Carbohydrates may play a role in debilitating eye disease

A person’s risk of developing age-related macular degeneration, one of the leading causes of vision loss in older adults, may depend on the quality—rather than the quantity—of carbohydrates in the diet, according to nutrition researchers at Tufts.

In analyzing data from a sub-group of participants in the Nurses’ Health Study who were enrolled in the Nutrition and Vision Program, scientists at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) looked at the total amount of carbohydrates consumed over 10 years and the dietary glycemic index. A high glycemic-index diet is one that is rich in foods that are converted more rapidly to blood sugar in the body, such as white bread and French fries, than low glycemic-index foods, such as lentils and yams.

“Women who consumed diets with a relatively high dietary glycemic index had a greater risk of developing signs of early age-related macular degeneration when compared with women who consumed diets with a lower dietary glycemic index,” said lead author Dr. Chung-Jung Chiu, a scientist in the HNRCA Laboratory for Nutrition and Vision Research and an assistant professor at the School of Medicine.

High total carbohydrate intake, however, did not significantly increase the risk for age-related macular degeneration.

“In other words, the types of carbohydrates being consumed were more important than the absolute amount,” said Allen Taylor, director of the Laboratory for Nutrition and Vision Research and a senior author on the study, which was published in April in the American Journal of Clinical Nutrition.

Age-related macular degeneration is irreversible and primarily affects central vision. The disease is caused by the gradual breakdown of light-sensitive cells in the region of the eye’s retina called the macula. It is estimated that 1.75 million Americans over age 40 have some manifestation of the disease.

The Tufts researchers examined the eyes of more than 500 women between the ages of 53 and 73. They looked for changes indicative of early age-related macular degeneration. They also analyzed the women’s diets, which were reported in questionnaires that had been administered periodically over the 10 years preceding their eye exams.

“Dietary glycemic index may be an independent and modifiable risk factor for early age-related macular degeneration,” Taylor said. “The likelihood of having abnormalities characteristic of [the disease] on an eye exam more than doubled for women who consumed diets with the highest glycemic index, regardless of other factors already known or suspected to increase the risk, such as age, high blood pressure, cigarette smoking and obesity.

“We cannot say, based on these data, whether or not consuming a diet with a high glycemic index causes age-related macular degeneration,” Taylor said.