As I’ve written before, macular degeneration is the leading cause of blindness in Australia, and 1 in 7 Australians over 50 suffer from it. Although the wet, aggressive, neovascular form is justifiably feared, there are pharmacological treatments widely available that for many patients salvage or restore vision. The dry, atrophic, form remains untreatable, and in some patients it inexorably progresses to its most advanced form, geographic atrophy (GA). In patients with GA there may be no functional macula tissue remaining, and central vision is lost.
Because dry AMD is untreatable, identifying and managing modifiable risk factors is very important. Avoiding exposure to cigarette smoke and increasing intake of fresh leafy green vegetables (high in lutein/zeaxanthin amongst other things) are well known strategies but a number of studies have also looked closely at the relationship between fatty acid (FA) intake and AMD. Total fat intake, saturated fat intake, trans-unsaturated FA intake and omega-6 FA intake have all been associated with increased risk of advanced AMD. This is particularly important because over the last several decades many people heeding well-intentioned health advice have attempted to reduce their saturated fat intake by replacing saturated fat in their diet with polyunsaturated vegetable oils (very high in omega-6 FA and now almost ubiquitous in processed foods) and their partially-hydrogenated derivatives which contain trans-fats.
A study in the current issue of Ophthalmology investigated the effect of dietary omega-3 FA on the progression of dry AMD to GA. The team, from Tufts University in Boston, found that increased intake of DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), the omega-3 FA found in fatty fish, was associated with reduced risk of progression, and reduced the effect of genetic susceptibility. They recommend that eating one or more 90g servings of fish high in omega-3 (eg salmon, herring, mackerel and sardines) may reduced the risk of progression.
The authors didn’t advocate omega-3 supplements. Rather, they suggested increasing fish intake. This is an distinction that is increasingly coming to be understood as important. Nutrients do not exist in isolation in nature, and don’t come traditionally to our diets readily labelled and understood. The traditional mediterranean diet, for example, is known to be high in both fresh leafy green vegetables, and olive oil. Although olive oil contains a high percentage of monounsaturated FA, it has been shown to increase the absorption of lutein from leafy green vegetables in laboratory rats. Making recommendations to patients for dietary change means thinking about more than isolated nutrients, or packaged supplements. It means considering diet as a whole, in the context of the whole person.
R Reynolds et al. Dietary omega-3 Fatty acids, other fat intake, genetic susceptibility, and progression to incident geographic atrophy. Ophthalmology. 2013 May;120(5):1020-8.
R Lakshminarayana et al. Lutein and zeaxanthin in leafy greens and their bioavailability: olive oil influences the absorption of dietary lutein and its accumulation in adult rats. J Agric Food Chem. 2007 Jul 25;55(15):6395-400.