Age-Related Macular Degeneration – Potential Roles for Nutraceuticals in its Prevention and Control

Many lines of evidence point to oxidative stress as a key pathogenic factor in age-related macular degeneration (AMD); the modestly positive results of the AREDS1 study – which evaluated supplemental zinc, vitamin E, vitamin C, and beta carotene in AMD patients provide confirmation for this view, while also pointing to a potential role for nutraceuticals in prevention and management of this syndrome. Xanthophyll carotenoids, the key components of macular pigment, appear to play a crucial physiological role in protecting the macula from light-induced oxidative damage, and docosahexaenoic acid (DHA), a major constituent of photoreceptor outer segments, may be needed for optimally efficient rhodopsin function and photoreceptor survival. Epidemiological studies demonstrate reduced risk for AMD in people with increased dietary intakes and tissue levels of long-chain omega-3s and of the xanthophylls, and the ongoing AREDS2 study will determine whether supplementation with these agents can aid AMD control. Ancillary antioxidant measures may also prove useful in this regard. Phase 2 inducers (including lipoic acid and a wide range of phytochemicals), melatonin, and N-acetylcysteine, may have the potential to boost retinal expression of glutathione and of a number of antioxidant enzymes. In light of the recent discovery that the chief phytochemical in spirulina can inhibit NADPH oxidase – a likely source of retinal oxidative stress – spirulina supplementation may merit consideration in AMD management. The recent WAFACS study demonstrates important primary prevention of AMD with high doses of the B vitamins folate, pyridoxine, and cyanocobalamin; conceivably, this reflects the ability of high-dose folate to boost nitric oxide production by oxidatively-stress choroidal vessels. Suggestive evidence that estrogen may reduce risk for wet AMD raises the possibility that soy isoflavones could likewise provide benefit in this regard. It is not unreasonable to hope that comprehensive nutraceutical strategies that are rational and complementary will someday demonstrate very considerable efficacy in the prevention and control of AMD. Moreover, there is reason to suspect that lutein and zeaxanthin may aid prevention of cataract (as they provide antioxidant protection for the lens) while helping to combat visual fatigue and glare. Pathophysiology of AMD Age-related macular degeneration (ARMD, AMD, ARED), or aging macula disease, is the leading cause of vision loss and partial blindness among elderly Americans 60 and older. This group represents an increasingly larger percentage of the general population; hence vision loss from macular degeneration is a growing problem. Men and women are about equally affected, and the incidence of AMD in blacks is lower than it is in whites. AMD is the most common cause of visual impairment in the developed world.