Diet Soda, Dementia & Forever Chemicals: What the Research Really Shows

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Announcer 0:00

Welcome to MedEvidence, where we help you navigate the truth behind medical research with unbiased, evidence-proven facts, hosted by cardiologist and top medical researcher, Dr. Michael Koren.

Dr. Michael Koren 0:11

Hello, I'm Dr. Michael Koren, the executive editor of MedEvidence. And I have a terrific guest today who I think you'll really, really enjoy. Her name is Dr. Hannah Gardener. She's an epidemiologist and an associate professor at the University of Miami. Hannah, welcome to MedEvidence. I am super excited to talk to you about some of your incredible research. And you actually have a little bit of worldwide fame because of some of your findings about diet soda that we're going to get to in short order. So why don't you just start by introducing yourself to our audience? Tell us a little bit about your background and your current position and your passion.

Dr. Hannah Gardener 0:50

Sure. Thank you so much for having me today. So, as you mentioned, I'm an epidemiologist. In 2007, I got my doctoral degree in epidemiology from the Harvard School of Public Health. And from there, I moved to Miami, to the University of Miami Medical School, where I have been ever since for 19 years now. And my position is in the Department of Neurology. So I call myself a neuroepidemiologist because most of my work focuses on the epidemiology of vascular neurological outcomes, primarily stroke and dementia, but also subclinical vascular disease in the brain as well. And so I've been doing that for 19 years. And for the past 15 years, I have had sort of a side passion project or company called A-Green Slate, where I help families and organizations identify and reduce their exposure to common environmental toxins that everyone has in their homes, in their offices, in their environments, and identify ways to reduce exposure in an evidence-based, non-stressful or minimally stressful manner.

Dr. Michael Koren 2:11

That's great.

How Pregnancy Sparked Toxin Awareness

Dr. Michael Koren 2:12

Well, that's it's really exciting. So what triggered your passion about doing epidemiological work on these type of exposures? You know, it's scary when you think about it when you start to talk about these common exposures and how they may impact our health over time. So, how'd you get into it? Give us a little bit of insight into that.

Dr. Hannah Gardener 2:32

Yeah. So there were sort of two pathways. I think I've I've always been interested in the brain. In my undergraduate work at Dartmouth College, I was in the Department of Psychological and Brain Sciences. I was really passionate about neuroscience as an undergrad. I had no idea what the word epidemiology was or what an epidemiologist did until about a few years after college. And I met someone who was about to go to grad school in epidemiology. And I said, What's what's that? And when he described what it is, studying the causes and distribution of disease, it sounded like the perfect career for me for someone who I love math, I love statistics and health and sort of the marriage of those skills really is what epidemiology is. And so I naturally, from the start at Harvard, I was most interested in neurological psychiatric diseases. And my passion for environmental health and interest in environmental toxins happened when it does for a lot of women, I think, when I became pregnant. So I actually did my doctoral dissertation at Harvard was all about how prenatal risk factors impact neurological diseases. So I studied Parkinson's disease, MS, and autism. But why really, when I got to Harvard, what I said to my advisors is I really want to study prenatal risk factors for Alzheimer's disease. And everyone sort of looked at me like that was a crazy idea. You know, the the time span from the prenatal period to the development uh of Alzheimer's disease is so many decades, you know, that's probably not really relevant. Our thinking since then has changed about the importance of the prenatal environment for long-term brain health and our fear, our our knowledge about how how long before the clinical diagnosis of Alzheimer's that the uh the changes are actually happening. So I wasn't able to study that. There was also there, and there still isn't really great data because of, you know, just sort of the nature of epidemiology. If you're studying prenatal risk factors for outcomes that occur, you know, 60 years, 70, 80 years later, it's really hard to collect that data in a rigorous manner. So I have been interested in sort of early life, how the early life exposures impact long-term health really for my whole career. But it wasn't until I became pregnant with my first child in 2008 that I really started thinking about it on a more personal and critical way. And so suddenly all the topics that I had heard about in environmental epidemiology years before started, you know, flooding back to my brain. And I had was like, all right, you know, we were talking about these chemicals called phthalates. What are they? Where are they found? How can I avoid them? How can I avoid contaminants in food and in my home and in all the products that I'm buying for the child I'm about to have? And I really just like a sponge, I just started absorbing all of this information in a whole new way because suddenly it was impacting me and my future children. So I started to become really, really passionate about it. At that time, I was in both the pediatrics department and the neurology department, and I realized that there was sort of a significant lack of awareness in the medical school community about environmental toxins and how they impact health. I will say that over the past, so, so that was like 17 and a half years ago now, and over the past 17 years, the amount of knowledge and legitimacy that environmental toxins has had in the medical community has just skyrocketed. 17 years ago, I was sort of, you know, the kooky person who would throw out letters BPA and PFAS and there there wasn't the acknowledgement that these were real important exposures until probably maybe like the past decade.

