This article was first published in The Montreal Gazette.
Though most people have probably never heard the term, age-related macular degeneration, or AMD, it is the leading cause of adult blindness in developed countries. As the name implies, it is a degenerative condition that slowly robs people of their sight. The incidence increases sharply with age, affecting virtually no one under age 55, 0.2 percent of people over 65, and 13 percent of people over 85. AMD can be debilitating since the gradual vision loss often means patients cannot drive a car and are thus robbed of their mobility and independence. With our aging population, preventing AMD would be extremely useful.
Unfortunately, many proposed therapies for preventing AMD have not panned out when they are actually tested. Over the years, people have hypothesized that vitamin D and omega-3 fatty acids might help prevent AMD. However, both have been proposed as treatments for almost every medical condition under the sun, often with disappointing results.
In a paper recently published in JAMA Ophthalmology, researchers examined data from the VITAL study, which had previously shown that vitamin D and omega-3s were not effective at preventing cancer or heart disease. The study randomized over 25,000 people to receive either vitamin D, omega-3s, both or neither. After five years of follow-up, neither vitamin D nor omega-3s reduced the number of AMD cases compared to a placebo.
Over the years, other vitamins and supplements have been tried as well. A 2017 Cochrane review concluded that vitamin E actually slightly increased the risk of developing AMD rather than preventing it. The same review also showed that beta-carotene and vitamin C did not prevent AMD either, which was largely in keeping with an earlier 2007 study in the British Medical Journal.
These findings may be surprising to many people who have taken or seen ads for multi-vitamin supplements that claim to prevent vision loss. These claims are usually based on findings from the Age Related Eye Disease Study (AREDS). That study and its follow-up study, AREDS2, examined a multi-vitamin combination that included 500 mg of vitamin C, 400 units of vitamin E, 15 mg of beta-carotene, 80 mg of zinc oxide, and 2 mg of cupric oxide. Subsequent research found that beta-carotene increased the risk of lung cancer in smokers, and so the AREDS2 study was done in part to see if eliminating beta-carotene would make the medication less effective. Fortunately, it did not.
What often gets lost in translation is that the AREDS multivitamin formulation was quite effective at slowing the progression of AMD in patients who had moderate to severe disease. But contrary to popular belief, for patients with no AMD or with mild or borderline cases, there was no benefit.
It’s important to remember that there is an important distinction between treating a disease and preventing it. For example, antibiotics can treat pneumonia but are not terribly useful (with some exceptions) if your goal is to prevent pneumonia in the first place.
Since AMD is largely genetic in origin, there is probably not much that can be done to prevent it. There is some data to suggest that a Mediterranean diet and regular physical activity reduce the risk of AMD. And while this data comes from observational studies and not randomized trials, you should probably eat healthily and exercise anyway, given the multitude of other health benefits.
There is one thing that people can do to reduce the risk of AMD. Anyone wishing to prevent this very common cause of vision loss needs to quit smoking. Smoking is probably the most important modifiable risk factor, as smokers are two to four times more likely to get AMD than non-smokers. For people who wanted one more reason to quit smoking, this is it. Quitting smoking will very likely reduce the risk of vision loss due to AMD. Taking various vitamins and supplements probably won’t.