1. In a secondary analysis of a large, randomized low-fat dietary modification trial in middle-aged women, there was no significant difference in primary open-angle glaucoma incidence between the low-fat diet and control groups.
2. Subjects within the dietary modification trial in the lowest quartile of fat consumption had significantly higher subsequent glaucoma risk compared to controls.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Glaucoma is a chronic disease and a common cause of blindness. Cardiovascular risk factors elevate risk for primary open-angle glaucoma, while dietary and lifestyle modifications like antioxidant intake may decrease risk and progression. This study aimed to conduct a secondary analysis of a dietary modification trial in women, for whom glaucoma is often underdiagnosed and undertreated, with the hypothesis that a low-fat diet would protect against glaucoma. Among about 23,000 women, there was no overall difference in rates of incident glaucoma between the group that undertook dietary modification and the control group. When participants in the dietary modification were stratified by percentage of calories obtained from fat, glaucoma risk was found to be significantly higher in the lowest-fat quartile. Interpretation of this study is limited by the fact that this was a secondary analysis based on Medicare claims data; neither prevalent nor incident glaucoma diagnoses were part of the prospective trial’s data collection. The mechanism of a possible deleterious effect of a very low-fat diet on glaucoma risk is not entirely clear, but it is plausible that a balanced diet with moderate fat intake and high antioxidant intake would best protect against glaucoma.
Relevant Reading: Risk factors and open-angle glaucoma: Classification and application
In-Depth [randomized controlled trial]: Prospective data were pulled from the Women’s Health Initiative trial, which included women aged 50-79 enrolled between 1993 and 1998. Medicare part B claims data from 1993-2018 was then linked to trial participants and used to determine glaucoma diagnosis based on ICD codes. Women with diagnosed glaucoma at baseline were excluded, but rates of undetected prevalent glaucoma were assumed to be similar between trial groups at trial onset. The dietary modification, continued for a mean of five years, involved a low-fat diet (20% of daily energy from fat) with at least five servings each of fruit and vegetables and six servings of grains per day. An intention-to-treat analysis was used to compare glaucoma incidence between groups, yielding an adjusted hazard ratio of 1.04 with a 95% confidence interval (CI) of 0.96-1.12. The hazard ratio was 1.22 for the quartile of the intervention group taking in the fewest calories from fat compared to the control group (95% CI 1.05-1.41, p = 0.007).
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