Chemo Brain Explained: Why Brain Fog Happens After Cancer and What Can Help

 What is chemo brain? In this episode, oncology dietitian Dr. Krystle Zuniga explains cancer-related cognitive impairment (CRCI), why it happens after cancer, and what current research says about exercise, nutrition, sleep, stress, and other strategies that may help support cognitive function. 

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SPEAKER_00 0:17

Hey friends, welcome back to Cancer Nutrition HQ. I'm your host, Dr. Crystal Zuniga, oncology dietitian. Friends? Yep, I decided that's what I'm calling you because I realize that these episodes have started to sound a little more formal than I had intended. And this was never meant to feel like a dry lecture series or like you're back in school. Honestly, even when I'm teaching classes, I'm much more conversational than I've been on this podcast. So I'm making a small change. I'm still going to bring you the science. I'm still going to dive into the research, but I do want these conversations to feel like we're just sitting down together, talking through the evidence in a way that's practical and approachable, kind of like what I've done on my Instagram lives, which I know I haven't done in a while, but I missed them. So I'm bringing that here. So welcome friends. I am glad you're here. Now let's get back to the content. So today we're beginning the deep dive series into the challenges that could start during treatment and linger even after active treatment has ended. Maybe this scenario sounds familiar. You walk into the kitchen because you went in there for something, but you find yourself maybe staring at the refrigerator, asking yourself, wait, why did I come in here? Then the oven timer starts beeping. Oh yeah, I was baking something. Then as you turn that off, your phone alarm goes off because you needed reminders to take your medication. And then your partner or kid asks you a question from the other room and halfway through answering, you forgot what you were even talking about. These little moments start to feel less like minor blips of everyday forgetfulness and become more frequent and more disruptive. Your brain isn't working the way that it used to, and that can be frightening, especially if you're wondering if that's a new brain metastasis or if you have early dementia. And many cancer survivors describe these cognitive changes as brain fog or chemobrain. But this common side effect of cancer and its treatment actually has a clinical term, and it's called cancer-related cognitive impairment. So in today's episode, we're going to talk about this cancer-related cognitive impairment, what it is, why it happens, and leaving you with some practical ways to help support your brain. First, we need to stop using the term chemobrain. And I know I still use it because that's what people are calling it, but this phrase chemobrain initially became popular because chemo was one of the first cancer treatments strongly associated with cognitive changes. But now we know that these changes are not just limited to chemotherapy. We've seen it happen in those with radiation, immunotherapy, endocrine therapies. So we're going to use the medical term cancer-related cognitive impairment. And this has a definition. It's defined as the loss of mental acuity associated with cancer and its subsequent treatments. And it's not because I'm trying to be overly technical, it's because it's important to acknowledge that these changes aren't just from chemotherapy. Again, these difficulties have been identified in survivors across all types of treatments, and it's even been identified before treatment even starts. And I'll explain a little bit more about why we see that later. And the incidence of cognitive impairment also varies quite widely across different studies because of the variation in how it's measured. Because right now, there isn't a single test or brain imaging study that diagnoses the issue, which makes it harder to identify and treat. For example, although someone might report a lot of significant changes through a questionnaire, when you do the testing, it's coming out, quote, normal. Or the opposite has been seen as well, where they're not doing well on these cognitive tests, but they're not reporting any difficulties. So with those challenges, we have seen quite a range in the incidents. Studies reporting anywhere from 19 to 78% of cancer survivors experiencing some degree of cognitive difficulties. I've heard survivors describe it like their brain isn't working the same, like it's working slower or feels foggy. Like it's not just one thing that is difficult, it's focus, organizing, memory. And this aligns with what we've seen in the research because cancer-related cognitive impairment can impact multiple domains of cognitive function. But some of the deficits have shown up in memory and learning. So that's struggling to retain new information or even remembering where you put your car keys, concentration and attention. So finding it more difficult to stay focused at work, read a single paragraph, or even follow a discussion, difficulties with reasoning and executive function, because there's a mental processing required to kind of organize your day, prioritize things, multitask, make complex decisions. Deficits have also been seen in visiospatial memory and processing speed. So that might feel like your brain is taking twice as long to process a visual cue, react to a sudden change, like when you're