In the news: Carbohydrate Quality, Quantity Linked to Risk of Cataract

Meta-analysis: Carbohydrate Quantity & Quality Linked to Cataract Risk

Various risk factors including age, diabetes, smoking, UV-B light exposure and dietary intake of the B-vitamins have been reported to play important roles in cataract development. A number of studies have also investigated the possible association between carbohydrate nutrition and age-related cataract.

To evaluate this association, Zhejiang University researchers conducted a meta-analysis with results published in 2014 (1). The analysis, which included 7 studies (11,944 participants) of good methodological quality, used the random-effect model to calculate pooled ratios. The researchers also performed dose-response analyses, analyses based on cataract subtypes and assessed publication bias.

The authors looked at both the dietary glycemic index (GI) and the glycemic load (GL). The GI compares the potential of foods containing the same amount of carbohydrate to raise blood glucose, but it doesn’t take into account the amount of carbohydrate in the actual serving of a food. The GL incorporates both the quality and quantity of carbohydrates in the diet, and is a more accurate indicator of how a carbohydrate food will affect blood glucose.

Higher ‘carb’ intake (GL) and GI were significantly associated with an18% and 15% increased risk of age-related cataract, respectively, vs. lower intake. Sub-group analyses revealed a marginally significant association between higher carb intake and cortical cataract risk, and a significant association between greater GI and risk of nuclear cataract.

Additionally, a significant dose-response association was observed between intake of carbs and cortical cataract risk. No significant publication bias was detected.

The results indicate that higher quantity and lower quality (higher GI) of carbs may raise the risk of cortical and nuclear cataract, respectively. The authors call for more studies to further clarify these associations.

Positive Link: GL & Cataract Extraction Risk

The findings of a recently published study, not included in the meta-analysis, are consistent with the idea that a higher glycemic load is associated with developing age-related cataract. In this case-control study conducted in a Mediterranean population, Italian epidemiologists analyzed data from 761 cases of cataract extraction and 1,522 age and gender matched hospital controls (2). Multivariate odds ratios for GL and GI were obtained from logistic regression models, taking into account confounding factors including non-carbohydrate energy intake, smoking and diabetes.

A 57% higher odds of cataract extraction was seen when the top 1/3 and lowest 1/3 of GL were compared. A 20% non-significant trend was observed for GI in the same tertile comparison. Excluding those with diabetes from the analysis did not materially change the results. The cases and controls did not differ significantly across the categories of age, gender, education, smoking habits and body mass index.

Comments

The observed association between carbohydrate nutrition and lens opacities is biologically plausible. Metabolic studies have shown that a high intake of high GI carbs can cause a rapid glucose response after eating. Compared with many cells and tissues with a rapid uptake of glucose, the uptake of glucose from plasma into the aqueous humor and lens is relatively slow and the glucose is slowly turned over. This can lead to prolonged exposure of lens proteins to elevated glucose levels which could disrupt the polyol pathway, and lead to lipid peroxidation, cross-linking, and glycation – i.e. more oxidative stress.

View more information on low GL and GI foods

References

1. Han Wu, et al. Association between dietary carbohydrate intake and dietary glycemic index and risk of age-related cataract: A meta-analysis. IOVS 55:3660-68, 2014.
2. Turati F, et al. Dietary glycemic index, glycemic load and risk of age-related cataract extraction: a case-control study in Italy. E J Nutr 54:475-81, 2015.