By Dr. Michael Richie, MD Richie Eye Clinic – Faribault, MN
Remember when “food scientists” agreed that butter was bad for your health, artificial sweeteners were better for us than sugar, and vegetable oil was good for your heart? It seems that not all “science” is created equally and rash, all- or-nothing conclusions rarely stand the test of time…so does aspirin really cause macular degeneration (AMD)? Many mainstream media outlets are now spewing warnings that aspirin use will lead to blindness, but can you really believe what you hear? The study causing all the uproar comes from Drs Barbara and Ronald Klein, highly regarded retina specialists at the University of Wisconsin. This husband-wife team and their colleagues have spent decades observing the fine folks of Beaver Dam, Wisc., and these population studies have helped understand the natural course of devastating diseases like diabetic retinopathy and design effective treatments that have saved vision in literally millions of diabetics worldwide. So are the Kleins credible? Absolutely. Does aspirin cause macular degeneration? Not so fast. Dr Klein followed a lot of people (4926) for 20 years and noted that 10% (512) developed early AMD while only 2.4% (117) developed advanced AMD. Next, when looking at the incidence of mild AMD, she compared regular aspirin users (10 years or more) with non-aspirin users and found no difference. Finally, when looking at advanced AMD, the aspirin takers had a risk of 1.76% compared to 1.03% for non-users. Proof that aspirin causes AMD? Let’s look deeper. Multiple studies have shown regular aspirin usage reduces the risk of cardiovascular disease (CVD), as Dr Klein notes in her paper. People with higher cardiovascular risk factors or actual CVD would therefore be expected to take aspirin more regularly than those with lower risks or no CVD. Cardiovascular disease, however, is one of three primary risk factors for the development of AMD (along with nutritional and genetic factors).
Taking this train of thought one step further, those people with cardiovascular disease (or at greater risk for CVD) are also those at greatest risk for developing AMD…and they SHOULD be taking aspirin if they are getting proper treatment for CVD. So if we know these people are at greater risk for AMD, are we surprised they have a higher incidence that those without cardiovascular risk factors?
Herein lays the problem with scientific studies; to understand them you need to properly interpret them. Dr Klein performed an “observational” study: simply looking at things that happen to a population but not intervening to change anything or to test ideas. To best answer the aspirin question we would need to look at a large group of people with similar cardiovascular risks, then give half of them aspirin and the other half a pill they think is aspirin, but it really isn’t (a placebo). To avoid bias, neither the patients nor the doctors observing them can know who is which group and the data is evaluated by a third party (a double-blind study). In reality, prospective double blind studies are the gold standard in scientific research, but they are large, complex and expensive to carry out. More importantly, can we ethically withhold aspirin therapy from people who truly need it for their heart disease to decide if aspirin affects AMD? In this case, probably not. The practical explanation of Dr Klein’s observations is simple: most of the people taking aspirin regularly are also those most at risk for macular degeneration. Without a large prospective study involving thousands of people and lasting decades, we may never understand the link any better than that. The bottom line is this: if you do not have macular degeneration, taking aspirin is not a concern; if you need aspirin for your heart disease, take it. If you have both heart disease and macular degeneration, make certain you take the recommended eye vitamins, then weigh the advantages of aspirin therapy for your heart against the small chance that it can accelerate your AMD.
Does Aspirin Cause Macular Degeneration?