Summer 2001 Issue — Looking ahead with carotenoids
More than just food colorants, these important plant pigments may help preserve eyesight in old age

Dr Christine Gaertner and Martin Weidner

Cognis Nutrition and Health

< Back

Advances in science and medicine, coupled with improvements in nutrition and hygiene, have considerably raised average life expectancy in the developed world. Just one per cent of the world's population was aged 65 and above a century ago. This figure has already risen seven-fold and will increase to around 20% by the middle of the 21st century, according to Tom Kirkwood, professor of Medicine and head of the Department of Gerontology at the University of Newcastle.

A longer lifespan is generally considered 'A Good Thing' - but only if accompanied by good health. The reality, of course, is that many people in these extra years of life will fall victim to one or more age-related diseases that may rob them of their independence and significantly impair their quality of life. One such disease is Age-related Macular Degeneration (AMD), the principal cause of irreversible blindness among elderly population in the western world. Though incurable and largely untreatable, there is cause for optimism in terms of preventing the disease. An increasing number of epidemiological and clinical studies strongly suggest that the carotenoids lutein and zeaxanthin may offer protection against AMD - in fact, carotenoids and vision represents one of the fastest-growing topics for antioxidant research.

AMD

AMD is a degenerative disease affecting some 25-30 million people throughout the world. It is estimated that for France, Germany and the UK foe example, around a million people could develop the disease in each country. Early symptoms include blurred or distorted vision and, as the disease progresses, sufferers seen a blank patch or dark spot in the center of the sight. They are left with only peripheral vision making reading, writing and recognizing faces increasingly difficult. Apart from advanced age, risk factors include family history, excessive sun exposure and light-colored eyes.

As with many age-related diseases, oxidative or free radical damage is thought to be a key factor in the development of AMD. The body's in-built repair mechanisms, which fight such damage, become progressively less effective as we get older - signs of ageing can, in fact, be seen in the retinas of most over 50's. They manifest as pale yellow spots - cellular waste products called 'drusen'. For a significant minority, these early signs will develop into AMD.

The disease affects a pinhead-sized, central part of the retina called the macula. Located at the center of the retina where the incoming rays of light are focused, the macula is responsible for our sharpest vision. It contains the highest concentration of photoreceptor cells, which convert light into nerve signals, but these cells are particularly susceptible to free radical and blue light damage.

Carotenoid Protection

Carotenoids are the most ancient protectors against sunlight and were developed by photosynthetic bacteria when life first began - without carotenoids, our plant life would burn up soon after sunrise. Research increasingly suggests that they perform a similar function in humans, protecting tissues exposed to light - the skin and eyes - from UV-induced free radical damage. Two yellow carotenoids, lutein and zeaxanthin, appear to be by far the most significant for eye health. Lutein and zeaxanthin and their derivatives are the only carotenoids found in lens and retina (see Fig 1), and specifically in the macula, where they form a protective layer known as the 'macular pigment'. Research by Landrum & Bone has already shown that people with a lower density of macular pigment are at greater risk of AMD. (1)

While additional carotenoids are present in other eye tissues, a recent study by Bernstein and colleagues from the University of Utah School of Medicine and the University of Maryland (2) - together with earlier findings by Hammond et al (3) - strongly suggests there are specific and critical reasons for the very selective concentration of lutein and zeaxanthin, especially in the macula region of the retina.

Two main reasons that have been suggested are first, the absorption of harmful blue light by the lutein/zeaxanthin-formed macula pigment, thus filtering or reducing the amount of such light able to reach the delicate retinal structures that are particularly sensitive to blue light.

Fig. 1

Antioxidant Action

The second reason is believed to be the antioxidant action of these carotenoids against free radicals.

A recent study conducted at the Cullen Eye Institute, Houston, Texas, provided evidence to support such an antioxidant role. Laurence Rapp and co-workers were able, for the first time, to confirm the presence of lutein and zeaxanthin in the photoreceptor cells, i.e. the outer segments of rods were the visual process takes place. Since the rod outer segment membranes are rich in polyunsaturated fatty acids and thus vulnerable to free radical damage, the carotenoids appear to be present exactly at the site where they would be most needed to perform their antioxidant function. (4)

Casual Link

Now, these researchers have made a casual link from Florida International University. Landrum, Bone and colleagues have found that the low levels of lutein and zeaxanthin seen in the retinas of AMD sufferers are indeed more likely to be a casual factor, rather than a destructive effect, of the disease. Their study examined retinas from 56 donors with AMD and 56 controls. Comparisons between the two groups showed that people with retinas in the highest quartile levels of lutein and zeaxanthin had an 82% lower risk of AMD than people in the lowest quartile levels. When the data was analyzed using statistical models, the results were consistent with a theoretical model that assumed that low retinal lutein and zeaxanthin are risk factors for AMD, rather than with a model that assumed they were a consequence of AMD. (5)

"We now have important evidence which brings us closer to making the statement that a low level of lutein and zeaxanthin in the retina may be one of several risk factors for AMD", said Dr. Bone. "Therefore, while there is no cure for this progressive condition, supplemental lutein might offer some protection for our ageing population. Future studies will help clarify which variables, such as diet and lifestyle, affect risk for AMD". One such study is Eureye, a multi-center study of prevalence and risk factors in elderly European populations. Researchers are investigating the effects on risk of AMD of diet (including antioxidant intake), lifetime residence and outdoor exposure, smoking habits, alcohol consumption, cardiovascular risk factors and quality of life. One thousand over-70's in each of seven European countries are being monitored for a three-year period with results due in February 2003.

Meanwhile, further research into macular pigment and risk of AMD has been carried out at Manchester Royal Eye Hospital (UK). Researchers there have recently confirmed that the two most important risk factors for AMD - age, and disease in the fellow eye - are associated with reduced macular pigment optical density (MPOD). Led by Stephen Beatty, they measured the optical density of macular pigment in 46 subjects aged 21-81 with healthy maculae, and in 9 healthy eyes known to be at high risk of AMD because of advanced disease in the fellow eye. Significantly less macular pigment was observed in the latter group. (6)

The researchers comment: "The hypothesis that macular pigment reduced the risk of development of AMD is particularly enticing because macular pigment is entirely made up of dietary origin, thus suggesting that the most common cause of blind registration in the western world could be delayed, or even averted, with appropriate dietary modification".

Lutein Supplements

Studies have already shown that increasing intake of lutein and zeaxanthin from either rich food sources such as spinach, broccoli or corn, or from supplements, can produce greater density of macular pigment. A recent Dutch study has confirmed that lutein supplements are indeed an effective means of achieving such an increase in density.

Scientists at the University Medical Center Utrecht found that plasma lutein levels increased five-fold with a daily dose of 20mg luteinesters, equivalent to 10mg free lutein. After 12 weeks' supplementation with a marigold-derived natural lutein ester product, eight male volunteers all showed an approximate 20% increase in macular pigment density. (7) The active ingredient in the supplement used in this study was the Cognis product, Xangold™.

Commenting on these results, Dr. John Landrum said, "This study is important because it provides additional evidence that lutein supplementation increases MP levels. Use of lutein supplements may provide important protection for individuals who have low levels of MP. The supplement used in this study increases both blood and macular levels of lutein, demonstrating that it is well absorbed".

< Back