Troy Brown, RN
July 23, 2018
People who consume at least one orange per day have a 60% lower risk of developing age-related macular degeneration (AMD) 15 years later compared with those who do not eat oranges, a study has found.
"[W]e report independent associations between dietary intakes of total flavonoids, and some of the common flavonoid classes (e.g., flavonols and flavanones), and AMD among older adults. Furthermore, the consumption of oranges and orange juice, one of the main foods and beverages contributing to total flavanone intake, is also likely to independently influence the risk of AMD," the authors write.
Bamini Gopinath, PhD, from the Center for Vision Research, Department of Ophthalmology and Westmead Institute for Medical Research, Australia, and colleagues published their findings online July 6 in the American Journal of Clinical Nutrition.
The researchers conducted a population-based cohort study of data from the Blue Mountains Eye Study. They included 2856 adults aged 49 years or older at baseline who provided dietary information for prevalence analyses, 2037 of whom were followed up 15 years later and were included in incidence analyses.
Gopinath said that most research until now has focused on the effects of common nutrients such as vitamins C, E, and A on eye health. "Our research is different because we focused on the relationship between flavonoids and macular degeneration. Flavonoids are powerful antioxidants found in almost all fruits and vegetables, and they have important anti-inflammatory benefits for the immune system," Gopinath explained in a news release.
The study used a semiquantitative food-frequency questionnaire to assess dietary intake, and the US Department of Agriculture Flavonoid, Isoflavone, and Proanthocyanidin databases to estimate the flavonoid content of foods in the food-frequency questionnaire.
The researchers first adjusted for age and sex, and then for covariates linked to the incidence of AMD in the Blue Mountains Eye Study cohort, including current smoking, fish consumption, intakes of lutein and zeaxanthin, and genetic variation.
For each one standard deviation (1-SD) increase in consumption of total flavonoid intake, a person's likelihood of any AMD was reduced by 24% (multivariable-adjusted odds ratio [OR], 0.76; 95% confidence interval [CI], 0.58 - 0.99).
The prevalence of any AMD was reduced by a similar amount for each 1-SD increase in intake of flavonols (multivariable-adjusted OR, 0.75; 95% CI, 0.58 - 0.97) and total flavanones (multivariable-adjusted OR, 0.77; 95% CI, 0.60 - 0.99).
Each 1-SD increase in consumption of quercetin (a flavonol) was also associated with lower odds of any AMD (OR, 0.76; 95% CI, 0.58 - 0.99).
When the researchers looked specifically at consumption of oranges, they found that people who consumed at least one serving of oranges per week but less than one serving per day had reduced likelihood of any AMD (multivariable-adjusted OR, 0.42; 95% CI, 0.21 - 0.84) when compared with individuals who ate no oranges.
The benefit was larger when advanced disease was considered, with a 92% lower risk for late AMD (OR, 0.08; 95% CI, 0.01 - 0.76).
"We examined common foods that contain flavonoids such as tea, apples, red wine and oranges," Gopinath said.
"Significantly, the data did not show a relationship between other food sources protecting the eyes against the disease."
Study strengths include prospective data collection, long follow-up duration, the use of a validated dietary tool, and adjustment for potential confounders. The researchers say the results apply to older adults in Australia, and possibly older adults in other Western countries.
"In addition, this study uses high-quality stereoscopic retinal photography with validated grading to assess macular conditions and a detailed side-by-side comparison of the baseline and follow-up photographs to ensure negligible misclassification of incident AMD," they add.
Study limitations include the fact that the study used US data only on flavonoid content of foods and that the results may not account for food variations in Australia. In addition, there may be "residual confounding from unmeasured or unaccounted factors (e.g., inflammatory markers) on observed associations," the authors write.
The study also may have been underpowered to detect modest associations between flavonoid intake and the development of incident AMD, as the number of participants who developed incident AMD was small.
"These findings suggest that a habitual diet high in flavonoids could play a role in AMD prevention and progression. These associations, if confirmed in other epidemiologic and intervention studies, could have important public health implications," the researchers conclude.
The authors have disclosed no relevant financial relationships.
Am J Clin Nutr. Published online July 6, 2018. Abstract