Turmeric and Green Tea Share a Special Property

Antioxidants Combat
Age-Related Macular
Degeneration

A variety of antioxidants—vitamins, minerals,
polyphenols, carotenoids, and more—is better than any one
By Will Block


Courtesy of Guide Dogs for the Blind, San Rafael, CA
common sight on the streets of San Rafael, California (in Marin County, just north of San Francisco), is blind people with guide dogs, mostly Labrador retrievers, golden retrievers, and German shepherds. To a newcomer, it must seem as though San Rafael had been struck by a terrible plague. The truth, however, is more benign: the city is home to the nonprofit charitable organization Guide Dogs for the Blind,* and the pooches are being trained for the awesome responsibilities they will assume in acting as the eyes—and lifeguards—of their afflicted owners.


*For information about this wonderful organization (especially if you know someone who is legally blind), see www.GuideDogs.com, which even has downloadable videos of romping puppies that will grow up to be canine miracle workers. They accept contributions (the organization, not the puppies).


To those who can see the novice dogs being trained by their patient handlers—or the graduate dogs with their new owners, being trained in how to work with them—it’s a sight both heartwarming and inspiring. The bond between man and beast is almost supernatural.

Wet AMD Is the Worst

In last month’s issue of Life Enhancement, we wrote about age-related macular degeneration (AMD), an incurable eye disease that robs people of their central vision—the type of vision required to see fine details, such as the letters in these words or the features of a child’s face. (See “Can Age-Related Macular Degeneration Be Prevented?” – March 2007.) Although they typically retain their peripheral vision, many victims of AMD are sufficiently impaired in functional mobility to be declared legally blind.

About 90% of such cases are due to the “wet” form of AMD, in which the retina in the area of the macula (a small, yellowish spot near its center) is irreparably damaged by a process called neovascularization, which is the growth of new blood vessels where they don’t belong. The vessels are fragile and leak fluid, which damages or kills retinal cells. Neovascularization is a special case of angiogenesis, the formation of new blood vessels. In wet AMD, it occurs in a thin layer of tissue called the choroid, which lies just beneath the retina.

Dry AMD Is Bad Enough—And There’s No Magic Bullet

The other, less severe, type of AMD is the “dry” form, which entails the formation of drusen beneath the retina. Drusen are small, fatty deposits that gradually degrade retinal function, causing visual impairment and, sometimes, legal blindness. About 85–90% of all cases of AMD are of the dry type. Overall, AMD is the leading cause of blindness in people over 50 in the developed world; its incidence in the United States is expected to increase by 50% by 2030.1

The thought of blindness is a nightmare, and it’s worth every effort to prevent it. The message of last month’s article was that it’s probably best to use a supplement containing all the natural chemical agents that are known to benefit our eyes in one way or another. A cynic might say that this is the “throw everything but the kitchen sink at it” approach, and there is merit in that charge. More importantly, however, there is merit in the approach itself (provided, of course, that there’s a valid scientific basis for each of the agents being used). When we can’t point to one agent and say, “This is the magic bullet that will help prevent AMD,” we must try everything plausible and hope that some of it helps.

With Antioxidants, the More Variety, the Better

So instead of a single-bullet medicinal rifle shot, we use buckshot, hoping that the additive (and perhaps synergistic) effects of all the individual chemical “pellets” will do the trick. And what are those pellets? Well, many of them are antioxidants, because oxidative stress—the damaging effects of reactive oxygen species, including free radicals—is implicated in AMD, as it is in most age-related diseases, and in the aging process itself. And here the “kitchen sink” strategy is justified by scientific evidence. According to Dr. Julie Mares of the University of Wisconsin–Madison Medical School,2

Overall, there is a clear trajectory of lower risk for AMD that is associated with diets higher in several antioxidants. … A combination of antioxidants seems to be more consistently associated with lower risk for early or late AMD than single nutrients. … it makes sense that optimal functioning requires the availability of numerous antioxidants. Foods provide an even greater array of antioxidants than supplements. … Thus, antioxidant-rich diets are also likely to be nutritionally varied and provide a wide array of other known and unknown nutrients and nonnutritive food components that might protect against AMD. [Italics ours]

Although her emphasis was on food, Dr. Mares also discussed the value of antioxidant supplements, which is well established, especially for vitamin C, vitamin E, beta-carotene (a vitamin A precursor), and zinc.3,4 Her comments (which would probably apply as well with regard to all the other chronic diseases for which antioxidants reduce risk) drove home the point that supplements are just that: supplements, not substitutes for a healthy diet, which undoubtedly contains many valuable nutrients we haven’t even discovered yet.

