Tea And EGCG Effects On Cataracts

Cataracts, a clouding of the lens of the eye, is one of the primary causes of blindness in the world. Approximately half of all Americans over age 65 have cataracts (CDC).

While sunlight, smoking, diabetes, and steroid use can contribute to early development of cataracts, most cataracts are associated with aging.

Over the last decade, researchers have begun to study the effects of black tea, green tea, and EGCG from green tea extract on preventing the development of cataracts in the lens of the eye.

The cloudy vision from cataract lens opacity is associated with oxidative stress. Free radicals (singlet oxygen molecules) damage cells including the retina and lens of the eye. Much cataract research has concentrated on the protective effect of antioxidants like vitamin E, and special antioxidant chemicals from tea and EGCG (green tea) to stop the free radical damage.

• an animal study found significant cataract reduction when green tea extract was given for several days before and after the start of cataracts (Gupta SK, Green tea (Camellia sinensis) protects against selenite-induced oxidative stress in experimental cataractogenesis, Opthlamic Research, July 2002)

• both green and black tea given to rats slowed the progression of cataract development (Thiagarajan G, Antioxidant properties of green and black tea, and their potential ability to retard the progression of eye lens cataract, Experimental Eye Research, September 2001)

• a case-control study with cataract patients in India found that cataract patients had significantly lower nutritional intakes of tea, green leafy vegetables, fruit, and micronutrients, while also showing significantly higher intakes of animal products and fried foods

• cell studies of EGCG found that the strong antioxidant capacity of epigallocatechin gallate (EGCG from green tea) protected eye lens cells from apoptotic death from free radicals by modulating capsases, Bcl-2 family, MAPK, and Akt pathways

Ultraviolet light frequencies also create free radicals in the lens of the eye. One study found that caffeine prevented many chemical reactions to UV light that damaged the eye. This may explain why both high antioxidant green tea and EGCG, and black tea with higher caffeine levels have shown protective effects.

Diabetes is expected to reach epidemic proportions in the world within a few decades. Along with life-threatening damage, diabetes also can increase the risk of permanent damage to the eyes, including speeding up cataract formation.

• an animal study using a model for diabetes found that both green and black tea given daily caused significant reductions in cataract formation as well as reducing high blood sugar (Vinson JA, Black and green teas equally inhibit diabetic cataracts in a streptozotocin-induced rat model of diabetes, Journal of Agricultural and Food Chemistry, May 2005)

• several studies pairing vanadate to lower blood sugar with Lichee black tea extract to reduce diarrhea (a side effect of vanadate medication for diabetics) found complete prevention of cataracts in an animal diabetic model (Clark TA, Codelivery of a tea extract prevents morbidity and mortality associated with oral vanadate therapy in streptozotocin-induced diabetic rats, Metabolism, September 2004)

In industrialized countries, loss of vision due to cataracts can usually be restored with cataract surgery. In other areas, encouraging inexpensive antioxidant nutrients like daily tea and EGCG green tea may reduce the burden of cataract vision loss on the communities.