driving a car. Some survivors have even reported feeling uncomfortable driving because their brain just isn't working the same. So basically, cancer-related cognitive impairment can affect things as little as forgetting where you left your keys, to holding a conversation, staying focused at work, or making complex decisions. But another challenging part of this research area, it's not like all of these things are happening in all survivors. How many domains are impacted, how severe these changes are, and how long they last vary by individual. As I mentioned earlier, cognitive symptoms may show up even before treatment begins. It can persist for months or even years after treatment ends. There's estimates that cognitive changes persist in up to 35% of survivors. A landmark study was published by Koppelman's and colleagues in the Journal of Clinical Oncology. And in that study, they compared cognitive function in breast cancer survivors that were on average more than 21 years post-chemo and compared it with women from the general population without cancer. The breast cancer survivors performed worse on cognitive tests across multiple domains, including learning, verbal memory, and processing speed. And interestingly, they published another study using brain imaging. And from that same sample, they showed that the chemotherapy-exposed breast cancer survivors had significantly smaller total brain volume and gray matter volume. So we know this exists. We have research that shows it can begin before treatment can persist, results in changes in cognitive function and even brain structure. But what I think is really important is to hear from survivors themselves about how it impacts their life. So I asked my audience on Instagram to share some of their experiences. One survivor said, chemo brain is no joke. It's like a fog that comes over you during treatment. It takes a while to set in. It doesn't happen immediately. Your memory starts to get worse and you struggle to find words. It can take years to go away, and I'm still dealing with a tiny bit. I have recovered quite well, but it's been years. I'm in my eighth year out from the inception. My doctor and my therapist both see a huge difference at this point, but it did take years to go away. Another survivor reported frustration with how long this has stuck around as well. After chemo was completed, it took two years to feel like the fog was lifting, but I still don't feel completely normal. I guess I've gotten used to a new normal. And this isn't just impacting the day-to-day, it can impact people's ability to work. One survivor reported, I remember sitting down one day to write a grant for an organization that I've worked with for years. And I just sat there looking at my screen for 10 minutes in tears because I couldn't even figure out what to type. My brain was blank. I have struggled with this off and on since chemo, and I'm on tamoxifen, and it's genuinely caused me anxiety. So much so that I've been contemplating a career change. Another survivor reported how it influenced their ability to go back to school. I ended up dropping out of my master's program due to it. My brain just no longer functions the same. I'm constantly tripping on the right words to use, my memory is awful, and my attention span is out the window. Thank you to everyone who shared your experiences because your stories really help illustrate just how distressing and life-disrupting these cognitive changes can be. And I share all of this info on the incidents and the severity, not to scare anyone, but hopefully to help validate what many survivors report. This is not rare, and it is not simply a matter of being distracted or not focusing hard enough. And a positive note, though, is that there is more research in this area into what is causing it and what we can do about it. And I'm going to share that with you today. So, as I said earlier, these changes aren't limited to those receiving chemotherapy. So, what is actually the cause? Well, that's been the tricky part about finding a treatment, because there is no singular cause. Cancer-related cognitive impairment is usually multifactorial, meaning there are several factors that could be contributing, from cancer treatment to psychological and physiological influences. Great, right? Another complex cancer issue. Nothing is simple in this area. But let's discuss some of the contributors, starting with the ones that are non-modifiable. So cancer treatments themselves can impact brain function. Some chemotherapies or their byproducts can cross that blood-brain barrier, damaging brain cells. Radiation in the brain or the head and neck area could alter structures of the brain or blood vessels that are delivering oxygen and nutrients to the brain. So that's going to impact brain function. Now, those are examples of direct damage, but these treatments also have indirect effects, like through inflammation. Yeah, inflammation is involved in a lot of things because both the cancer itself and treatments like chemo and radiation trigger the production of inflammatory cytokines in the body. And this systemic inflammation can trigger localized neuroinflammation, so that inflammation in the brain. That can cause damage to neurons, which are a type of cell that's in the brain, and changes in neuronal function. Some treatments can also be cardiotoxic, meaning they damage your heart and blood vessels. So if blood vessel health is affected, that may influence the blood flow, the oxygen