Mediterranean diet may protect against macular degeneration

November 8, 2016
Laird Harrison

The Mediterranean diet reduces the risk of age-related macular degeneration (AMD), according to a study of two Portuguese populations.

The Mediterranean diet reduces the risk of age-related macular degeneration (AMD), according to a study of two Portuguese populations. 

The results from the Coimbra Eye Study, presented at the American Academy of Ophthalmology (AAO) 2016 annual meeting, also showed for the first time a correlation between lower AMD risk and increased caffeine consumption. However, the study did not determine whether caffeine in itself was beneficial or whether the benefits came from antioxidants, or some other ingredients, in coffee.

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The Mediterranean diet is the traditional preference of people living in many countries along the coasts of the Mediterranean and nearby. Compared to diets in most other western countries, it features a larger proportion of fruits, vegetables, whole grains, legumes and nuts, fish, poultry, olive oil, and red wine, and lower proportions of red meat, butter, and refined carbohydrates.

Lifestyle features other than these food groups are sometimes lumped into descriptions of the diet, such as exercising and eating in the company of family and friends.

Previous research has shown benefits to the diet in reducing the risk of a wide variety of illnesses, including heart disease and certain cancers, Parkinson’s and Alzheimer’s diseases, and in reducing overall mortality.

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At the same time, researchers have shown that specific minerals and antioxidants can slow the progression of AMD, including vitamin C, vitamin E, lutein, zeaxanthin, zinc, and copper.     

Researchers at the University of Coimbra, Portugal, and other nearby institutions decided to investigate whether the Mediterranean diet could reduce the risk of AMD.

They gathered data on 4370 people over the age of 55 years from the coastal town of Mira and 8692 from the inland town of Lousã. In an initial study, they found-after controlling for other factors-that those people living in Lousã had a prevalence of 15.39% for early AMD and 1.29%, for late AMD, compared with 6.99% for early AMD and 0.67% for late AMD in Mira, differences that were statistically significant (p<0.001).

Effects of diet

 

The overall prevalence of AMD in combined populations was 11.22%, slightly less than what has been reported in other large studies including the Beaver Dam Eye Study, which reported a prevalence of 14.1%, the EUREYE Study (12.60%), and the Visual Impairment Project (15.1%).  However, it was slightly greater than some other studies, including the Blue Mountains Eye Study (5.8%) and the Rotterdam Study (7.5%).

The Coimbra researchers wondered if people living along the coast might have different lifestyles affecting their risk of the disease. So they analysed records of diet for two sub-populations from their original survey, 449 with early AMD and 435 without early AMD from the two communities. 

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The two populations were similar in age, gender, education, body mass index, abdominal perimeter, and smoking status. However, there was a statistically significant difference in physical activity: the people with AMD exercised less than the people with AMD. Previous research has shown that exercise can reduce the risk of AMD.

The investigators created a scale from 0 to 9, awarding each participant 1 point for consumption above the sex-specific median of vegetables, legumes, fruits, cereals, fish, and monounsaturated lipids; consumption below the sex-specific median of red meat and dairy products; consumption of 10–50 grams per day of alcohol for men or 5–25 grams per day for women.

They found that 39.3% those who scored 6 or higher had early AMD, compared with 50.2% of those who scored below 6.

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Digging deeper into the data, they looked for differences in risk for each food group. They found that only consumption of fruit made a statistically significant difference; 54.5% of those without AMD ate less than 150 g a day, versus 45.5% of those with AMD (p=0.029). For reference, 150 g is about the weight of one apple.

The consumption of vegetables, legumes, fruits, cereals, and fish were all higher in people without AMD, and the ratio of monounsaturated lipids to saturated lips was higher in this group. But these differences were not independently statistically significant.

Role of caffine

 

Analysing micronutrients, the researchers found that fibre (both soluble and insoluble) consumption was significantly higher in people without AMD. So were beta-carotene, vitamin C, and vitamin E. And so was caffeine: in people without AMD, 54.4% consumed the equivalent of an espresso every day, compared with 45.1% of those with AMD (p=0.029)

Caffeine is not normally considered part of a Mediterranean diet, but coffee is popular in Lousã and Mira, one of the researchers told Medscape Medical News.  He speculated that the participants in the study might have benefited from the antioxidants in the beverage.

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The researchers found no statistically significant differences in consumption of omega-3 fatty acids, omega-6 fatty acids, zinc, or alcohol.

“High adhesion profile to the Mediterranean diet seems to be protective in AMD, which might be explained by increased consumption of fruits and some antioxidant micronutrients,” the researchers concluded.

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