AMD results in partial or total blindness in 7 to 15% of the elderly, according to the Eye Diseases Prevalence Research Group. "Dietary changes may be the most practical and cost-effective prevention method to combat progression of AMD," says Allen Taylor, PhD, director of the Laboratory for Nutrition and Vision Research at the USDA HNRCA. "It is surprising there is so little attention focused on the relationship between AMD and carbohydrates."
The current study, published in the October issue of the American Journal of Clinical Nutrition, builds on a recent analysis by Taylor and colleagues that found men and women older than 55 who consumed diets with higher-than-average dietary glycemic index foods appeared to have an increased risk for both early and later stages of AMD.
Dietary glycemic index is a scale used to determine how quickly carbohydrates are broken down into blood sugar, or glucose. Foods with a high glycemic index are associated with a faster rise and subsequent drop in blood sugar. Refined carbohydrates like white bread and white rice have high glycemic indices. Whole wheat versions of rice, pasta and bread are examples of foods with low glycemic indices.
In the present study, Taylor and colleagues analyzed diet questionnaires completed by 4,757 non-diabetic men and women participating in the nationwide Age-Releated Eye Disease Study (AREDS). The eight-year AREDS study enrolled participants between the ages of 55 and 80 with varying stages of AMD. Taylor and colleagues examined the participants' carbohydrate intake over a one-year period and used the data to calculate the participants' dietary glycemic index.
"Our data showed those people in the high-glycemic-index group were at greater risk of AMD progression, especially those already in the late stages," says first author Chung-Jung Chiu, DDS, PhD, scientist in the Laboratory for Nutrition and Vision Research at the USDA HNRCA and assistant professor at Tufts University School of Medicine. "Participants who consumed the most refined carbohydrates were 17 percent more likely to develop blinding AMD than the group that consumed the least."
According to the authors, public health officials believe the condition could spur a public health crisis in the United States by 2020, when they predict the cases of AMD-related vision loss will have doubled to three million.
"No one has been able to identify an effective noninvasive intervention that will slow the progression of AMD" says Taylor, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts and Tufts University School of Medicine. "We feel we have identified a risk factor that could postpone the debilitating loss of vision with very little economic or personal hardship. Based on our data, limiting refined carbohydrate intake, such as by limiting sweetened drinks or exchanging white bread for whole wheat, in at-risk elderly could reduce the number of advanced AMD cases by 8 percent in five years. This can equate to saving the sight of approximately 100,000 people."
The authors note that their findings warrant randomized controlled clinical trials.