Dietary Nitrates From Green Leafy Vegetables Linked To Decreased Glaucoma Risk

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MedicalResearch.com Interview with:
Jae Hee Kang, MSc, SC
Associate Epidemiologist, Brigham and Women’s Hospital
Assistant Professor of Medicine, Harvard Medical School
Brigham and Women’s Hospital
Department of Medicine
Channing Division of Network Medicine
Boston, MA 02115

Medical Research: What is the background for this study? What are the main findings?

Dr. Kang: Glaucoma is a leading cause of irreversible blindness worldwide, and primary open-angle glaucoma (POAG) is the most common form of the disease. Little is known on the causes of glaucoma but dysfunction in the regulation of blood flow to the optic nerve, which transmits visual information to the brain, may be involved. Nitric oxide is important for maintenance of blood flow and its signaling may be impaired in glaucoma. We were interested in whether dietary nitrates, an exogenous source of nitric oxide mostly found in green-leafy vegetables, may be related to lower risk of POAG.

Medical Research: What is the background for this study? What are the main findings?

Dr. Kang: We (Brigham and Women’s Hospital / Harvard Medical School and Massachusetts Eye and Ear researchers) used 25+ years of data from over 100,000 participants in the Nurses’ Health Study (63,893 women) and the Health Professionals Follow-up Study (41,094 men). Participants were nurses or other health professionals and were aged 40 years or older and reported eye exams. We collected information on their diet and other health information every two years with questionnaires. During follow-up, 1,483 new cases of primary open-angle glaucoma with visual field loss were identified and confirmed with medical record review. Participants were divided into quintiles (one of five groups) of dietary nitrate intake (quintile 5, approximately 240 mg/day; quintile 1, approximately 80 mg/day) and of green leafy vegetables (quintile 5, approximately 1.5 servings/day; quintile 1, approximately one-third of a serving/day). We observed that greater intake of dietary nitrate and green leafy vegetables (e.g., romaine and iceberg lettuce and kale/chard/mustard greens) was associated with a 20 percent to 30 percent lower POAG risk; the association was particularly strong (40 percent-50 percent lower risk) for POAG with early paracentral visual field loss (a subtype of POAG most linked to dysfunction in blood flow autoregulation).

Medical Research: What should clinicians and patients take away from your report?

Dr. Kang: Because this was an observational study, it doesn’t prove cause-and-effect and thus, these results should be confirmed by other studies. It also does not provide data on whether nitrates may prevent further vision loss in those already with glaucoma. However, this study does add to the evidence for the role of nitric oxide in glaucoma. Furthermore, it underscores the public health message that greater vegetable intake may be important for maintaining eye health as well as overall general health.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Kang: Future research could explore the biological mechanisms of this relation by evaluating markers of nitrate in the blood in those with and without glaucoma and whether the relation with dietary nitrates may differ by genetic differences in nitric oxide signaling pathways.

Medical Research: Is there anything else you would like to add?

Dr. Kang: January is Glaucoma Awareness Month. With POAG, there are no symptoms and vision loss begins with peripheral vision, so glaucoma may go unnoticed until significant vision is lost. With glaucoma, when vision is lost, it is permanent. Therefore, the best way to protect against glaucoma is to get regular comprehensive eye examinations, especially for those aged 40 and older.

Citation:

Kang JH, Willett WC, Rosner BA, Buys E, Wiggs JL, Pasquale LR. 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 Ophthalmol. Published online January 14, 2016. doi:10.1001/jamaophthalmol.2015.5601.

Jae Hee Kang, MSc, SC (2015). Dietary Nitrates From Green Leafy Vegetables Linked To Decreased Glaucoma Risk 

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