delivery, and the integrity of that blood brain barrier that's supposed to keep bad things out. But also poorer nutrient or oxygen delivery to the brain also means less fuel to the brain. So this is another reason why that cardiovascular health really matters in survivorship, because what supports the heart and your blood vessels is going to support the brain too. Changes in hormone production andor signaling also has consequences for brain function. And this is particularly important for the women thrown into medical menopause, like breast cancer survivors, because estrogen is not just a reproductive hormone. Estrogen receptors are widely distributed throughout the body, including the brain, especially in the areas that are responsible for memory and executive function. So these endocrine therapies like aromatase inhibitors or tamoxifen, they can cause this drop in estrogen signaling. So your brain is getting deprived of a signaling molecule that it relies on to really function at its best. Now, this does not mean hormone therapy should be stopped. We know that these therapies are essential for reducing recurrence risk or controlling disease, but it is important for breast cancer survivors to know that although they may be done with the primary treatment, those endocrine therapies can also cause cognitive symptoms. And many survivors are on this for five to 10 years. So you may be struggling with these issues for a few years. And the psychological stress and anxiety that comes with a cancer diagnosis can also keep your brain stuck in this sympathetic, quote, survival mode. When your brain is hyper-vigilant, constantly scanning for the next threat, it has a reduced ability to focus on non-survival tasks, like organizing that work project or remembering a word in your conversation. Combining that high stress with treatment-related fatigue, sleep disruptions, your brain is lacking that restorative downtime that it requires to consolidate your memory's clear cellular waste and again function at its best. Now there are more potential contributing factors to cancer-related cognitive impairment, and we know some people are at higher risk than others, but I want to shift away from discussing the mechanisms to what you can actually do to support your brain health. I think this was enough to kind of lay that groundwork for you to understand that this is complex. So we're going to need a multifactorial way to approach brain health as well. Because of that complexity, there's not going to be a single pill, supplement, or a quick fix that's going to reverse it. There has been quite a bit of research in this area that has tested a variety of approaches in some small clinical trials, cognitive rehabilitation, computerized brain training like brain games, mindfulness-based interventions, cognitive behavioral therapy, and even medications like stimulants. Now, some of these interventions have shown some modest benefits for certain patient populations, but the results have really been mixed. So none of those interventions has emerged as a universally effective solution. But the good news is there is one strategy that has consistently risen to the top of the evidence. Do you want to take a guess at what that is? Exercise. Yes, exercise is one of the most consistently helpful strategies because when you exercise, there are both short-term and long-term benefits for brain health. So in that short term, you're increasing blood flow, your heart rate's increasing, and that also results in an immediate increase in blood flow to the brain. This is going to rush a fresh wave of oxygen and nutrients directly into your brain. We've also seen that exercise stimulates the production of molecules like brain-derived neurotrophic factor that signals for developing new neurons. And I'll share a little bit about what the long-term data says about that too. Very exciting stuff. Now, on the days that you move your body, you might also see acute, immediate improvements in your energy levels, your mood, your sleep quality. All of those factors are going to help you feel like your brain is functioning better. Even acute bouts of exercise have been demonstrated to improve cognitive performance. In one study of breast cancer survivors, improvements in both processing speed and spatial working memory were seen in as little as 10 minutes of walking. So physical activity is a nice brain boost. And over time, the benefits can be even greater. Because long term, you can literally change your brain. Because those improvements in cardiovascular health, if you're keeping up with your aerobic exercise, is improving the elasticity of blood vessels. So that's going to improve blood flow, that oxygen and nutrient delivery, even outside of those exercise sessions. Because exercise does have a metabolic demand, it actually helps signal for increases in the production of mitochondria, those powerhouses of the cell, which help you produce energy. So more mitochondria means better energy production, so your neurons are able to function more quickly. And over time, regular exercise acts as a potent anti-inflammatory agent. So, yes, acutely exercise can increase inflammation, but long term, it actually has anti-inflammatory effects because the body learns how to handle that stressor more effectively. And another benefit is improvements in your metabolic health. Regular exercise improves insulin sensitivity. What that means is that when there's glucose available, your brain cells are going to be better