(NaturalNews) A new study has investigated the protection afforded by the flavonoid quercetin against macular degeneration. The macula is the yellowish, central part of the retina about 1.5 mm in diameter that produces central vision and color vision. Macular degeneration is the gradual, progressive destruction of the macula that results in lowered central visual acuity needed for most everyday activities, like reading this article. It leads to permanent blindness, and is the most common cause of blindness in people 50 to 60 years old and above. Approximately 10 million Americans are believed to suffer vision loss due to age-related macular degeneration (ARMD).
There are two types of ARMD: dry and wet. The dry type is much more common than the wet type and accounts for up to 90% of ARMD. In the dry type, the macula gradually thins with aging. The pigmented retinal epithelium, which is the dark-colored cell layer at the back of the eye essential for vision, is gradually lost. One of the first signs of ARMD is loss of color sensitivity and blurring or haziness while reading.
Previous reports have concluded that eating foods rich in lutein and zeaxanthin can help protect the macula, that obese individuals have lower amounts of macular pigment than non-obese people, and that people with very low body fat levels have a higher amount of carotenoids in their blood, which could lead to more pigment in the macula.
The Background of the Recent Report
The current research report states that oxidative stress plays a central role in macular damage, and that some previous studies have shown that intake of foods with a high level of antioxidants may lead to a lower risk of ARMD; "recommended supplementary antioxidants include vitamin C, vitamin E, beta carotene, and lutein".
Another group of antioxidants that may be protective are the bioflavonoids: "the large group of polyphenolic compounds that provide much of the color and flavor of plant foods". The most-studied bioflavonoid is quercetin, which is well known to be present in apples and onions, and has already been shown to have anti-allergic, anti-inflammatory, anti-carcinogenic, anti-viral, and anti-thrombotic properties. It is a strong antioxidant and free-radical scavenger.
The study used cultured human cells of the retinal pigmented epithelium treated with hydrogen peroxide as the oxidative stress agent. Oxidative damage was measured using a special histochemical staining procedure.
Cells treated with hydrogen peroxide alone (the control group) suffered significantly more damage than cells treated with hydrogen peroxide and quercetin. Intracellular glutathione (one of the body's intrinsic antioxidants) was not altered by hydrogen peroxide treatment or by quercetin (glutathione was measure as reduced GSH only in this study), showing that quercetin's protective effects might be independent of glutathione. (However, previous studies, which measured different forms and ratios of glutathione, have shown increased intracellular glutathione after addition of quercetin.)
The protective mechanisms of quercetin were demonstrated to be related to its ability to reduce the activity of caspase-3 and level of caveolin-1, both of which were induced by hydrogen peroxide.
Not too low, Not too high
Healthful circulating levels of quercetin (0.1 to 1 micromole) can be achieved by consuming 100 to 200 grams of onion a day. Other foods containing ample quercetin are listed as capers, ancho peppers, cranberries, fennel, cocoa, black currants, buckwheat, black tea, spinach, and wild greens.
Very high concentrations, 100 micromoles or higher, have been suggested in laboratory studies to induce chromosomal damage or cytotoxicity. So, "like many other especially lipid-soluble antioxidants, excessively elevated serum levels of quercetin may cause cellular injury." (These very high levels were produced in laboratory experiments, but could also probably result from taking too many supplements.)
Although this was an in vitro (test-tube) study, based on the present study's results and past findings, the authors conclude, "quercetin appears to be a candidate as food supplement in the prevention of early pathologic changes" in ARMD.
Journal, Research Facility
The study, reported in Investigative Ophthalmology & Visual Science, was carried out at the Department of Ophthalmology, Ludwig-Maximilians-Universitat, Munich, Germany.
John H. Cole has been editing medical manuscripts for publication in mainstream U.S. and European medical journals for the past 15 years in Japan. He also has a small English school in Gifu City, Japan. He believes that natural foods, superfoods, herbs, exercise, sunshine, good sleep, and avoidance of pollution are the answers to most people's health problems. He is a friend of nature.