Studies associate omega-3 fatty acid intake with reduced risk of macular degeneration
Two reports published in the July, 2006 issue of the AMA journal Archives of Ophthalmology revealed a decreased risk of developing age-related macular degeneration (AMD) associated with an increased intake of fish and omega-3 fatty acids (found in fish and other foods). Age-related macular degeneration occurs when the area at the back of the retina called the macula begins to degenerate, leading to central vision loss and even blindness among many individuals. It has been hypothesized that some of the risk factors for cardiovascular disease could contribute to the development of macular degeneration.
In one study, Brian Chua, BSc, MBBS, MPH of Westmead Millennium Institute and Vision Co-operative Research Centre in Sydney, Australia, and his colleagues utilized data from the Blue Mountains Eye Study, which enrolled 3,654 men and women aged 49 and older between 1992 and 1994. Dietary questionnaires completed by 2,895 participants at the beginning of the study provided information on fatty acid intake. Eye examinations were conducted upon enrollment and at the five year follow-up to determine the presence or progression of macular degeneration. Of those who submitted complete dietary questionnaires, there were 130 cases of early and 22 cases of late ARM.
Participants whose omega-3 polyunsaturated fat intake placed them in the top one-fifth of subjects were found to have a 59 percent lower risk of incident early age-related macular degeneration than those whose intake was in the lowest fifth. Consuming fish at least once per week was associated with a similar reduction in early ARM, while fish consumption at least three times per week was associated with a 75 percent reduction in late ARM. Although a higher intake of polyunsaturated fat from other sources has been associated with ARM in other studies, the current research did not find this association.
The study was, to the author’s knowledge, “The first cohort study of longitudinal association between dietary fat intakes and incident ARM in a representative older population.”
In another study, Johanna M. Seddon, MD, ScM, of the Massachusetts Eye and Ear Infirmary, in Boston, and colleagues evaluated macular degeneration risk factors among twins enrolled in the National Academy of Sciences—National Research Council World War II Veteran Twin Registry. Eye examinations, food frequency questionnaires, and telephone interviews concerning demographic characteristics, smoking status, health history, and other factors were administered to 681 men. Two hundred twenty-two participants were found to have intermediate or late state macular degeneration.
Current smoking was associated with a 1.9-fold increase in the risk of having AMD, and past smoking with a 1.7 increase compared to those who never smoked. For men whose omega-3 fatty acid content was among the top 25 percent of participants there was a 45 percent reduced risk of macular degeneration compared with those whose intake was lowest. Eating fish at least twice per week reduced AMD risk by 36 percent compared to those who consumed less than one serving per week.
The authors conclude that "About a third of the risk of AMD in this twin study cohort could be attributable to cigarette smoking, and about a fifth of the cases were estimated as preventable with higher fish and omega-3 fatty acid dietary intake. Age-related macular degeneration is a common eye disease in older persons, smoking is a common avoidable behavior and dietary habits are modifiable; therefore, a proportion of visual impairment and blindness due to AMD could be prevented with attention to healthy lifestyles."
The best approach to ensuring protection against the onset of age-related macular degeneration and the possible treatment of the condition involves an understanding of some of the main circumstances under which the condition arises. These are presented below followed by the recommended nutritional therapies for each problem.
1. A reduction in the essential macular pigments, lutein and zeaxanthin, critical for the protection and proper functioning of the mechanisms required for the detection and imprinting of the light signals that come into the macula from the outside world.
As lutein and zeaxanthin are the essential pigments within the macula, it is critical to replenish them as they become depleted through the aging process. Consumption of foods rich in these substances is especially important since they have a direct affect on macular pigment density. When the pigment in the macula is denser, retinal tearing or degeneration is less likely. Lutein and zeaxanthin are found in yellow or orange vegetables, in dark leafy greens, and in fruits with yellow or orange hues. Egg yolk is a good source of lutein. Dietary supplements of lutein and zeaxanthin are recommended.
2. A reduction in antioxidant levels within the retina and surrounding structures that make possible the presence and proliferation of free radicals that damage these structures and keep them from optimal functioning.
An increase in damaging free radical activity occurs through smoking, exposure to second-hand smoke, in diets high in saturated fats, cholesterol, and low in the “good fats” found in fish, whole grains and legumes. Smoking and high-fat diets are associated with AMD.
Decreased levels of natural antioxidants in the healthy eye are associated with AMD. Some of these essential natural antioxidants are glutathione, vitamin C, and the carotenoids, lutein and zeaxanthin. Dietary supplementation with these antioxidants protect against the progression of AMD. Other recommended antioxidants to protect the macula and retina include vitamin A, vitamin E, L-carnosine, taurine, lipoic acid, selenium, zinc (with copper), grape-seed extract, and coenzyme Q10.
3. The onset of ocular atherosclerosis involves blockages in the choroidal blood vessels that adversely effects the functioning of the retina and, particularly, the macula.
Damaged blood vessels in the eye are associated with the onset of AMD. Blockages of these blood vessels, known as ocular atherosclerosis, raises blood pressure, creates deposits under the macula, and abnormal growth of blood vessels into the retina (choroidal neovascularization). The result is severe and debilitating neovascular AMD.
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