Dietary nitrate and iron intake in a population at high-risk of primary open angle glaucoma

Abstract

Purpose : Africa has the highest rate of primary open angle glaucoma (POAG) in the world, often resulting in blindness. Dietary nitrate and iron intake have been associated with POAG risk in previous studies, which were all performed in European or American populations. We investigated these relationships in a high-risk population in Ghana, the country with the highest POAG prevalence in Africa, to explore if similar associations exist.

Methods : Consecutive patients visiting the eye clinic of the Komfo Anokye Teaching Hospital (KATH) were included in this study. POAG was classified according to the ISGEO criteria. Participants without POAG had to be at least 45 years of age, have an IOP < 21 mmHg, a vertical cup disc ratio (VCDR) < 0.5 and no family history of glaucoma. Dietary intake was determined using a semi-quantitative food frequency questionnaire (SFFQ), which was adapted to the Ghanaian diet. Food items high in nitrate were ranked based on their median nitrate content from literature. Dietary iron intake was calculated using the West African Food Composite Table by the Food and Agriculture Organization of the United Nations. Analyses were performed using multivariable logistic and linear regression while correcting for age, sex, educational level and total energy intake.

Results : We included 198 POAG cases and 281 unaffected controls in this study. Compared with the lowest quartile, the odds ratio (OR) for the highest quartile of nitrate consumption was 0.88 (95% CI, 0.51-1.52; P = 0.88). For iron consumption, the OR for the highest quartile compared to the lowest was 0.57 (95% CI, 0.22-1.42; P = 0.23). We did not find any associations with IOP.

Conclusions : Although a trend was visible, dietary nitrate and iron intake were not significantly associated with POAG or IOP. Aside from the relatively small sample size, a possible explanation may be that people of African descent have such a high a-priori risk for glaucoma that a relatively small effect of diet on glaucoma risk could not easily be detected.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.