Dr. Michael Koren 7:14

Wow. So I have so many questions for you. Just one thing I can't help but mentioning, though, is that how when I speak with guests, I never know what paths may have crossed between your career and my career. But it turns out that my first major clinical research endeavor was at the Harvard School of Public Health, and it actually involved uh perinatology. So I my thesis when I was at Harvard was about preventing the acid aspiration syndrome during surgery, including childbirth. And my first presentation was at the Society of Obstetrics and Perinatal Anesthesiology. So it's kind of funny how paths cross. But getting back to you, so I'm real curious. Well, first of all, how many kids do you have? How many pregnancies have you had?

Dr. Hannah Gardener 8:01

I have two children.

Dr. Michael Koren 8:03

Two children.

Dr. Hannah Gardener 8:03

Yep.

Dr. Michael Koren 8:04

And so what behaviors did you change personally to protect your kids against Alzheimer's and other problems?

Dr. Hannah Gardener 8:12

Yeah.

Practical Changes For Lower Exposure

Dr. Hannah Gardener 8:13

So during my first pregnancy, it was like an overhaul every day. You know, before being pregnant, I wasn't really that focused on eating organic foods or choosing organic foods. And so I started paying more attention to choosing organic foods in an effort to reduce exposure to pesticides. I stopped doing things like going to the dry cleaner, you know, dry cleaning my clothes. I started paying a lot more attention to reducing my exposure to plastic. I started being much more careful about the personal care products that I was using. And one of the big things that I started doing was just really thinking about anything that I put in and on my body, do I need it? You know, it's nice to, you know, wear nice smelling lotions and all sorts of fragrance products. But I quickly learned that those sort of products contain chemicals like phthalates and that it that are harmful for fetal development. And those are not listed on the ingredient labels. So I started being much more conscious of thinking about the products that I use and whether I really needed them or not. Because one of the best ways to reduce our exposure to toxic chemicals is just to put less products in and on our bodies.

Dr. Michael Koren 9:45

Interesting. And um there any, I out of curiosity, were there any products that you increased your consumption of during your pregnancies for the health of yourself or your children?

Dr. Hannah Gardener 9:56

Water consumption. I worked really hard to, you know, to increase water consumption and focus on hydration and consuming more fruits and vegetables and nuts and legumes. And at the time I was starting to do a lot of research into the Mediterranean style diet. And of course, I wasn't looking at that in relation to pregnancy, but the more I read, the more I understood that that is really the dietary style that has so much great evidence for health protection. And so I started thinking about the importance adhering more to that style of diet during pregnancy.

Dr. Michael Koren 10:33

So do you you ate more, you ate more fish or olive oil or hummus or what was it?

Dr. Hannah Gardener 10:39

Yep, mostly fruits and I paid much more attention to increasing my consumption of fruits and vegetables and nuts and legumes. During pregnancy, you have to be really careful about the fish you eat, and you know, not too much, not too little. So I started paying a lot more attention to that as well, and decreasing my consumption of processed foods as well. I don't think at the time we had the term ultra-processed foods, or at least it wasn't, you know, big in the medical community at that time, but I started thinking more about eating whole foods and less processed foods. At the time, I was also starting to do my research on diet soda. And so I was never a big consumer of diet soda, but I, you know, I probably stopped drinking it other than, you know, a few times a year during during that period as well. That's when I really started getting into the research on on diet soda accidentally. But in terms of products, I can't think of anything, any products that I necessarily increased my use of.

