Dietary Glycemic Index Tied to Risk of Age-Related Macular Degeneration

Poor dietary carbohydrate quality as defined by the dietary glycemic index — a modifiable risk factor — may increase the risk of age-related macular degeneration (AMD), according to study results.

"AMD appears to share several carbohydrate-related mechanisms and risk factors with diabetes-related diseases, including retinopathy and cardiovascular disease (CVD)," write Dr. Allen Taylor, of Tufts University, Boston, Massachusetts, and colleagues. "However, to date, only one small study has addressed this issue."

To investigate further, the researchers conducted a cross-sectional study of 4099 participants, aged 55 to 80 years, in the Age-Related Eye Disease Study (AREDS).

The team classified a total of 8125 eyes at baseline into one of five AMD groups based on the size and extent of drusen, the presence of geographic atrophy, and neovascular changes.

The dietary glycemic index (dGI) for each subject was calculated from the weighted average of the glycemic index scores for each item on a food questionnaire. The glycemic index values for the foods "were either derived from published values based on white bread as the reference food or were imputed from glycemic index values of comparable foods."

The investigators report that eyes in the fourth and fifth quintiles of dGI had a significantly "or suggestively" higher risk of large drusen, geographic atrophy, and neovascularization compared to eyes in the first quintile. There was a significant positive association between dGI and severity of AMD (p for trend <0.001).

"There was a 49% increase in the risk of advanced AMD (geographic atrophy plus neovascularization) for persons with a dGI higher than the sex median," Dr. Taylor’s team found. They calculate that 20% of prevalent cases of AMD would have been prevented if subjects had consumed diets with a dGI below the median.

Am J Clin Nutr 2007;86:180-188.