December 2008

 

GLAUCOMA

 

Fruits and vegetables impact glaucoma risk


by Vanessa Caceres EyeWorld Contributing Editor

   

Findings deserve further study, physicians say

Fruits and vegetables

A new study shows that eating certain fruits and vegetables more often may be associated with a lower risk of glaucoma for older women.

The study, which measured glaucoma with optic nerve head photographs and visual field testing in 1,155 women over age 65, found that the odds of a glaucoma diagnosis decreased 69% in women who ate at least one serving a month of green collards and kale compared with participants who ate less than one monthly serving. The risk of glaucoma was lowered by 64% in women who ate more than two servings a week of carrots compared with those who ate less than one serving a week. Glaucoma risk was lowered by 47% in women who consumed at least one weekly serving of canned or dried peaches compared with those who ate one serving or less a month.

Published in the June 2008 issue of the American Journal of Ophthalmology, the study was led by Anne L. Coleman, M.D., department of ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles.

The study adds interesting evidence to those who wonder whether a healthier diet may aid in lowering glaucoma risk.

Study details

Investigators analyzed glaucoma and its relation to fruit and vegetable consumption in a group of patients who had participated in the Study of Osteoporotic Fractures, a multicenter longitudinal cohort study that has been described in medical journals. Involvement in the study for surviving participants included a 10-year follow-up clinical examination, which 5,482 of the 9,704 original participants completed. During the eye examination, the volunteers had visual field testing in each eye with a 76-point suprathreshold visual field test. From that, 1,274 women were randomly selected for glaucoma photograph grading. Participants with suspected glaucoma had their optic nerve head photographs evaluated by two masked, trained glaucoma specialists who judged the appearance of the optic nerve head and the presence of visual field loss using results from the Humphrey Field Analyzer (Carl Zeiss Meditec, Dublin, Calif.). Participants tracked their fruit and vegetable consumption with a Food Frequency Questionnaire, which asked them how often they had eaten certain fruits and vegetables in the previous year. “The following items were analyzed in this study: canned or dried peaches, raw or cooked spinach, orange juice, green salad, fresh apples, bananas, oranges, green collards and kale, and carrots,” investigators wrote. “These items were chosen based on past research about the relationship between eye diseases and the intake of fruits and vegetables.”

Investigators also calculated the nutritional value of the fruits and vegetables that were studied, including antioxidants, fat, protein, carbohydrates, and nutrients.

Because of poor quality photographs or incomplete Food Frequency Questionnaires, the study pool was eventually reduced to 1,155 women, of whom 87.5% were white and 12.5% were black. The average participant age was 79.4 years, with an overall range of 67 to 97 years. Slightly over 8% of the participants were diagnosed with glaucoma in at least one eye, a prevalence that seemed to increase with age.

Measuring up fruits and vegetables

When investigators adjusted for study site, age, race or ethnicity, education, smoking status, alcohol consumption, walking for exercise, self-reported health status, presence of self-reported diabetes and hypertension, and presence of clinically diagnosed late age-related macular degeneration, they hit on some trends for an increased or decreased risk of glaucoma in certain patients.

Not only did they discover that women who ate a certain number of servings of carrots, fresh green collards or kale, and canned or dried peaches had a lower risk for glaucoma, they also found that the odds of having glaucoma increased by about 70% in patients who drank at least one serving of orange juice a day. Additionally, women who ate more than one weekly serving of spinach had greater odds of a glaucoma diagnosis compared with those who ate less than one serving a month.

When tracking the relationship between individual nutrients and glaucoma, investigators discovered that women who consumed at least 2 mg of vitamin B2 from natural food sources or at least 1,400 daily retinol equivalents of vitamin A were less likely to be diagnosed with glaucoma than participants who consumed lower amounts of these nutrients. At the same time, women who consumed 50 to 99 micrograms of cryptoxanthin had an increased risk for glaucoma compared with participants who consumed less than 50 micrograms of cryptoxanthin from food. Cryptoxanthin is a nutrient component found in orange juice.

Investigators were not sure why certain foods known to be healthy seemed to increase the risk for glaucoma while other foods with similar compounds decreased the risk.

“Constituents of fruits and vegetables, including flavonoids, isothiocyanates, fiber, and potassium, benefit the health of individuals. Antioxidants also may act synergistically with other constituents of food including components of fruits and vegetables,” they wrote.

The association between orange juice and spinach and the increased risk for glaucoma deserves further study, the investigators wrote.

Exploring nutrition angles

Although Dr. Coleman and co-investigators’ study does not provide definitive answers, glaucoma specialists believe it gives some evidence to use when patients ask about the connection between nutrition and glaucoma.

“Many ask if there is anything they can do to modify or reduce their risk of losing vision from glaucoma,” said Louis B. Cantor, M.D., Jay C. and Lucile L. Kahn Professor of Glaucoma Research and Education, Indiana University School of Medicine, Indianapolis. “We usually can say little but to use their drops, perhaps exercise, and perhaps take care of any chronic system disease such as diabetes and hypertension. However, many patients ask if diet has any impact, and we have had virtually no information to share with patients. Perhaps now we can begin having a conversation with patients regarding nutritional issues and glaucoma.”

Other recent studies have also examined the nutrition question as it relates to glaucoma. For example, a November 2007 Survey of Ophthalmology article discussed the roles of omega-3 fatty acids, cacao beans, gingko, green and black tea, and even coffee as stabilizing circulation, improving endothelium-dependent vasorelaxation, and serving a protective role against oxidative stress. A 2007 study published in Investigative Ophthalmology and Visual Science reported a 13% decrease in IOP at 40 weeks of age in rats fed an omega-3 sufficient diet. The fruits and vegetables study also calls into question how a certain combination of nutritional factors may decrease the odds of a glaucoma diagnosis. For example, collards and kale had a large effect on reducing glaucoma risk, but specific oils used in the cooking process or even herbs or other flavoring ingredients may have contributed to their beneficial effects, said Adrienne L. West, M.D., department of ophthalmology and visual sciences, W.K. Kellogg Eye Center, University of Michigan, Ann Arbor, Mich., who has previously studied nutrition and eye diseases.

“Interestingly, another vegetable that has a lot of similar vitamin content [as kale] is spinach, yet spinach actually showed a trend here to increase the risk of having glaucoma … perhaps it is not just a single vitamin that is protective or beneficial, but the combination present in these foods,” Dr. West said.

“Ultimately, there are likely going to be environmental and behavioral factors that contribute to the development of glaucoma in patients with particular genotypes,” said Douglas J. Rhee, M.D., assistant professor, Massachusetts Eye and Ear Institute, Harvard Medical School, Boston.

Editors’ note: Drs. Coleman, Cantor, West, and Rhee have no financial interests related to their comments.

Contact Information

Cantor: 317-274-8485, lcantor@rupui.edu

Coleman: colemana@ucla.edu

Rhee: 617-573-3670, DougRhee@aol.com

West: adrwest@umich.edu

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