Scientists funded by the Agricultural Research Service (ARS) reported this month that consuming a "high glycemic-index" diet over a long period of time is associated with a higher risk of developing the early stages of a major eye disease--age-related macular degeneration, or AMD.
The study was led by Chung-Jung Chiu and Allen Taylor at the Jean Mayer USDA Human Nutrition Research Center on Aging in Boston, Mass., and is part of the Nutrition and Vision Project, a substudy of the federally funded Nurses' Health Study.
A high glycemic-index diet is a diet high in the type of carbohydrates that are quickly digested and absorbed, resulting in a rapid rise in blood glucose levels. The macula is a yellow pigmented spot, one-eighth-inch wide, in the center of the retina toward the back of the eye. AMD is one of the leading causes of irreversible vision loss among those aged 40 or older in the United States.
Study participants were 526 women aged 53 to 73 years who did not have a history of age-related maculopathy, the early form of AMD. The scientists assessed the participants for macular disease and classified the results. They then compared the results with long-term dietary information that had been collected using questionnaires over a 10-year period prior to the macular disease assessment.
When ranked into three groups from highest to lowest in terms of dietary glycemic index, the participants who were ranked highest were well over two times more likely to have macular pigment abnormalities as those ranked lowest. An abnormal level of macular pigment is an early indicator of macular degeneration. The macula is responsible for the maximum ability to receive light and distinguish images.
Although the data do not establish a causal relationship, they do indicate a new direction for further studies that may help prevent or delay the onset of macular disease.
ARS is the U.S. Department of Agriculture's chief scientific research agency.