High-GI Diet Connected to AMD

Age-related macular degeneration (AMD) is a primary cause of blindness, particularly as people advance in years. AMD, which has no cure and limited treatment options in its later stages, afflicts more than 10% of people over 80 years of age. Although previous research has demonstrated a connection between vitamin A deficiency and higher AMD risk, the results of a new study, recently published in the April issue of the American Journal of Clinical Nutrition (2006; 83:880-886), have shown a new dietary link to increased AMD risk: a high-glycemic diet.

This study was led by Dr. Chung-Jung Chiu, scientist III, and Allen Taylor, Ph.D., senior scientist and director, both of the Jean Mayer USDA Human Nutrition Research Center, Boston. This work was part of the Nutrition and Vision Project, a substudy of the Nurses' Health Study, and funded by USDA's Agricultural Research Service.

The researchers studied the diets of 526 women enrolled in the Nurses' Health Study. The participants were all aged 53 to 73 and did not have a history of maculopathy, a pathological condition that presages AMD. The scientists then evaluated dietary data collected over a 10-year period and calculated a corresponding glycemic index (GI) for each individual. Results showed that development of AMD was not affected by body-mass index, alcohol consumption, smoking or total carbohydrate intake. However, AMD proved more commonly tied to carbohydrate-rich, high-GI diets.

Julie A. Mares, Ph.D., and Dr. Suzen M. Moller, both of the Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, also contributed to this subject via their editorial in the same issue of the American Journal of Clinical Nutrition (733-734). The authors mention the study by Chiu et al. and then go on to note that the relationship between AMD and high-GI diets might result from an associated dietary lack of antioxidant nutrients from fruits and vegetables, like vitamins C and E, carotenoids like lutein and zeaxanthin, as well as zinc. "Diet is potentially one of the most cost-effective strategies to prevent the development of AMD, the incidence of which is expected to increase by 50% by 2030 in the United States," write the authors.

In their editorial, Mares and Moller also note that more research is required to further understand the relationship between diet and AMD risk. Notably, Chiu et al. observed a connection between GI and an indicator of the early stages of AMD--the presence of pigmentary abnormalities. "Early AMD is a strong predictor of developing advanced AMD," note the authors. Therefore, they hypothesize that slowing development of early AMD might reduce the number of advanced AMD cases.