at picking it up and using it for fuel. I know I'm a nutrition podcast and I talk about exercise a lot, but that's just because the evidence is so strong for exercise. For example, just a couple of months ago, an umbrella review, and that means a review of other systematic reviews, was published in the journal Psychooncology. It included 80 primary articles to represent a total sample of over 7,500 participants. And this analysis of this research reported improvements in objectively and subjectively measured cognitive function in cancer survivors. So moving your body is a great way to support your brain health both acutely and long term. So if you're having some trouble focusing at work or saying on task in your chores, go for a short walk. You might find it helps you get back to functioning a little better. So another strategy that can be helpful are mind-body techniques. Stress regulation and mind-body strategies can also support cognitive function. These mind-body techniques can help settle your nervous system because cognitive symptoms often worsen when you are stuck in this stress response. Chronic stress keeps this brain in a type of survival mode. It's constantly on high alert, again, looking for another threat, which is fantastic if you're trying to run away from a bear attack, but it's completely useless when you're trying to organize a spreadsheet at work or say focus on a presentation. Practices like mindfulness meditation, breath work, or gentle yoga are tools to help bring the nervous system down from high alert. These aren't woo-woo things. And trust me, I thought that they were woo-woo things. But after seeing the research, I am confident in recommending these to survivors to help improve different areas of cognitive function. And if you're struggling with anxiety, depression, or PTSD symptoms, or this distress after cancer, highly recommend that you seek out some professional mental health support. Therapy, support groups, even medication when appropriate can all be important. Your mental health is directly impacting your brain function. Now, our next foundational pillar is sleep. When you sleep, specifically when you're achieving that deep restorative sleep, your brain's able to do this memory consolidation. And what that is, is it's essentially organizing all that information you gather throughout the day, moving it from that short-term holding storage to long-term storage. I like to think of the example of like you bring in the mail and you just put it on the kitchen table. That's like your short-term storage. And then when you actually file it away, get rid of the stuff that you don't need, throw that away, pay your bills. That's kind of what your brain is trying to do. What's important, what's not important. Let me store the stuff that is important. And sleep is also when the brain's lymphatic system opens up. And that's a system that literally flushes out waste from the brain. So less trash around, it's going to be able to operate better. But unfortunately, for many cancer survivors, I know sleep can be very difficult. So to combat this, we have to practice some good sleep hygiene. Try to maintain highly consistent sleep and wake times, even on weekends, even on vacations, even on holidays. Try your best to stay on track. You might consider keeping a little better tabs on your caffeine because even if you feel tired enough to fall asleep with caffeine in your system, because that cancer-related fatigue can be very exhausting, caffeine is still in your system and it's blocking your ability to really get into that deep restorative sleep. You might start with a strict rule of no caffeine after lunch or aiming for eight to 10 hours of no caffeine before bed. And I have to address something I've seen a lot in patients is this revenge bedtime procrastination. Because the brain is just firing slower during the day and you're also dealing with cancer fatigue, you might be feeling less effective, less productive that you didn't get enough done. So out of this sense of guilt or frustration, you stay up later, trying to force yourself to get more work done. But then what happens? You have cut your sleep short. And then you wake up in the next morning, you're completely exhausted, your brain fog's worse, you're more fatigued, your productivity has dropped even lower. So you're just in this vicious cycle. So sometimes the most productive thing you can do for your brain is to go to sleep. Staying up later is not going to solve the problem. You have to meet your body's need for rest. And if physical symptoms like hot flashes or pain or GI issues are keeping you awake, definitely talk to your medical provider. There could be some strategies that help with that. Now, I often tell my patients, and you might have heard me say this on Instagram meet your body where it's at. And this includes meeting your brain where it's at. A lot of frustration comes from trying to force your brain to operate the way. It did before cancer. But you can help it by using some tools that reduce cognitive load. Stop multitasking. Stop multitasking. I'm repeating that for myself as well. We all have trouble with that. But close those extra tabs, turn off notifications when you're working on something important. Maybe set some focus work blocks or times that you're going to take breaks. Another strategy is to put your most important tasks during the time of the day when your brain tends to work best. And that's not always the morning for some people. Maybe it's