Let’s now look at a few nutrients we do know about, beginning with two that have an exceptionally important property in terms of potential action against AMD: they inhibit angiogenesis, which, as we saw above, underlies wet AMD.

Turmeric Inhibits Angiogenesis

The Indian spice turmeric (Curcuma longa), often called “the spice of life,” has long been known for its antioxidant, anti-inflammatory, and antitumor properties, which are attributed mainly to the polyphenolic compound curcumin and a group of related compounds called curcuminoids. In mouse studies, curcumin has been effective primarily against skin and colon cancers, perhaps because it works best by direct contact (it’s poorly absorbed into the circulation, and once there, it’s rapidly metabolized). It has also shown promise against human cancers, primarily of the gastrointestinal tract.5

In a laboratory study with human umbilical vein endothelial cells (HUVECs), curcumin blocked the cell proliferation that could contribute to angiogenesis and tumor growth.6 In a study with mouse corneas, curcumin and some curcuminoids were found to inhibit artificially induced neovascularization.7 Similar results were obtained in a study with rabbit corneas.8 Finally, oral administration of curcumin (1125 mg/day) was found in a human clinical trial to be helpful for chronic anterior uveitis (an inflammation of the front part of the eye), indicating that enough of it can reach the eye to do some good there.9 The main advantage of curcumin was that it acted like a corticosteroid, but without any of the side effects of those powerful drugs.

Green Tea Also Inhibits Angiogenesis

Another potentially beneficial product for AMD is green tea (Camellia sinensis), which contains a class of polyphenolic antioxidants called catechins, the most important of which is epigallocatechin gallate, or EGCG. The documented health benefits—including cancer prevention—of green tea are too numerous to recite here. One of the more recently discovered ones comes from a study, using HUVECs, that sought to elucidate the (or a) mechanism of green tea’s anticancer activity.10 The researchers found that the catechin-rich extract inhibited angiogenesis, a process upon which the growth of tumors critically depends. Similar results were obtained in another study, in which pure catechins were used instead of a green tea extract, and bovine aortic endothelial cells instead of HUVECs.11

Zinc Is Vital for Our Eyes

Finally (although there’s much more we could write about, such as the extremely important antioxidant carotenoids lutein and zeaxanthin), let’s take a quick look at the trace element zinc. This mineral is found in high concentrations in our eyes, particularly in the retina and the choroid. Zinc plays an integral role in maintaining normal ocular function via several mechanisms, including an antioxidant effect. A deficiency or even suboptimal levels of zinc may influence the development and progression of several chronic eye diseases.12

The role of zinc in preventing AMD is still unclear, but in a major study of antioxidants and eye disease, it was found that those patients who were randomly assigned to receive zinc had a significantly reduced mortality rate compared with those who did not take zinc.13

Woof!

At the risk of belaboring the obvious, your eyesight is precious. Not quite as obvious, but true, according to experts in the field, is that the value of antioxidants (whether from food or supplements) in preventing AMD depends on the stage of the disease. They’re far more effective in slowing or halting its progress in the early stages than later on, when they’re fighting a decidedly uphill battle. The same could probably be said of just about any preventive measure for any disease—it’s common sense.

As Benjamin Franklin said, “An ounce of prevention is worth a pound of cure.” Think about that the next time you see a guide dog. As much as we love and admire those sweet, noble creatures, we would never want to have to own one.

Odds and Ends about Turmeric and Tea

Remember litmus paper, a staple of high school chemistry labs? It had a nineteenth-century predecessor, turmeric paper, which was used worldwide to test solutions for alkalinity. (If litmus hadn’t come along, we might today be talking about political “turmeric tests.”) Turmeric had long served as an orange-yellow textile dye in East Asia, and it imparts the characteristic yellow color to curries and many mustards.

Turmeric is featured in many ancient Indian ceremonies and Malaysian myths. According to legend, it has the power to repel crocodiles. There are, however, no actual data on how many lives have been saved in this way, so we remain a tad skeptical. (What a pity that Steve Irwin is no longer with us to give an authoritative answer. Not that he ever wanted to repel crocodiles—quite the contrary!) In any case, modern science has confirmed the validity of several of turmeric’s traditional medicinal uses, especially as an anti-inflammatory.

