Macular degeneration: Could eating grapes benefit eye health?

• A recent study found that a daily cup and a half of grapes may improve age-related vision problems.
• The findings suggest that daily grape consumption could improve a biomarker of macular degeneration in older adults.
• Grapes contain antioxidants that may reduce oxidative stress, which contributes to poor eye health.

Carrots aren’t the only food that’s good for eye health. A recent study found that a daily serving of grapes improved age-related vision problems in older adults.

The study is the first randomized, controlled human study of the potential benefits of grapes for human eyesight in the aging population.

According to the study’s authors, grape consumption reduces oxidative stress and benefits certain age-related biomarkers linked to macular degeneration.

Macular degeneration occurs in the eye’s macula, the central part of the retina, and generally occurs in people over 50. The condition makes it difficult for people to see things directly in front of them — although they can see things not centrally located.

The study results were recently published in the journal Food & Function. It was funded by the California Table Grape Commission, which played no role in its implementation, analysis, or interpretation of data.

Are grapes good for eye health?

The study involved 34 participants divided into two groups.

Over the course of 16 weeks, one group consumed the equivalent of 1.5 cups each day of table grapes in the form of freeze-dried table grape powder. (Using grape powder allowed for more precise portion control.)

The remaining individuals served as a control group, consuming a placebo powder instead.

Every four weeks, the researchers measured participants’ macular pigment optical density (MPOD) — lower density in the macula increases the risk of macular degeneration.

The researchers also observed how grapes impacted the accumulation of AGEs, an acronym for “advanced glycation end products,” measured in the skin.

At 16 weeks, the researchers observed a significant improvement in MPOD for the grapes-consuming group, and found that the control group had a significant increase in AGEs over the test period compared to the grapes-eating group.

Grapes help fight oxidative stress

Oxidative stress occurs when the body has an imbalance of free radicals and antioxidants.

A free radical molecule has an uneven number of electrons, and an antioxidant molecule can donate an electron to the free radical to remain stable.

Too many unstable free radicals can damage DNA, fatty tissue, and proteins, causing various problems throughout the body. One of these is macular degeneration.

The researchers measured participants’ total antioxidant capacity and overall phenolic content every eight weeks.

At the end of the study, the researchers observed an improvement in total antioxidant capacity and phenolic content compared to the control group.

One of the authors of the study, Dr. Jung Eun Kim, an assistant professor at the Department of Food Science & Technology at the National University of Singapore, explained to Medical News Today:

“Grapes are rich in antioxidants such as phenolic compounds (catechin, quercetin, resveratrol, and anthocyanin), certain carotenoids (lutein and β-carotene), and vitamins. These overall antioxidants may explain eye-protective effects against oxidative stress with grapes.”

How many grapes should you eat a day?

While there are no official guidelines on the number of grapes one should consume, Dr. Kim suggested, “From our study, we can say consuming 1.5 cups daily will benefit your eye health.”

However, consuming excessive amounts of whole grapes could spike blood sugar, especially in individuals with prediabetes and diabetes.

“It is important to remember that grapes, like many fruits, are high in natural sugars. It’s essential to consume grapes and other high-sugar fruits in moderation, especially if you have diabetes or are at risk of developing the condition,” Dr. Julia Giyaur, an ophthalmologist in New York who was not involved in the study, told MNT.

“It’s generally advisable to consume a balanced diet with a variety of fruits and vegetables to support overall eye health,” Dr. Giyuar added.

Other vegetables and fruits containing nutrients that support eye health include:

• carrots, sweet potatoes, and apricots — great sources of β-carotene
• spinach and kale — rich in carotenoid pigments, lutein, and zeaxanthin
• oranges — high in vitamin C

What are the mechanisms of age-related vision loss?

The current study indicates that grape consumption helped reduce the accumulation of “AGEs.”

Dr. Giyaur explained that AGEs “are a group of harmful compounds that form when sugars react with proteins or fats in the body through a process called ‘glycation,’”

Glycation may occur in the body from high sugar consumption or by eating foods cooked at high temperatures.

“[AGEs] are associated with various health issues, including inflammation, oxidative stress, and damage to tissues and cells causing aging and age-related conditions including macular degeneration, and play a role in diseases like diabetes,” Dr. Giyaur said.

Dr. Giyaur pointed out that of the study’s reported differences in AGEs over a 16-week trial, “the accumulation of AGEs in the body typically occurs gradually over many years.”

Therefore, detecting changes in AGEs levels after a brief study “might be challenging, as it may require specialized laboratory techniques and may not yield dramatic or easily observable results within that relatively short timeframe,” she noted.

More research on grapes for eye health needed

Could eating more grapes improve vision in people with macular degeneration? The answer is unclear.

Dr. Kim said this is a possibility but by no means guaranteed. She noted that the study shows an association between grapes and less macular degeneration but does not establish a cause for that association.

While the study measured MPOD as a biomarker of optical health, “other visual parameters were not accounted for, and this is a limitation of this work,” Dr. Kim said.

The researchers say they have received funding for a follow-up study next year in which they plan to measure more related parameters such as visual acuity, contrast/glare sensitivity, and photostress recovery time.

“We expect these visual parameters will be improved after grape consumption based on the current findings,” said Dr. Kim.

Dr. Giyaur expressed concerns regarding the small number of study participants, the short follow-up period, and the use of grape powder, which could have an even larger effect on blood glucose than whole grapes.

She said that prevention for age-related macular degeneration is “a complex issue influenced by multiple factors, including genetics, lifestyle, and overall diet.”

Nonetheless, Dr. Giyuar said the study raised valid points regarding the need for further research investigating the effect of diet on age-related diseases such as macular degeneration.

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