Dr. Michael Koren 11:51

All right.

Diet Soda Research And Surprising Signals

Dr. Michael Koren 11:52

So let's turn our attention to diet sodas since you bring that up. And I know that you have published some work in this area and maybe some concerns about consumption of diet soda, especially at high levels and adverse health outcomes, including dementia. So walk us through some of your research in this area.

Dr. Hannah Gardener 12:11

Yeah, so I got into the research on diet soda accidentally. A medical student or medical resident came to me and said she was really interested in the association between diet soda and strokes and heart attacks and vascular-related death. And I looked at her like she was crazy. I was like, I do you mean regular soda? You want me to, you know, let's take a look at regular soda? And she was like, I think we should look at at diet soda. And as many medical residents do who come with to me with research ideas, she got really busy and sort of fell out of my uh

Dr. Michael Koren 12:49

dump the work on you.

Dr. Hannah Gardener 12:51

Yeah, but I had already started looking at the data, and I was surprised at how strong the association was that I was seeing between diet soda being associated with an increased risk of strokes and heart attacks and vascular-related deaths. In particular, we're real where I'm talking about frequent diet soda consumption, like daily.

Dr. Michael Koren 13:16

So define that. Is that one diet soda a day? Is it five or six diet sodas a day? Give us a little bit of flavor. And also, are these any sodas that substitute sugar with something else? Is that how you define diet soda? Just guess into a little bit of the details.

Dr. Hannah Gardener 13:32

Yeah. So we don't actually define diet soda. And I should be clear, you know, we're using data that was collected between 1993 and 2001 in a large prospective cohort study that I work on called the Northern Manhattan Study. So the Northern Manhattan Study was initiated and the participants were recruited between 1993 and 2001, about 3,300 participants in total. And they have been followed through 2023. So we continue to follow these participants. And at their baseline recruitment, we gave them a really extensive diet questionnaire. I think there are 207 different items on that diet questionnaire. And one of those, one of the items was the frequency and amount of diet soft drinks that they consumed. And they we didn't sort of instruct them on, you know, how to define that. So there's a bit of ambiguity. They they could interpret that as they as they liked. I was in middle school at the time, so I certainly wasn't involved in that research, but that's when the data was collected. And I started working on the Northern Manhattan study in 2007, and that's sort of where I came into the picture with my own interests. And so we have data on what we looked at is the frequency with which people reported consuming diet sodas in between 1993 and 2001, and then their risk afterwards of having a stroke or a heart attack. We've looked at other outcomes as well. Most recently, I've published on their association with cognitive impairment and dementia. And what we saw is that the people who reported daily consumption of diet soft drinks, most of those people were consuming one per day, but some people were consuming much more because of the need for statistical rigor, we had to group those people together in most of our research. Although we have also sort of looked at the incremental increase in consumption of diet soda per day as well. And basically what we were very surprised to see was that not only does regular soda consumption increase the risk of these vascular outcomes, but increased consumption of diet soda does as well. Even when we take into account the the things anyone would think about. Oh, you know, it's because people who might be consuming diet soda are doing so in an effort to lose weight or to control their blood sugar, or it's because they already have a high risk of these vascular outcomes. And so they may switch to drinking diet soda from regular soda, or maybe they started drinking diet soda when they when they hadn't been consuming any soda before in an effort to sort of satisfy that desire for sweetness without without consuming calories. It makes sense. It's what I would have assumed at the time as well. What we now see is the consumption of these artificial sweeteners may actually be riskier for vascular disease than we had originally anticipated. And I, you know, I think it I want to be very clear. I don't think anyone should get the message that they should stop drinking diet soda and switch to regular soda. I mean, the amount of evidence that we have about the harms of regular soda are, you know, are really substantial. But what the evidence has started to show to show is that diet soda may not be innocuous either. And so reducing consumption and switching more to water and to tea and to coffee, the all of which have really great cardiovascular and cerebrovascular benefits is what is what makes sense. So I sort of had my 15 minutes of fame as an epidemiologist starting around 2011 when I first presented these results. And people were very skeptical. I was very skeptical. And since then, there has been a lot more evidence has come out, which has been consistent with what we showed originally that people who consume more diet sodas tend to have an increased risk of these vascular outcomes in the future.

