Leafy Greens (2016) Nitrate Content Helps Glaucoma
Nitric oxide has long been identified as a molecule which acts as a messenger within the central nervous system, which means that it delivers signals in the brain and through the optic nerve. In this capacity it helps to regulate the blood flow in the retina and the ability of the eye to regulate pressure within the vitreous humor through the outflow of the trabecular meshwork at the front of the eye.
We know that when the trabecular meshwork becomes blocked then outflow is blocked, intraocular pressure within the eyeball increases and the optic nerve is negatively affected.
So one obvious target in looking for treatments for high intraocular pressure is to take a closer look at the levels of nitric oxide in the body.
The very large Nurses' Health Study (nearly 64,000 women over 28 years) and the Health Professionals Follow-up Study (41,000 men over 26 years) has long been a source of data on various health conditions. Both studies include long-term assessement of participants' diets.
When looking specifically at glaucoma incidence the researchers identified that in almost 2 million person-years there were 1483 cases of primary open-angle glaucoma (POAG). The participants were classified by high intraocular pressure (lower than 22mmHg or higher than 22mmHg). They were also classified by what type of visual field loss existed (peripheral only or elsewhere in the visual field).
Then the participants were divided into 5 lowest to the highest nitrate rich diets. Comparing the lowest 1/5th group to the highest 1/5th group, the researchers found that they were much more likely to have developed POAG.
Visual field loss The higher levels of nitrate rich foods were more effective in protecting against early visual field loss in other parts of the visual field than the periphery (paracentral field loss).
Intraocular Pressure There was a similar difference between patients who'd had a higher level of nitrate rich foods in their diet and who tended to have more normal intraocular pressure, although not as great a difference as visual field loss protection.
Researchers: J. H. Kang, W. C. Willett, et al
Published: Association of Dietary Nitrate Intake With Primary Open-Angle Glaucoma: A Prospective Analysis From the Nurses' Health Study and Health Professionals Follow-up Study, JAMA Ophthalmology, March, 2016.
Editor's note: There's a great deal of discussion about nitrates which are added to meats as a preservative. Vegetables actually contain higher levels. We suspect that the beneficial effects of nitrates naturally taken in leafy greens are based on the relationship between those molecules and the other components, such as carotenoids, antioxidants, enzymes, vitamins and minerals, etc.