Age-related macular degeneration (AMD): can nutrition supplements slow its progression?

Age-related macular degeneration (AMD) is the leading cause of vision loss in people over the age of 50. AMD is a progressive disease seen as damage to the retina, which can lead to permanent central vision loss and even blindness. Good nutrition is important for eye health. And for many years, a range of nutrients have been specifically promoted as having a role in helping to protect the eye from AMD progression. Much of the evidence to support the role of nutrition in AMD has come from observational research. But there have been some long-term clinical trials using specific nutritional supplements that give a clue to what may work. In this podcast episode, I profile the results from a follow-up study to one of the biggest intervention studies in this area.

Links referred to in the podcast

• Nutrition supplements and AMD in the AREDS2 trial https://pubmed.ncbi.nlm.nih.gov/35653117

Episode transcript
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Transcript

Age-related macular degeneration (AMD) is the leading cause of vision loss in people over the age of 50. AMD is a progressive disease seen as damage to the retina, which can lead to permanent central vision loss and even blindness. Good nutrition is important for eye health. And for many years, a range of nutrients have been specifically promoted as having a role in helping to protect the eye from AMD progression. Much of the evidence to support the role of nutrition in AMD has come from observational research. But there have been some long-term clinical trials using specific nutritional supplements that give a clue to what may work. In this podcast, I profile the results from a follow-up study to one of the biggest intervention studies in this area.

Age-related macular degeneration (AMD) is a type of vision loss where there is a distortion or absence of the central field of vision. Peripheral or side vision is usually not affected. About one in seven Australians over the age of 50 show signs of AMD so it is an incredibly common condition.

Symptoms of AMD may include problems with close reading, distorted or blurred central vision, blank or dark spots and even complete loss of central vision.

The underlying cause of AMD is damage to the macula. The macula is the part of the retina that has the highest concentration of photoreceptor cells. In the early stages of AMD, there can be changes seen in the macula, but eyesight is usually unaffected. As it progresses to an intermediate stage, retinal damage increases and some blurring of vision is common. In the final late stages of AMD, there is enough damage happening to the retina that central blindness and other visual problems occur.

There is a range of risk factors for AMD which include age, family history, smoking and high blood pressure. Diet is also considered to have a role. And here, it is more about the presence of certain nutrients that are thought to have a role in vision and protecting the eye from damage. Some of these nutrients that have attracted attention include lutein, zeaxanthin, omega-3 fatty acids, zinc and beta-carotene.

So, a bit more about these compounds. First, there is lutein and zeaxanthin which belong to the vitamin A carotenoid family and are the main dietary carotenoids found in the human retina. They give fruits and vegetables a yellow to reddish hue although green leafy vegetables like kale and spinach are very good sources of it too, but the green chlorophyll colour masks the pigment colour. These compounds are thought to be present in the retina to help protect it. First, by acting as antioxidants to mop up free radicals, but also by absorbing blue light. People who have diets high in lutein and zeaxanthin appear to show a lower risk of late AMD. It is why popular supplements targeted at ‘eye health’ usually contain these compounds.

Then there are omega-3 fatty acids which are mostly found in seafood. The long-chain omega-3 fatty acids are important in eye health in part because the photoreceptor cells of the retina are rich in omega-3 fatty acids. Again, observational studies point to a lower risk of AMD in people with diets high in omega-3s. But observational studies are very different to clinical trials.

Then we have zinc. And the story continues that again observational studies show at least that a diet higher in zinc is linked to a lower risk of AMD, but not all studies show this. Interestingly, there has been one clinical trial that found that zinc supplementation, at a dose of 80 milligrams per day, seemed to lower the risk of progression to late AMD.

And finally, there is beta-carotene. Because everyone knows that carrots are good for your eyesight right? Beta-carotene gives the orange colour to carrots, pumpkin, and sweet potatoes, but you’ll also find it in leafy green vegetables too. Beta-carotene’s antioxidant ability could be an important mechanism to give some level of protection to the eye.

