Oxidative stress is a well-known cause of thyroid eye disease. Although antioxidants have long been shown to improve symptoms, the exact mechanism hasn’t been understood until now.
Animal Study of the Oxidative Ocular Protection of Catechins
In a study from the University of Hong Kong, researchers conducted animal studies evaluating the effects of catechins in green tea on eye diseases. The researchers measured catechin levels for up to 20 hours after ingestion. They discovered elevated catechins in the animals’ cornea, retina, vitreous humor and aqueous humor and a decrease in cytokine levels. Elevated catechins were not observed in the choroids sclera or the plasma. Cytokines and TSH receptor antibodies both contribute to oxidative stress and the development of Graves’ ophthalmopathy, which is also called thyroid eye disease (TED). The Hong Kong researchers concluded that green tea consumption and also green tea supplements could benefit the eye against oxidative stress (Chu et al, 2010).
Catechins are especially effective because they offer many cytoprotective properties. In particular catechins inhibit pro-inflammatory cytokines and growth factors that induce increased vascularization.
Antioxidant Agents Show Benefits in Graves’ Ophthalmopathy
In a small study of antioxidants involving 11 patients with TED, Greek researchers found that nine patients (82 percent) showed improvement of mild to moderately severe Graves’ ophthalmopathy compared to three patients (27 percent) in the control group. The patients were treated with the antioxidant B vitamin, nicotinamide. No side effects were observed by the patients using antioxidants, and patient satisfaction was reported to be high (Hondur et al, 2000).
In another study from the Gazi University Medical School in Turkey, orbital fibroadipose tissue was surgically removed from patients during orbital decompression. Using the disease activity index, all of the cases represented moderate to severe Graves’ ophthalmopathy. This tissue was compared to orbital tissue removed from patients with no evidence of thyroid or autoimmune disease. Tissue from the Graves’ patients showed significantly increased levels of enzymes involved in oxidative stress. Levels of natural antioxidants such as glutathione were significantly diminished. The researchers showed that while antioxidant activity in the orbital cavity is increased in Graves’ ophthalmopathy oxidative stress is so severe that it depletes the natural tissue antioxidants and leads to oxidative tissue damage (Hondur et al 2008).
Benefits from Anti-Thyroid Drugs on TED
Researchers from India have also shown that correcting thyroid hormone levels in Grave’s patients by using anti-thyroid drugs significantly reduces reactive oxygen species and oxidative stress. While anti-thyroid drugs such as methimazole have long been known to offer protection against Graves' ophthalmopathy, this study explains the reason for these benefits. However, even though anti-thyroid drugs reduce oxidative stress in the orbital cavity, the levels of enzymes involved in oxidative stress still remain higher than those of normal subjects. Reductions in natural antioxidants such as glutathione are suspected of being related to the deficiencies of essential antioxidant micronutrients, such as zinc, copper, and selenium, in the Indian population. The researchers concluded that antioxidant supplements may be as important as anti-thyroid drugs in reducing symptoms in Graves’ ophthalmopathy (Kaur et al 2010).
Sources:
Chu, Kai On, Kowk Chan, Chi Wang, Ching Chu, Wai Ying Li, Kwong Choy, Michael Rogers and Chi Pang. 2010. Green Tea Catechins and Their Oxidative Protection in the Rat Eye, Journal of Agricultural and Food Chemistry, 58(3) Jan: 1523-34.
Bouzas, Evrydiki, Pangagiotis Karadimas, George Matorakos, and Demetrios Koutros. 2000. Antioxidant Agents in the Treatment of Graves’ Ophthalmopathy. American Journal of Ophthamology, 129(5); May: 618-622.
Hondur A, O Konuk, A Dincel, A Bilgihan, M Unal and B Hasnresoglu. 2008. Oxidative stress and antioxidant activity in orbital fibroadipose tissue in Graves’ ophthalmopathy. Current Eye Research, 33(5), May: 421-427
Kaur, A, S Pandey, S Kumar, A Medhi, and A Mishra. 2010. Oxidative stress profile in Graves’ ophthalmopathy in Indian patients. Orbit, 20(2) April: 97-101.
Elaine Moore - I'm a retired medical technologist and medical writer with more than 30 years experience working in hospital laboratories. Currently, I ...
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