Dr. Michael Koren 18:11

Interesting. So just to break down some of that amazing stuff. Well, thank you for sharing that. As I recall, I read the number of a 34% increase in dementia. Is that an accurate number and help us understand that number a little bit better?

Dr. Hannah Gardener 18:30

From my recent research?

Dr. Michael Koren 18:31

Yes.

Dr. Hannah Gardener 18:32

Yeah. So for that, we actually we categorize people as consuming more than one diet soda per day versus versus less than that. And we showed the people who consumed more than one diet soda per day, I don't remember the exact estimate off the top of my head, but it's in that ballpark, they had an increased risk of later developing later developing dementia. Now, in this study, what we found is that when we just focused on people who did not have diabetes and were not obese at baseline, that association in that study actually went away. In our other study, where we were focusing on stroke and heart attacks, it did not go away. So what I believe is that there is confounding and probably some mediation as well by obesity and diabetes. That there, what we also shown in the Northern Manhattan study is that people who consume more diet soda are at an increased risk of developing diabetes. So people who didn't have diabetes at baseline and consume more diet, more diet soda were more likely to develop diabetes over time. Other research, we haven't looked at this, but other research has shown that increased consumption of diet soda increases weight gain. But it's it's tricky to disentangle all these facts because also people tend to switch to drinking diet soda in an effort to lose weight and control their blood sugar. So it's really, it's really

What Prospective Data Really Means

Dr. Hannah Gardener 20:10

complicated.

Dr. Michael Koren 20:10

Yeah, a lot of a lot of intricate threads there. Does the sugar reduce your appetite for other calories and a bunch of other interesting things? Now you used the word prospective when you started talking about this study. And just for people that aren't familiar with those terms, that means typically that the questions you're going to ask the database were determined beforehand. And when the study was set up, all these things were thought out of ahead. But was actually diet sut one of those prospective elements, or was that a retrospective element of a prospective study?

Dr. Hannah Gardener 20:45

So when we talk about what's prospective, the key is that the exposures are asked about before the outcome has occurred. So we want to make sure that our temporality is correct, that it's not like we have people who, you know, who have stroke or we have people who have dementia, and we're asking them about what kind of sodas they drank in the past because a lot of epidemiological studies are conducted that way. And the problem is that people are not always accurate in their reporting of what they eat and what they drink. And they tend to be even more inaccurate once they've already had an outcome. And maybe they're trying to think about why they had that outcome. I mean, we know inherently it's problematic if you're asking people with dementia what you know what they ate in the past because dementia, you know, it comes with the main symptom is is memory problems. So, but with any condition, people will tend to either overestimate or underestimate an exposure if they think that it actually is tied to the outcome of interest.

Dr. Michael Koren 21:58

Gotcha. Yep. So it sounds like All the data were collected in a prospective manner, but questions could be asked to the database afterwards based on that prospectively gathered information.

Dr. Hannah Gardener 22:11

Exactly. You know, like I mentioned, I was in middle school or and in and in high school and then in college from 1993 to 2001 when all this data was collected. So from my perspective, if we defined what a prospective or retrospective study was based on that, every every piece of research I have, you know, done in northern Manhattan for the past 19 years would be considered retrospective. But where really where these terms really matter is communicating to people that we have our temporality correct, that the the data on the diet and beverage consumption preceded the outcome. And so as a result, what we do is we exclude people who've already had a stroke or already had a heart attack at baseline or they already have dementia. So that we're just looking at the association between diet, beverage consumption, and their future risk for an outcome.

Dr. Michael Koren 23:09

Got it. And that's very helpful. Thank you.

PFAS Forever Chemicals Explained

Dr. Michael Koren 23:12

So switching gears a little bit, you used the term PFAS earlier in our conversation. I know that you have some passion around that. So why don't you explain to everybody what those initials mean and why they should know about it?