Tea too has an ancient history of medicinal use throughout the Orient. Most potent are white tea and green tea, which are made without the partial fermentation process that produces oolong tea, or the full fermentation that produces black tea. Fermentation destroys most of the leaves’ natural catechins, the antioxidant polyphenols to which most of tea’s healing properties are ascribed (the “rock star” here is EGCG). There is a tradeoff, however: some of the catechins are polymerized to new compounds called theaflavins and thearubigins, and they too have significant therapeutic value.

Legend has it that tea was discovered in 2737 B.C., when some tea leaves fell from a tree into a cup of hot water held by a fellow named Shen Nung, who just happened to be the emperor of China. (Nothing like that could have happened to a mere peasant, right?) He was so pleased with the aroma and taste that he believed the tea had come from heaven. Thus was born the world’s second most consumed beverage (after plain old water), not to mention a vast historical and cultural legacy associated with the wondrous brew. The virtues of tea are embodied in the Chinese proverb, “The wisdom of ten thousand universes can be found in a cup of tea.” Wow.

Until about three centuries ago, by the way, tea was pronounced “tay,” which explains why it doesn’t seem to rhyme properly in some old English poetry (it did then, though). The word comes from the Dutch thee, from the Malay teh, from the Chinese (Amoy) te, all of which are pronounced (more or less) … tay.

References

  1. Mares JA, Moeller SM. Diet and age-related macular degeneration: expanding our view. Am J Clin Nutr 2006;83:733-4.
  2. Mares JA. Potential value of antioxidant-rich foods in slowing age-related macular degeneration. Arch Ophthalmol 2006;124:1339-40.
  3. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta-carotene, and zinc for age-related macular degeneration and vision loss: AREDS Report No. 8. Arch Ophthalmol 2001;119:1417-36.
  4. van Leeuwen R, Boekhoorn S, Vingerling JR, Witteman JCM, Klaver CCW, Hofman A, de Jong PTVM. Dietary intake of antioxidants and risk of age-related macular degeneration. JAMA 2005;294:3101-7.
  5. Cheng AL, Hsu CH, Lin JK, et al. Phase I clinical trial of curcumin, a chemopreventive agent, in patients with high-risk or pre-malignant lesions. Anticancer Res 2001;27:2895-900.
  6. Singh AK, Sidhu GS, Deepa T, Maheshwari RK. Curcumin inhibits the proliferation and cell cycle progression of human umbilical vein endothelial cell. Cancer Lett 1996;107:109-15.
  7. Arbiser JL, Klauber N, Rohan R, van Leeuwen R, Huang MT, Fisher C, Flynn E, Byers HR. Curcumin is an in vivo inhibitor of angiogenesis. Mol Med 1998;4(6):376-83.
  8. Mohan R, Sivak J, Ashton P, Russo LA, Pham BQ, Kasahara N, Raizman MB, Fini ME. Curcuminoids inhibit the angiogenic response stimulated by fibroblast growth factor-2, including expression of matrix metalloproteinase gelatinase B. J Biol Chem 2000;275:10405-12.
  9. Lal B, Kapoor AK, Asthana OP, Agrawal PK, Prasad R, Kumar P, Srimal RC. Efficacy of curcumin in the management of chronic anterior uveitis. Phytother Res 1999;13:318-22.
  10. Kojima-Yuasa A, Hua JJ, Kennedy DO, Matsui-Yuasa I. Green tea extract inhibits angiogenesis of human umbilical vein endothelial cells through reduction of expression of VEGF receptors. Life Sci 2003;73:1299-1313.
  11. Lamy S, Gingras D, Béliveau R. Green tea catechins inhibit vascular endothelial growth factor receptor phosphorylation. Cancer Res 2002; 62:381-5.
  12. Grahn BH, Paterson PG, Gottschall-Pass KT, Zhang Z. Zinc and the eye. J Am Coll Nutr 2001;20(2):106-18.
  13. Age-Related Eye Disease Study Research Group. Associations of mortality with ocular disorders and an intervention of high-dose antioxidants and zinc in the Age-Related Eye Disease Study: AREDS Report No. 13. Arch Ophthalmol 2004;122:716-26.


Will Block is the publisher and editorial director of Life Enhancement magazine.

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