People who eat more green leafy vegetables such as kale, spinach and Swiss chard, good sources of nitrate, may significantly decrease their risk of developing glaucoma, say researchers from Brigham and Women’s Hospital and Harvard Medical School in Boston.
Based on long-term data for more than 100,000 U.S. adults, those who consumed the most nitrate – mostly from green vegetables – were 21 percent less likely than those who ate the least nitrate to develop open-angle glaucoma by the time they were in their 60s and 70s.
Open-angle glaucoma, which affects about 1 percent of the U.S. population, usually starts with loss of vision at the periphery due to fluid build-up and optic nerve damage.
Nitrate tied to improved blood flow
Impaired blood flow is implicated in the condition; nitrates can be converted in the body to nitric oxide, which improves blood flow. Nitric oxide may also be important for keeping eye pressure low.
The researchers used data on more than 63,000 women followed from 1984 to 2012 in the Nurses’ Health Study, and more than 41,000 men in the Health Professionals Follow-up Study from 1986 to 2012.
The participants were over age 40 at the beginning of the study period, had no open-angle glaucoma to start with, reported regular eye exams and completed dietary questionnaires including how often they ate green leafy vegetables like romaine lettuce, kale, mustard greens, chard or spinach.
The researchers then calculated intakes of nitrate and of various groups of foods. They found that dark leafy greens were the biggest source of the nutrient, contributing 57 percent of the nitrate in the participants’ diets.
The men and women were divided into five groups by their intake of greens and of nitrate, ranging from an average of one-third serving of leafy greens (80 milligrams nitrate) per day for the lowest-level consumers to an average one and a half servings of greens (240 milligrams nitrate) per day on the high end.
Both leafy greens and dietary nitrate protective
Risks for glaucoma based on nitrate consumption were very similar to those based on leafy-vegetable consumption.
People who ate the most leafy greens were 18 percent less likely than those who consumed the least greens to develop any form of open-angle glaucoma. 15 ways to add leafy greens to your diet.
People who consumed more nitrate also had higher consumption of other nutrients, exercised more, smoked less and were leaner, but the researchers adjusted for these factors.
Higher dietary nitrate intake has been linked to lower blood pressure, better blood circulation and better athletic performance.
But some people, like those with calcium oxalate kidney stones or those taking warfarin to prevent blood clots, need to avoid foods like spinach, kale and collard greens.
Glaucoma is a “silent” disease and usually does not cause symptoms or visual complaints until late in its development. African Americans and the elderly are at increased risk of glaucoma.
This is the first study to evaluate dietary nitrate in relation to glaucoma
Source: JAMA Ophthalmology, online January 14, 2016.
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