Dr. Hannah Gardener 23:25

Yeah. So PFAS, we call that PFAS. It stands for PER and polyfloral alkyl substances. And that's a real mouthful, and that's why you never hear that long name in the media. The media likes to call these chemicals forever chemicals. Sometimes people call them everywhere chemicals. And those names are justified because PFAS are truly everywhere. And we call them for emic forever chemicals because they don't break down. They bioaccumulate in our bodies and they don't break down in the environment. So what are PFAS? PFAS are a very broad class of chemicals. There's over 10,000 of them actually. And they have been added to products for over 70 years. I think starting in the 1950s, they've been added to products to make them stain resistant, oil resistant, stick resistant, waterproof. So they are in our nonstick cookware. They are in our raincoats and snow gear to make them waterproof. They're in our workout gear to make them moisture wicking. They are in all of our furniture to make them stain resistant, our carpet, our rugs, the upholstery in our cars. They they're in our sticky notes. They're in our contact lenses. They are truly in our pizza boxes. A lot of um food packaging contains PFAS in the microwave popcorn bags. And they are also in our food. So they're substantial contaminants in fish, for example, because what happens is they do not break down in the environment. So they they contaminate pretty much every waterway and soil across the world. And as a result, every essentially every single human and animal in the world, our blood is contaminated now with PFAS. You know, you measured blood in Arctic whales and polar bears, and they have PFAS, they have measurable PFAS. And but everyone has a different mixture of PFAS and variable concentrations. And we know a lot about the detrimental health of PFAS at this time. We know that they disrupt neurodevelopment, they are associated with several types of cancer, with immune disruption, with pregnancy, adverse pregnancy outcomes. But there's there's very little research on the association between PFAS exposure and late life brain health, particularly, particularly dementia and stroke. And so my area of research, my passion over the past, really over the past decade is to study PFAS exposure in relation to cerebrovascular disease and in particular dementia.

Dr. Michael Koren 26:25

That's really fascinating. And any conclusions that you can share with the audience that are actionable at this point, or is it still one of those things where these things are ubiquitous, we're not sure exactly how to interact with them or how to deal with them? I know you mentioned that they're in so many different things. I've heard at least the argument that they're supposedly not going to interact with biological systems. That's one of the arguments for them that they're unable to interact in many cases, but they are around forever. We don't break them down. So how do we deal with that on a practical basis?

Realistic Ways To Cut PFAS

Dr. Hannah Gardener 27:02

Yeah. So at this point, we don't have I don't have evidence yet from my cohort about the association between PFAS and late life brain health. There have been a few small studies that are mostly not prospective on PFAS and cognitive health, although there haven't been any prospective studies on dementia as the outcome. That is a gap in the literature that that my study seeks to fill. But we already have plenty of evidence that we should all be reducing our PFAS exposure because we there are many well-established known associations at this point. We know that PFAS exposure is associated with worse cholesterol profiles, with hyperlipidemia. We know that they are associated with disturbances to neurodevelopment and several cancers. They decrease the effectiveness of a vaccine. So there's plenty of evidence that nobody should be waiting around to reduce their exposure to PFAS. And there are many ways that we can reduce exposure to PFAS, despite the fact that they are all around us. They are very common contaminants in our water supply. And so I find a water filter that will reduce PFAS exposure and using those water filters is very important. Water is probably the biggest exposure source. Not consuming microwave popcorn is a way to reduce PFAS. You can't see PFAS. So we don't know which foods necessarily as consumers are more or less contaminated with PFAS. So what I tell people is variability. The more varied your diet is, both from what you eat and the brands you eat, the you will reduce your exposure to PFAS overall, and you will also reduce your exposure to other food contaminants like phthalates and bisphenols and heavy metals. So that sort of strategy works in a real broad sense. And when you're making big purchases, when you're buying a new couch or when you're buying new carpet, new rug, ask the manufacturer, do you use PFAS? If you asked manufacturers 15 years ago, that you would not get reliable answers. Most would not know. Over the past couple of years, that has really, really changed. And when you're buying clothing, there have been regulations in both California and New York starting last year that PFAS are no longer allowed in textile. So clothing brands that sell in California and New York, which is pretty much at all of them, they should be PFAS free. It never hurts to ask. There are brands that had switched from using PFAS years before. So they might be a little bit more reliable in terms of being PFAS free. But what I tell people is when you're when you're making big purchases, contact the company. Find out if you're buying a couch from Pottery Barn or Crate and Barrel or West Elm, like contact them and say, is this fabric PFAS free or not? IKEA is a brand that's really, really good at disclosing the fact that none of their textiles contain PFAS. So it's really helpful when brands are really transparent and public about that.

