Glycemic load and cataracts

Nutrition Research Newsletter, Oct, 2004

Different carbohydrates induce distinct plasma glucose responses, which can be quantified by the glycemic index. Dietary glycemic load is the product of the glycemic index of each particular food and its carbohydrate content, summed over all foods, and thus it represents the quantity and quality of carbohydrates in the overall diet and their interaction.

Age-related cataract remains the leading cause worldwide of blindness and visual impairment. Prevention or delay of this common condition would provide relief not only to those at risk but also by reducing the need for cataract surgery. Some evidence implicates hyperglycemia as a risk factor for the development of age-related cataract. If higher dietary glycemic load were related to cataract, modification of diets to lower the glycemic load might lead to a lower public health burden by reducing the incidence of cataract and the need for cataract extraction. The present study was undertaken to evaluate prospectively whether higher dietary glycemic load is associated with an increased incidence of age-related cataract.

Two cohorts, 71,919 women from the Nurses' Health Study (NHS) and 39,926 men from the Health Professionals Follow-up Study (HPFS), were used in this study. All the subjects were greater than 45 years and had no previous diagnosis of cataract, diabetes mellitus, or cancer. The women and men were followed for 14 and 12 years respectively, for the occurrence of cataract extraction. Dietary information was taken from a 126-item semi quantitative food-frequency questionnaire (SFFQ) in 1984 for women and 1986 for men. These dietary measurements were then repeated in 1986, 1990 and 1994 in the NHS cohort and in 1990 and 1994 in the HPFS cohort.

During 980,683 person-years of follow-up, 4,865 incident age-related cataract extractions were confirmed. After adjustment for age, cigarette smoking, BMI, total caloric intake, dietary intake of lutein and zeaxanthin, and alcohol consumption, there was no significant relation of dietary glycemic load to risk of cataract extraction.

In both men and women, the highest relative risk of cataract extraction, particularly for nuclear cataract, was in the second quintile of dietary glycemic load. Although the authors have doubts regarding the importance of this finding, given the overall null results, they were struck by the unusual consistency of this finding in the two separate large cohorts. However, the overall results show that a higher dietary glycemic load, which has been shown to induce hyperglycemia, is not a risk factor for cataract extraction.

Debra A Schaumberg, Simin Liu, Johanna M Seddon, et al., Dietary glycemic load and risk of age-related cataract, Am J Clin Nutr 80:489-495 (August 2004) [Reprints not available. Address correspondence to DA Schaumberg, Division of Preventive Medicine, 900 Commonwealth Avenue East, Boston, MA 02215. E-mail: dschaumberg@rics.bwh.harvard.edu]