As the American population ages, it’s to be expected that medical conditions that typically affect older individuals will increase in incidence. Age-related macular degeneration (AMD) certainly fits this description: in the decade spanning 2000 – 2010, the number of people with AMD increased 18 percent, from 1.75 million to 2.07 million. This is projected to more than double by 2050, with over 5 million people potentially afflicted. Recent research out of Australia sheds light on why the macula is more susceptible to damage and degeneration than other parts of the retina.
Scientists have discovered differences in the shape and physiology of the same type of cell taken from different parts of the retina. These cells, called Müller cells, are the major glial cells of the retina. They’re present in the macula and also in the peripheral retina, and they have key roles in nerve cell function, metabolism, and activating light receptors in the eye. Müller cells are also believed to be the production site for the non-essential essential amino acids serine and glycine.
Owing to their critical functions, dysfunction of Müller cells may play a role in AMD and select other eye conditions, particularly macular telangiectasia. In examining Müller cells isolated from healthy donors, researchers noted distinct differences in the shape of cells from the macula and cells from the peripheral retina. The former were small and star-shaped while cells from the latter were larger and had multiple processes. Differences in expression of over 7000 genes were noted between cells from the two locations, including key genes involved in serine synthesis.
The enzyme phosphoglycerate dehydrogenase (PHGDH) is rate-limiting in serine synthesis, and it’s expressed more in macular Müller cells. Blocking PHGDH activity appeared to decrease retinal Müller cells’ ability to withstand stress. When the enzyme was blocked, the macular cells showed a higher degree of toxicity, potentially as a result of depletion of protective glutathione and a higher level of damaging reactive oxygen species compared to that observed in cells from the peripheral retina. Mark Gillies, one of the study authors and Professor of Clinical Ophthalmology and Eye Health at the University of Sydney, noted, “A better understanding of the unique biology of these cells could help to prevent and treat sight loss in future."
More research remains to be done, of course, but in the meantime, there may be a role for diet and lifestyle in treating or preventing AMD. Chris Knobbe, MD, gave an intriguing presentation at the 2018 Ancestral Health Symposium on whether AMD is preventable and treatable with an ancestral-style diet. Dr. Knobbe was co-author on a paper proposing that “the displacing foods of modern commerce” are a primary and proximate cause of AMD. (The phrase was coined by nutrition research pioneer Weston A. Price, DDS.) He noted that AMD was a “medical rarity worldwide” until approximately 1930, when it began rising modestly in prevalence, reaching epidemic proportions by the 1970s. It’s hard to ignore that this increase in incidence parallels those of type 2 diabetes, obesity, cardiovascular disease, and other issues known to have a significant basis in diet and lifestyle, and which were also rare until recently. It’s impossible to link individual food items with any one particular disease process, but evidence suggests that increased intake of refined sugar and industrial seed oils precedes the appearance of AMD within a population by about 30-40 years, and that it may take these nutritionally empty foods approximately that long to cause their damage over time.
Aside from avoiding refined sugars and isolated seed oils, another aspect of an ancestral-type diet that may be beneficial for those with AMD is increased intake of omega-3 fats. We covered the details in a past article on the role of fish oil in eye health and have also taken a look at research indicating fish oil supplementation may help lower risk for glaucoma and ocular hypertension. Previous articles have also explored other specific nutrients and phytochemicals that support eye health, such as tocotrienols, lutein, and astaxanthin.