PFAS Blood Tests And Blood Donation

Dr. Michael Koren 30:33

Interesting. Interesting. Is that something we should get a blood test for? Is it something we can detect in our blood to determine if we're on the right track or the wrong track in terms of avoiding exposure to PFAS?

Dr. Hannah Gardener 30:45

That's a really good question. And until recently, that was pretty much unheard of. Now I believe you can go to Quest and get your blood tested for PFAS as a, you know, as a just as a regular person, not part of a research study. I mean, of course, it's been something that we have been studying in research for a long time. But now there is that the ability to get tested for people to have their blood tested. I think it's a little bit hard to interpret that data because you don't have a threshold level of danger necessarily. Exactly. It's sort of understood that everyone should be reducing their exposure. So what I tell people is, you know, every you're you're gonna find out that your blood uh that there's there's PFAS in your blood. I think it's more effective to really look around your environment and know that you are your blood is far more contaminated than you want it to be, and think about how to reduce that exposure. What can you do moving forward? Even just things like washing your hands, because you know, if PFAS are in our furniture, it's ending up in our house dust and normal hand-to-mouth contact makes you ingest PFAS. And so the more you wash your hands, the better. I think it's really important for people to think about their occupational exposures to PFAS, particularly, particularly firefighters. They're in terms of how to reduce your PFAS exposure, that's sort of something that a lot of health scientists are talking about these days. We know the good news and the bad news is that when you donate blood, you measurably decrease the the PFAS, the body burden of your own PFAS. Of course, that means that every time we are all donating blood, we are donating PFAS contaminated blood. Um, everyone should still donate blood. Donating blood is so important. But what I tell people is if if the idea of that being an effective way to reduce your PFAS exposure, if that gets you to donate blood, all the more reason. All right.

Dr. Michael Koren 32:58

Interesting.

Dr. Hannah Gardener 32:59

Unfortunately, when we deliver babies and we breastfeed, we are also sadly decreasing our body burden and we are giving it to our children. But there's a lot of things that people can do. There's a lot of personal care products that are contaminated with PFAS without us knowing. So again, the less you put in and on your on your body in terms of just products that you use, the less exposure you will have.

Dr. Michael Koren 33:23

Oh, you're giving another reason for kids to blame their parents for everything.

Dr. Hannah Gardener 33:28

Yes, especially the firstborn children, unfortunately, get a higher dose of that PFAS in general.

Dr. Michael Koren 33:34

Wow.

Where To Learn More And Close

Dr. Michael Koren 33:35

Well, this has been an absolutely fascinating conversation. I've really enjoyed every minute of it, but we do have to sort of conclude. And I think maybe the best way to conclude is how do people learn more about your work and learn more about the things that you're passionate about, both in the Diet Soda area and these other contaminants.

Dr. Hannah Gardener 33:55

Yeah, so there's a lot of ways to learn about my work. I uh all my publications are on PubMed. My name is Hannah Gardener. You can look up the work there. You can look up the Northern Manhattan study. I am also the BIOS statistics director of the Florida Stroke Registry, which we didn't talk about today, but we are doing some really amazing work in the Florida Stroke Registry. So people can look that up as well. And in terms of my personal business, it's called A-Green Slate Consulting. You can look me up on social media or my website and reach out. I'm always happy to help anyone who's interested in reducing their exposure to toxic chemicals without the stress and in a way that also really minimizes financial burden as well. Those are the two things that people thinking about reducing exposure to toxic chemicals makes people feel stressed and they think that it's going to cost a lot of money. And as I hope I have alluded to in this conversation, my goal is actually to help people save money and reduce their exposures.

Dr. Michael Koren 35:01

Well, we love that. Hannah, thank you very, very much for being a guest on MedEvidence.

Dr. Hannah Gardener 35:07

Thank you for having me.

Announcer 35:08

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