin cannot be synthesized by the human body and hence they must be obtained by the consumption of plant-based foods rich in these sources. However, lutein may also be  giving by lutein supplements.

Although it is best to source lutein naturally through foods rich in them,  other antioxidants supplements or fortified foods may also be used to help increase levels of lutein, zeaxanthin and carotene levels in order to confer the full potential of lutein in terms of disease prevention, bioavailability, metabolism and dose-response relationships

When foods rich in lutein or lutein supplement is consumed, scientists and nutritionists believe this is easily transported throughout the body, especially to the parts of the eyes called the macula and the lens where it is wanted most. Nutritional and food scientists know that there are more than 600 different types of carotenoids found in nature, but only less than two dozen find their way into the eyes.

Of these, approximately 20, lutein and zeaxanthin are the only two left that are deposited in high quantities into the macular portion of the eyes.  The macula is the central area of the retina which is the light sensitive, and it is in this area that lines the inner portion  of the eye that  gives us the ability to see an optimal “20/20”vision  and visualize the full range of colours.

Oxidative Radical Damage:

Furthermore, the antioxidant properties of lutein to block off free radical damage caused by blue light from smart phones or from other sources have been reported in the journal Nature.

A diet lacking lutein and other carotenoids may increase the risk of developing age-related vision loss or disorders related to macular degeneration and cataracts formation

Nutritionists and medical researchers are aware that lutein protects healthy cells like rods and cones in the eyes and skin cells, and its ability to arrest the growth of malignant cells.

One of the most important parts of the eye is the lens. The function of the lens is to collect and focus light onto the retina. This is exactly why the lens has to remain clear and transparent for light to enter. It has to be free from the cloudiness which is indicative of the formation of cataracts.

Energy of Light:

The main reason why the lens becomes cloudy is due to oxidation of the lipids in the lens by ultraviolet light and blue light which are shortwave ends of the light in the electromagnetic spectrum.

The shorter the wave length or the higher the frequency, the greater the penetrating and destructive powers of the electromagnetic spectrum including light as given in the Max Planck equation:

E = hv

where,  E = energy delivered, h = Max Planck constant, and v = the frequency

Thus blue light and ultra violet of the Sun can energize molecules in the eyes, the skin  and other tissues liberating highly destructive free radicals to the cells, especially the DNA, initiation molecular lesions on the sites where the light or radiation is turned on.

However the presence of antioxidants like lutein and zeaxanthin is able to block off these highly distractive free radicals that may ultimately lead to vision impairment, both to the lens and to the retina.

Even for those who may, or may not have existing eye and vision problem other than short or long sightedness, including plenty of lutein in their diet or in supplements can prevent  vision impairmemt Thus it is important to ensure we have adequate lutein intake.

Preventative measures are the best ways to ensure that our vision and eyes remain  intact and healthy even till old age. It is thus strongly advised that both the young and the old should ensure adequate consumption of foods rich in lutein, or the use of supplements so as to minimize the risk of oxidative damage to the eyes.

Cancers and Heart Disease:

Even though lutein, zexanthin and other carotenoids are extremely crucial for vision and the eyes, their benefits is also extended to other areas of the body.


For instance, lutein is also used in the prevention of skin disorders, several types of cancer including colon or breast cancer, type 2 diabetes as well as minimizing risk factors associated with coronary heart disease.

Macular Degeneration:

Lutein may be considered a natural treatment for macular degeneration (AMD), which is probably the most common cause of blindness among older adults in countries where vitamin A intake is adequate but where lutein is deficient.  

Estimates show that more than 25 million people worldwide are affected by age-related macular degeneration or cataracts, especially people aged 55 and older living in areas where exposures to ultra violet rays of the sun is highest such as in snow covered mountains of Tibet or in the tropical sun like in Malaysia.

For instance, the incidence of AMD in the United States is predicted to triple by 2025 according to the American Optometric Association

Mechanism of Action:

Lutein protects the eyes by blocking off a portion of the short-wavelength UV light or blue light that have the most damaging effects on the most delicate parts of the eyes such as the retina and the macula.


Researchers at Harvard University have found that supplementing with 6 milligrams daily of lutein can lower the risk for macular degeneration by an average of 43 percent.

Cataract & other Studies:

Similarly, other studies have demonstrated that a higher dietary intake of lutein and zeaxanthin along with vitamin E is associated with a significantly decreased risk of cataract formation. While the research is still in its early stages, it is suggested that taking lutein three times weekly for up to two years may confer an improvement in vision in older people who already have cataracts or at risk.

