July 7, 2009
Eye health may be related to brain health, a new study reports. Seniors who scored low on tests of thinking and memory appeared to be more likely to have the early stages of macular degeneration, an eye disease related to aging. The findings appeared in the Archives of Ophthalmology, a journal from the American Medical Association.
Age-related macular degeneration, or AMD, is the leading cause of severe vision loss among men and women in developed countries. The disease causes loss of the ability to see images in the center of the visual field, making it difficult or impossible to read, watch TV, drive or engage in other everyday tasks. Scientists aren't sure what causes macular degeneration, but risk factors include aging, cigarette smoking, family history and obesity.
Researchers have long suspected that macular degeneration and Alzheimer's disease may share a common pathway because of various similarities between the two conditions. First, both conditions involve similar changes in the brain and eye, including the buildup of protein fragments known as beta-amyloid. Second, the two diseases share common cardiovascular risk factors, like cigarette smoking and high blood pressure. Both AMD and Alzheimer's disease have been linked to an increased risk of stroke.
In the current study, researchers in Australia examined 2,088 men and women who ranged in age from 69 to 97. Participants underwent regular tests of thinking and memory as well as exams to assess for eye disease as well as high blood pressure and other conditions.
After controlling for factors like age, sex and race, the researchers found that the one-fourth of volunteers who scored lowest on cognitive tests were twice as likely to have early-stage eye disease. "In conclusion, we found an association between low cognitive function and early AMD in this older population," the authors wrote. "These data, along with others, provide further support that AMD and cognitive impairment may share similar causes and risk factors."
It is possible that both Alzheimer's and macular degeneration may be mediated, in part, through damage to blood vessels. Factors like smoking and high blood pressure, for example, which raise the risk for both disorders, can damage blood vessels throughout the body, including in the eye and brain. Other factors like inflammation may also contribute to both disorders.
Although macular degeneration has a strong genetic component, a growing body of research shows that healthy behaviors can lower risk. Several recent studies have shown that regularly eating foods like fish, nuts and olive oil may lower the risk of age-related macular degeneration. These same foods are high in heart-healthy fats called omega-3 fatty acids and, other studies suggest, may lower the risk of Alzheimer's as well. Leafy greens may also provide protection for eye health.
Other foods, like highly processed carbohydrates and baked goods and foods high in trans fats, have been linked to an increased risk of macular degeneration. Further studies are needed to determine whether changing an individual's diet or recommending supplementation could prevent or delay the development of AMD or Alzheimer's.
By 2020, as many as 3 million Americans are expected to have late-stage age-related macular degeneration. Two to three times as many are expected to have Alzheimer's disease.
Michelle L. Baker; Jie Jin Wang; Sophie Rogers; Ronald Klein; Lewis H. Kuller; Emily K. Larsen; Tien Yin Wong: "Early Age-Related Macular Degeneration, Cognitive Function, and Dementia: The Cardiovascular Health Study." Archives of Ophthalmology, May 2009, Volume 127 (No. 5): pages 667-673.