Nutrition for Eye Health (Eye of the Beholder)

Retinal Mayhem

With its importance to vision, retinal damage is a sore spot for eyesight. While macular degeneration is the common cause of vision loss relative to retinal problems, diabetes can eventually damage the circulation in the eye to the point of weakened and leaking blood vessels. This causes swelling, called edema, in the eye. If this edema is close to the center of the retina, vision loss can occur. Diabetic retinopathy afflicts more than 4 million Americans and can cause blindness.

It is a given that supplements shown to support the integrity of blood vessels in diabetes would be useful in inhibiting the development of diabetic retinopathy, but some nutritional ingredients have exhibited particular benefits to this eye complication.

As oxidative damage and growth factors are implicated in the pathology of diabetic retinopathy, research has focused again on the macula’s two antioxidant carotenoids, lutein and zeaxanthin. A 2008 animal study at Kresge Eye Institute, Detroit, discovered zeaxanthin significantly inhibits abnormalities associated with the pathogenesis of diabetic retinopathy, including retinal oxidative damage and increased vascular endothelial cell growth factor and intercellular adhesion molecule (ICAM).²⁸

University of Melbourne, Australia, scientists stressed the relationship between carotenoids and diabetic retinopathy is nowhere near as well established as in AMD, but they found concentrations of lycopene, lutein and zeaxanthin were lower in retinopathy;²⁹ pro-vitamin carotenoids, such as beta-carotene, were not lower. In fact, a higher ratio of non-pro-vitamin A carotenoids to pro-vitamin A forms was predictive of a lowered risk of diabetic retinopathy. They suggested risk of retinopathy may be modulated by increased intake of lycopene and lutein.

Efforts to delay the onset of diabetic retinopathy may get a boost from a combination of antioxidants, according to researchers from Wayne State University, Detroit.³⁰ In their examination of an antioxidant combination (including alpha-tocopherol, N-acetyl cysteine, ascorbic acid, beta-carotene and selenium) on retinal health in diabetic rats and in vitro conditions, they found increased oxidative stress led to increased apoptosis of endothelial cells and pericytes, but antioxidant treatment helped inhibit microvascular apoptosis.

An extract of Ginkgo biloba (EGb 761) has also addressed factors in diabetic retinopathy. Adults with type 2 diabetic retinopathy receiving EGb 761 had significantly improved blood viscosity and viscoelasticity, leading to improved blood perfusion and improved retinal capillary blood flow.³¹ EGb 761 also helped stabilize retinal health and improve performance on color vision tests in teenagers with type 2 diabetes.³² Displaying its retinal range, ginkgo extract has even improved visual acuity in adults with dry AMD after six months of supplementation with EGb 761.³³

Counteract the Cataract

Another degenerative scourge in the eye is cataract, the clouding of the eye’s lens, resulting in low vision. It is the leading cause of blindness worldwide and pulls the dark curtain over the eyes of some 20 million Americans over the age of 40, according to the U.S. National Eye Institute (NEI). The usual treatment for cataract is surgery, with more than 1.5 million performed annually in the United States. The opacity blurring the eye’s lens (or its envelope) is due to the denaturing of lens proteins, which can be caused by chronic exposure to ultraviolet light or other radiation, as well as complications from other diseases, such as heart disease and diabetes.

Here again, the antioxidants step front and center, although not without some debate. A German review called the impact of antioxidants on cataract minimal in clinical trials, including the AREDS and REACT (Roche European American Cataract Trial) studies.³⁴

However, Swiss researchers noted while the AREDS trial did not show a benefit for cataract formation and the REACT trial showed only a small impact on cataract progression, the REACT intervention started earlier in the disease process.³⁵ This suggests timing of antioxidant intervention may be important in cataract, with earlier supplementation a better bet to curtail disease onset.

The antioxidant nutrients in AREDS have fared better individually. Vitamin C in high levels can minimize the effects of radical oxygen species (ROS), protecting endogenous antioxidants and the lens.³⁶ In addition to shielding RPE cells from blue light-induced DNA damage, vitamin C intake of at least 362 mg/d can drop the odds of cataract formation by 43 percent, compared to those with vitamin C intake below 140 mg/d.³⁷

Vitamin E administration has also helped slow the development of cataracts, especially those induced by selenite (oxidation) and UV light.^38,39 It seems vitamin E directly increases antioxidant activity and levels of endogenous antioxidants such as glutathione. An examination of data from the Nurses’ Health Study revealed an inverse association between the five-year change in nuclear density and duration of vitamin E supplement use.⁴⁰

Lycopene has also shown positive benefits in cataract research. A study of lycopene on human lens epithelial cells found the carotenoid can protect against osmotic stress linked to diabetic cataract development.⁴¹ Further, animal research has shown intraperitoneal or dietary lycopene can protect against both selenite- or galactose-induced cataracts, based on antioxidant mechanisms, including the restoration of endogenous superoxide dismutase (SOD) and catalase activities.⁴²

A slew of 2008 studies have provided some insight on antioxidant nutrients and cataract development. Among the results, prospective observational data from a large cohort of female health professionals showed higher dietary intakes of lutein/zeaxanthin and vitamin E from both food and supplements are associated with significantly decreased risk of cataract.⁴³ Another trial reported finding inverse associations between cataract development and vitamin C, zeaxanthin, lutein, lycopene, alpha-and-beta carotene, beta-cryptoxanthin, but not for alpha- or gamma-tocopherol.⁴⁴ Higher combined intake of antioxidants—vitamins C and E, beta-carotene and zinc—also demonstrated long-term protective associations against development of nuclear cataract in an older population from the Blue Mountains Eye Study.⁴⁵ Antioxidants may be better against one form of cataract, as a 2008 study reported lens events were less common in subjects taking a multivitamin/mineral formulation, but the nutrients had a reverse effect on development or progression of the two most visually important opacity subtypes, nuclear and PSC opacities.⁴⁶

Antioxidants from botanical sources are not to be overlooked in the fight against cataracts. According to a trial out of India, green tea extract has prevented lens opacification in enucleated rat lenses treated with selenite.⁴⁷ The researchers noted green tea extract managed oxidative stress and reduced the incidence of selenite cataract. A Chinese trial delivered similar results, as green tea extract curbed postcapsular opacity in cultured rabbit lens epithelial cells.⁴⁸

Continue...

Pages: Previous 1 2 3 4 5 Next