In the news: Flavonoid-Rich Diets & an Orange a Day May Help Keep AMD at Bay

Dietary Flavonoids and Risk of AMD

The majority of research to date has focused on the effects of antioxidants such as vitamins C, E, and A and the carotenoids lutein and zeaxanthin on AMD risk and progression. Increasingly, researchers are also exploring the potential role of phytochemicals with antioxidant and anti-inflammatory properties, including flavonoids – the bioactive compounds found in foods such as tea, chocolate, red wine, fruit, and vegetables.

There are 6 main classes of flavonoids: flavonols, flavan-3-ols, flavones, flavanones, anthocyanins, and isoflavones. In addition to the antioxidant and anti-inflammatory activities of flavonoids, there is strong evidence that they positively affect vascular health through improved endothelial function.

While flavonoids could act against AMD by minimizing oxidative stress and inflammation-associated damage and by improving vascular function, it is important to first establish whether intake of these phytochemicals is, indeed, beneficially associated with the risk of AMD.

To that end, a team of investigators from Australia conducted a population-based cohort study with a 15 year follow up to examine the relationship between dietary flavonoid intake and flavonoid classes, and the prevalence and 15-year incidence of AMD (1).

Notably, the researchers observed significant and protective associations between the intake of total flavonoids, as well as total flavonol and total flavanone intakes with AMD prevalence. They also observed more modest associations with several flavonoid classes, a key flavonoid and risk of incident late AMD.

Methods

Two thousand eight hundred fifty-six adults from the Blue Mountains Eye Study aged ≥49 years at baseline and 2037 participants followed up 15 years later, were included in prevalence and incidence analyses, respectively. Dietary intake was assessed by using a semiquantitative food-frequency questionnaire (FFQ). Estimates of the flavonoid content of foods in the FFQ
were assessed by using USDA Flavonoid databases. AMD was assessed by retinal photographs.

Results

Each 1 standard deviation increase in total overall flavonoid intake was associated with a 24% reduced likelihood of any AMD. (Multivariable-adjusted OR: 0.76; 95% CI: 0.58, 0.99).

Each 1 standard deviation increase in dietary intake of total flavonols and total flavanones was associated with 25% and 23% reduced odds, respectively, of the prevalence of any AMD. [Multivariable-adjusted OR (95% CI): 0.75 (0.58, 0.97) and 0.77 (0.60, 0.99), respectively].

A 61% reduced risk of late AMD after 15 years was observed in participants who reported consuming one or more servings of oranges per day compared with those who never consumed oranges at baseline. (Multivariable-adjusted OR: 0.39; 95% CI: 0.18, 0.85).

A marginally significant trend (P = 0.05) was observed between increasing the intake of total flavanone and the individual flavanone hesperidin (from the first to the fourth quartile), and reduced likelihood of incident late AMD, after multivariable adjustment.

Comments

These findings are plausible based on the biological activities of flavonoids reported in the published literature, and in line with existing evidence that adequate consumption of fruit and vegetables (abundant in flavonoids) is protective against AMD (2).

Consuming oranges and orange juice in particular (key contributors of flavanones in this cohort) was inversely and independently associated with both the prevalence and incidence of late AMD. Since there is a striking gap between the total flavonoid intake in this cohort (median 875 mg/day) and the total flavonoid intake in the US (median 117 mg/day), taking in more flavonoids daily should be a priority for those concerned about macular health. An orange a day may be a good way to start.

References

1. Gopinath B, et al. Dietary flavonoids and the prevalence and 15-y incidence of age-related macular degeneration. Am J Clin Nutr. 108:1–7, 2018.
2. Broadhead GK, et al. Dietary modification and supplement-ation for the treatment of age-related macular degeneration. Nutr Rev. 73:448–62, 2015.