Dietary Nitrate in Vegetables May Protect Against Glaucoma

Lara C. Pullen, PhD

January 15, 2016

Individuals who ate a diet higher in nitrate and green leafy vegetables had a lower risk for primary open-angle glaucoma (POAG). The protective effect was particularly noticeable for POAG with early paracentral visual field (VF) loss at diagnosis.

Jae H. Kang, ScD, from Brigham & Women's Hospital and Harvard Medical School in Boston, Massachusetts, and colleagues published the results of their analysis of data from the Nurses' Health Study online January 14 in JAMA Ophthalmology. They investigated the relationship between dietary nitrate intake (primarily from green leafy vegetables) and POAG.

The large prospective study included 1483 incident cases identified from 63,893 women and 41,094 men. The study was conducted from 1984 to 2012, and the investigators relied on questionnaires and medical records for disease confirmation.

The mean age for the 1483 cases of POAG was 66.8 years. Individuals who ate a diet high in nitrate and green leafy vegetables had a 21% lower risk for POAG. The reduction was found in the highest quintile of nitrate consumption (240 mg/day) relative to the lowest quintile of nitrate consumption (80 mg/day; relative risk [RR], 0.79; 95% confidence interval [CI], 0.66 - 0.93; P for trend = .02).

The association was even stronger for patients with early paracentral VF loss. This subtype of POAG is linked to dysfunction in blood flow autoregulation. Specifically, those in the highest quintile for consumption had a 44% reduction in risk compared with those in the lowest quintile (RR, 0.56; 95% CI 0.40 - .79; P for trend < .001).

Nitrates are naturally found in green leafy vegetables, as well as other vegetables, such as beets and carrots. Dietary nitrate is an exogenous source of nitric oxide (NO).

POAG appears to be the result of elevated intraocular pressure resulting from impaired autoregulation of optic nerve blood flow. Previous studies have suggested that the NO system plays a key role in POAG pathogenesis, with alterations in the NO system dysregulating ocular blood flow.

The authors explain that the nitrate–nitrite–NO pathway may thus represent an important alternative source of NO in patients with POAG, with one serving of green leafy vegetables making a significant contribution to the generation of NO.

"These results, if confirmed in observational and intervention studies, could have important public health implications," they write.

The authors have disclosed no relevant financial relationships.

JAMA Ophthalmol. Published online January 14, 2016. Full text

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