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Dietary Glycemic Index (GI) and Early AMD
A previous EduFacts reported results from the first study ever to evaluate the relationship between the quality of carbohydrate intake and AMD. That study, which examined 526 women enrolled in the Nurses' Health Study, found that consuming a high Glycemic Index diet (dGI) was significantly associated with early signs of AMD. The glycemic index is a measure of how quickly carbo-hydrates are metabolized - the faster they are broken down into glucose, the higher the GI.
The same research group from Tuft's Research Center on Aging has now evaluated the dGI and AMD relationship among AREDS participants. Compared with the earlier investigation, the present study had older subjects, was much larger, offered a far greater number of AMD cases, and reflected a more complete spectrum of lesions that define AMD.
Lower GI Reduces Early and Late AMD Risk
The new findings are generally consistent with those of the previous study, finding a positive association between dGI and large drusen. They also report a 49% increased risk of advanced AMD (geographic atrophy plus neo-vascularization) for those with a dGI higher than the median for men and for women. According to the authors, 20% of prevalent AMD cases would have been eliminated if participants had consumed diets below those median values.
Study Design and Methods
Dietary information was obtained from 4099 non-diabetic participants aged 55-80 (56% women) in the ARED Study. A total of 8125 eligible eyes at baseline were classified into 1 of 5 AMD groups according to the size and extent of drusen, the presence of geographic atrophy, and neovascular changes. A generalized estimating approach was used to evaluate relationships between dGI and risk as well as severity of AMD, with eyes as the unit of analysis.
Higher the GI, the Greater the AMD Severity
When participants were split into 5 groups based on dGI, eyes in the 4th and 5th quintiles had a significantly or suggestively higher risk of large drusen, geographic atrophy and neo-vascularization compared to eyes in the 1st quintile. A significant positive relation between dGI and severity of AMD was also noted (P for trend 0.001). There was a 49% increase in the risk of advanced AMD for persons with a dGI higher than the sex median (women: >77.9; men: >79.3). The data show that the higher the dGI, the greater the severity of AMD (see Figure 1 below). FIGURE 1. Multivariate-adjusted mean dietary glycemic index (dGI) by age-related macular degeneration (AMD) groups. Error bars represent 95% confidence levels.
Importance of Limiting Simple Sugars
According to senior author Dr. Allen Taylor, simple sugars can modify proteins (creating advanced glycation end-products), cause oxidative stress that increases inflammation, and may damage vessels due to the sharp rise in blood lipids that can follow their consumption. This is important because there's been a trend of increasing carbohydrate intake (simple sugars found in cakes, cookies, sodas, white bread, etc) over the past 30 years. While long-term prospective trials are needed to confirm the adverse effects suggested by this study, a high dGI has already been implicated in the development of diabetes, CVD and some cancers.
Reference Chiu CJ et al. Association between dietary glycemic index and ARMD in non-diabetic participants in the Age-Related Eye Disease Study. Am J Clin Nutr 86:180-8, 2007.
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