According to new calculations published in the British Journal of Ophthalmology, an estimated 77 million Europeans will be affected by age-related macular degeneration (AMD) by the year 2050, with global estimates reaching 300 million by 2040. Like Europeans and other developed countries, AMD is the leading cause of irreversible vision loss and blindness in older Americans over the age of 65. When advanced, AMD can be treated, but not cured.
As we age, the macula－the light-sensing tissue at the back of the eye within the central portion of the retina that provides sharp and detailed central vision－deteriorates; and in advanced stages, blood vessels grow and leak fluid and blood into the macula obscuring vision. Because the macula is responsible for allowing us to see fine detail, when fluid and blood build up in that area of the eye, it causes severe damage and vision loss.
The Gut-Retina Axis
Although AMD is a complex disease that has yet to be fully understood, researchers have identified genes and pathways that are involved in the pathobiology of AMD, the most plausible target genes among them being B3GLCT and BLOC1S1. Dietary, lifestyle and environmental factors interact with these target disease genes that may contribute to the development of the disease and its severity; for example, smoking increases the risk of AMD, while increasing intake of dark, leafy greens and fatty fish reduces risk.
According to a review published in Nutrients, dysbiosis and/or leaky gut, chronic inflammation, aging, smoking, obesity, poor dietary habits, and UV-B light exposure influence the risk and progression of AMD. Our intestinal microbial ecosystem is largely driven by our diets; animal studies show that obese mice have 50% fewer Bacteroidetes and proportionally higher levels of Firmicutes compared to lean mice. The gut microbiome plays a pivotal role in determining the host’s metabolic pathways, in Western diets, for example, of obesity and low-grade inflammation (elevated production of IL-6, IL-1beta, TNF-alpha, and VEGF-A).
A high saturated fat, high refined sugar Western diet that mainly consists of dairy products, margarine, gravies, processed meats, sweets, and desserts, energy drinks, sodas, refined grains, and french fries was strongly associated with an increased predominance of advanced-stage AMD in a cross-sectional study. High fat diet-fed mice showed a 60% increase in neovascularization in retinal tissue compared to regular diet-fed mice, which may explain the role of the gut microbiome in retinal and choroidal neoangiogenesis, supporting the concept of a “gut-retina axis”. Furthermore, high-glucose and high-fructose fed-diets showed lower microbial diversity than normal diet-fed mice, and inflammatory cytokine expression was significantly higher in the colons of high-fat, high-glucose, and high-fructose fed mice than normal chow-fed mice, which increased lipopolysaccharide levels, altered intestinal permeability, and enhanced metabolic endotoxemia.
Nutrients to Support Vision and Eye Health
Because the eyes are constantly exposed to light-generated free radicals and other toxins which can cause major damage to the eyes, increasing the intake of eye-supportive nutrients may be beneficial for patients who are beginning to show signs of vision impairment as certain micronutrients have been shown to lower the risk of early-stage AMD progression. Lutein is a yellow carotenoid found in egg yolks, marigolds, kale, spinach, and broccoli that protects the retina from constant damage by free radicals. Like lutein, zeaxanthin is the other predominant fat-soluble antioxidant carotenoid that accumulates in the retina of the eye. Foods and supplements containing lutein (the esterified form providing superior absorption) and zeaxanthin (L/Z) can increase macular pigment density, which research shows is associated with prevention and/or slowing the progression of AMD. Among the 20 or 30 carotenoids present in human blood and tissue, L/Z are the only two found in the human eye.
In addition to lutein and zeaxanthin, the bilberry anthocyanins, as well as various other natural (not synthetic) mixed carotenoids, preformed vitamin A, vitamin C, vitamin E, zinc, alpha-lipoic acid, bioflavonoids, and polyphenols that are abundant in antioxidants are critical to maintaining optimal eye health. B vitamins from food and/or supplements are very important for modulating healthy levels of homocysteine. The amino acid, taurine, is another vital nutrient for vision and eye health; taurine and hypotaurine are known to be abundant in the young eye lens but have been shown to decrease by 70% in the aging lens.
Luckily for patients, aside from genetics, there are many modifiable and preventative factors for maintaining optimal eye health and visual acuity well into old age.