Just a quick random side track about carrots being good for your eyes in general. And well, of course, there is truth to this as loss of night vision is one of the first clinical signs of vitamin A deficiency which if left unchecked, can progress to irreversible blindness. But that doesn’t mean the more carrots you eat, the better your eyesight will be. Where a lot of this advice came from was way back in World War II when the British, as a way to hide the fact that they had developed radar and this was giving them an edge in intercepting and shooting down German planes, spread the propaganda that they were feeding their pilots lots of carrots to improve their eyesight and this was the reason. Now, I always thought this was a nice story that was plausible, but likely a myth, until one day I was doing a radio talkback segment on nutrition myths and this one came up. And low-and-behold an elderly gentleman called up and said he was actually based at a RAF fighter base in England during the war and they were fed lots of carrots in the mess hall for this very reason. I’m calling this myth: confirmed.

Okay, back to the topic of the day now that your theory is done. And onto the clinical trial that aimed to see if a combination of these eye nutrients could reduce the risk of progression to late-stage AMD. Firstly, the clinical trial has already been done and published some years ago. In fact, here we are talking about two related trials called the Age-Related Eye Disease Study (AREDS) and the Age-Related Eye Disease Study 2 (AREDS2). I won’t go into all the details of these studies as what I’m concerned with in this podcast is a follow-up study to the 5-year randomised controlled trial that was AREDS2. It examined whether various supplements could prevent the progression of intermediate AMD to late AMD. Older adults (with an average age of 72) with intermediate AMD were assigned to a number of intervention combinations.

During the clinical trial, participants were randomly assigned primarily to take lutein and zeaxanthin together with omega-3 fatty acids, or omega-3 fatty acids alone or a placebo. Then there was a second level of randomisation that some of the participants underwent where they were randomly allocated to take beta carotene or a placebo along with a low or high dose of zinc. A lot was going on here as it meant there were 16 different and distinct groups to compare.

At the end of the initial 5-year clinical trial, the participants were followed up every 6 months for another 5 years. This was the observational part of the study which was done to assess progression to late AMD as well as the incidence of lung cancer. I’ll speak shortly about why they were interested in lung cancer.

The results

So, let’s get into the results. The combination of lutein plus zeaxanthin, the two nutrients that have the closest link to eye health, reduced the risk of progression to late-stage AMD by 9 percent compared to people who didn’t take them, but may have taken some other nutrients. But when you compared the combination of lutein and zeaxanthin just to people who only took a placebo, the risk of AMD fell by 12 percent.

It was a bust though for the other supplements of omega-3s, zinc and beta-carotene in showing any benefit in a reduction in the risk of progression to late AMD.

Now onto why they looked at lung cancer outcomes too. Of the initially enrolled participants, 2.7 percent developed lung cancer at some stage. But this risk of lung cancer was higher in people taking the beta-carotene. This is not the first time this has been seen as several studies have found links between beta-carotene supplementation and the risk of lung cancer. Smokers and former smokers are the clear stand-out group for showing this higher risk. Health bodies for some years have warned people, especially smokers or former smokers, to not take beta-carotene and the results from this latest study support that advice. Why it could be harmful is unclear, but one idea is that this potent antioxidant can turn into a pro-oxidant at high levels due to the pressure in the lungs. It also could be related to a genetic risk that beta-carotene exacerbates. Importantly, none of the other nutrients taken in the study, especially the related compounds of lutein and zeaxanthin, were linked to a higher risk of lung cancer.

So, let’s wrap all this up and put these results into context. The finding of a clear benefit of lutein and zeaxanthin in lowering the risk of developing late-stage AMD is supported by prior research – adding to the reliability of the results. And it also validates why these nutrients are common additions to many supplements promoted for ‘eye health’.

With AMD such a common condition in the older population, and with longer lives meaning more people will progress from early to late AMD, the use of nutritional interventions that can slow this process will have a big benefit. For people at higher risk of AMD, then lutein and zeaxanthin are certainly supplements to consider. But then again, let’s look at the foods that are high in them like kale, spinach, and broccoli, but you can also add egg yolks, corn and pistachios to the list. All good healthy foods to have more of in your diet for your health, and your eyes.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.