Other benefits of lutein intake or its supplements include a reduction in  eye fatigue, glare and light sensitivity especially those who plays with their smart phones constantly especially in the dark. It assists the lens and retina to remain intact while strengthening the eye tissues.

Individual Variations:

However, the requirements of lutein like for all other nutrients differ from individual to individual.  No one person is biologically the same. It’s likely that even for those with a relatively high intake of antioxidant-rich foods, their blood levels might be correspondingly high in the various nutrients, and yet their levels in the tissues within their eyes and at retinal levels may still be too low.

Scientists have now devised ways of measuring macular pigment levels of lutein in the eyes to determine the risk for retinal disease. By determining the macular pigment optical density test (MPOD), nutritionists and specialist doctors can now formulate more precise dietary recommendations for lutein and other protective nutrient requirements based on individual responses, genetic predisposition and lifestyle requirements

Skin Cancers:

It was shown that carotenoids including lutein and zeaxanthin are not just present in the eyes, but also in the skin. It is postulated that lutein may be able to filter out high-energy wavelengths of visible light such as blue light and ultraviolet radiation by slowing down the rate of free radical damage and oxidative stress. A few animal studies have shown that lutein provide significant protection against light-induced skin damage, such as signs of aging, the loss of skin elasticity, and potentially skin cancer.

Lowers risk of diabetes:

It was also demonstrated in some animal studies that high levels of lutein and other carotenoids within the blood are associated with a better control of blood sugar. This may be translated to a lower risk of diabetes and its complications.


For instance, a 2000 study conducted on diabetic rats found that oral supplementation with lutein and omega-3 fatty acid or DHA was able to normalize all diabetes-induced biochemical lesions in the experimental group.

Compared to the control of rats not given lutein and DHA, diabetic rats taking the supplements showed   lower oxidative stress rates and less damage to the retina of the eyes, even though they were under hyperglycemic conditions.

Lowers Risk of Cancer:

There was some evidence that people who obtain more lutein in their diet have lower rates of breast, colon, cervical and lung cancers. However, we do not know exactly how lutein and cancer formation is linked currently, even though correlational studies have shown that adults with higher levels of lutein in the blood experience a reduction of developing several forms of common cancers.

Thus it may be possible lutein could offer as a part of a natural cancer treatment because of the fact that foods rich in lutein such as broccoli,  kale, spinach,  leafy green vegetables and all highly colored fruits  with high antioxidants scores  can  lower inflammatory diseases due to oxidative stress.

But more research is still needed to help us fully understand the role lutein and other carotenoids have on cancer, immune response, hormonal and cardiovascular functions, independent of other nutrients and phytochemicals that are found in fruits and vegetables.


One possibility is their epigenetic influence on how genes express themselves in the presence of lutein and carotenoid-rich foods.

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Cardiovascular Protection:

A few  observational studies have demonstrated  that xanthophyll carotenoids including lutein can reduce the risk of cardiovascular events and  coronary heart disease and stroke However as in previous studies that show potential cancer-protective effects of lutein, we are not quite  sure as yet at this moment in time how lutein could be cardiovascular protective?  

One such possibility is lutein anti-inflammatory and antioxidant properties may inhibit inflammatory response which currently scientists and cardiologists believe is the primary cause of heart and vascular diseases.  This hypothesis is currently replacing the out-of-fashion high cholesterol theory.

Studies conducted at the University of Southern California suggest that low levels of lutein within the blood might contribute to the thickening of artery walls. This elevates the risk for arteriosclerosis development and clogging of the carotid arteries that can result in cerebrovascular accident or stroke.

The USC’s observational studies show that populations with the highest levels of lutein in the blood experience less plaque formation in their arteries, as opposed to the other group with lower levels of blood lutein.   It was shown that the lesser lutein-rich plant foods they consumed, the more clogged their arteries. Perhaps more studies are needed to confirm this observation.

 

Another interesting observation is that after the researchers tested effects of lutein on human arteries that were surgically removed, there were fewer white cells present within the arteries after lutein supplementation was added compared to the controls. We know that the presence of white cells is suggestive of   an inflammatory response, and a subsequent blockage of the arteries which has no link to high or low blood cholesterol levels.

This may suggest the actions of free radical damage prior to atherosclerotic plaques and lesions.