High GI diet linked to poor eye health

Writing in the current issue of the American Journal of Clinical Nutrition , adds to earlier studies that reported a diet with high GI increased the risk of early AMD.

"Men and women who consumed diets with a higher glycemic index than average for their gender and age-group were at greater risk of developing advanced AMD," said corresponding author Allen Taylor.

"The severity of AMD increased with increasing dietary glycemic index."

AMD affects the central part of the retina called the macula, which controls fine vision, leaving sufferers with only limited sight.

AMD affects over 30m people worldwide, and is the leading cause of blindness in people over 50.

The new study analyzed data from 4,099 men and women participating in the nationwide Age-Related Eye Disease Study (AREDS).

Detailed dietary histories were obtained at the start of the study when participants were 55 to 80 years of age and had varying degrees of AMD.

AREDS was initially designed to assess the effect of high-dose antioxidant vitamins and zinc on the progression of AMD and cataracts, two of the leading causes of vision loss in older adults.

Taylor and co-workers report that consumption of a diet with a glycemic index above that of the average for the sex (77.9 for women, 79.3 for men) was associated with a 49 per cent increase in advanced AMD risk.

"Although carbohydrate quality was not the main focus in the AREDS, we were fortunate that the investigators had collected the dietary carbohydrate information we needed to do our analyses," said Taylor.

"Our findings suggest that 20 percent of the cases of advanced AMD might have been prevented if those individuals had consumed a diet with a glycemic index below the average for their age and gender," he added.

The glycaemic index measures how quickly certain foods release carbohydrates into the body, which then raise consumers' blood glucose levels.

High GI foods cause blood sugar levels to rise more rapidly.

The interest in the GI of foods and the digestibility of carbohydrates has increased considerably in recent years.

A number of studies suggest that a low GI and slowly digestible carbohydrates can contribute to the prevention of obesity and diabetes.

"Our results support our hypothesis that dietary glycemic index, which has been related to the risk of diabetes, is also associated with the risk and severity of AMD," said Taylor.

"It is possible that the type of damage produced by poor quality carbohydrates on eye tissue is similar in both diabetic eye disease and AMD," he added.

The researchers suggested that reduction of dietary glycemic index may be a relatively simply way of reducing the risk of AMD.

"However, additional studies are needed before we can recommend dietary carbohydrate management as a prevention strategy for AMD," concluded Taylor.

Source: American Journal of Clinical Nutrition July 2007, Volume 8, Number 1, Pages 180-188 "Association between dietary glycemic index and age-related macular degeneration in nondiabetic participants in the Age-Related Eye Disease Study."

Authors: C.-J. Chiu, R.C. Milton, G. Gensler, A. Taylor