middle of the afternoon. And use all of the tools available to you: reminders on your phone, calendars, checklists, post-it notes, medication organizers, whatever helps you function better. That's being resourceful. Another thing I have a lot of survivors do, especially when it comes to nutrition, is reduce decision fatigue by just simplifying the routine. For example, repeat easy breakfast, keep the same running grocery list, create systems for the tasks that you're repeatedly doing. Because if you reduce the amount of energy your brain has to spend on things like remembering what you need to purchase, what you need to cook, what you need to eat, this is going to save some energy for you to use it on other things that your brain needs to do. So rather than getting caught up in this, why can't I do everything like before? I get it, it's frustrating. But how can you instead shift that to how can I reduce the load on my brain today? That can help you feel a little better. All right. Thanks for sticking with me with those other tools. Now we're going to talk about food. And I intentionally saved nutrition for the end because I want you to see that recovery requires a multi-pronged approach. I love nutrition, but nutrition alone won't fix your brain fog. But the dietary choices you make on your plate can certainly provide some help because it is the literal fuel behind your brain power. Fun fact: despite your brain making up only about 2% of your total body weight, it consumes roughly 20% of your body's baseline energy and oxygen. It is a very metabolically demanding organ. So if you want your brain to heal and fire quickly, you must give it some good fuel. That means you gotta feed it. This is not the time to use extreme, severe calorie deficits, fasting, restrictive diets, because when you severely restrict your caloric intake or you're skipping meals for a long period of time, you're depriving your already struggling brain of steady energy. So that can worsen some of this cognitive dysfunction, shortening your attention span, worsening your fatigue. You're likely thinking, okay, duh, Crystal, eat, but lots of people don't do that. So I do have to address that. But yes, there are other things that can help. And this is a really cool area of research. And fun fact, the research I did on this in my postdoc and early academic career was some of the early work in this space on diet and cancer-related cognitive impairment. I wish that it was a more popular research area based on just how distressing this issue is. But we do have some preliminary evidence that shows what actually you might expect. Eat your fruits and veggies. And I'm not kidding, fruits and vegetables really are powerhouses. In 2019, a systematic review published in the Journal of Cancer Survivorship reported that there was preliminary evidence that greater fruit and vegetable intake is associated with better cognitive functioning in cancer survivors. Two of my published papers in this area were actually included in that review. But my studies and the other studies that were in that review are all correlational and still included relatively small samples. What we do know is that fruits and vegetables are really good sources of antioxidants and phytonutrients like flavonoids and carotenoids that can actually cross that blood-brain barrier to help reduce oxidative stress and inflammation that impacts your brain. So aim for that colorful abundance of berries, your leafy greens, your yellow, orange, and red veggies daily. Another thing you can do is not restrict carbs. Carbohydrates are your brain's preferred fuel source because it is very efficient and rapid to get energy out of. But the type of carbohydrate matters. If you're leaning on those simple, highly refined carbohydrates like sugary drinks, white bread, you're going to cause this rapid spike in your blood glucose. And what goes up must go down. And the higher it is, the steeper and more dramatic that crash can be. And so the moment that your blood sugar crashes, your brain fog is going to come back with a vengeance. So instead, focus on complex carbs. These are the fiber-rich carbohydrates that provide a steadier release of glucose. So that's going to help maintain a good fuel source for your brain without the crashes. Some good examples are your oats, other whole grains, beans, lentils, fruit, veggies, plants. Eat those plants. Protein's also important here, too, because you need to meet your protein intake to support that repair of tissues. And neurotransmitters, which are these signaling molecules that are going between brain cells, they are built directly from the amino acids that you get from your diet. So ensure that you're getting good protein sources like your chicken, your fish, tofu, legumes, spread throughout the day. Carbs are important, protein is important, and fat is also important. So all of the macronutrients are needed, but your brain is made up of 60% fat. And over a third of that is the essential polyunsaturated fatty acid, omega-3s. You can find these abundantly in fatty fish like your salmon, sardines, mackerel. Some smaller amounts can be found in plant-based sources like your walnuts, chia seeds, ground flax seeds. So aiming to get some omega-3s from your diet can also help support your brain function. And even back to the basics of drinking your water. Even mild dehydration has been shown to affect brain function. I'm not going to get into all of the micronutrients, but some nutrient deficiencies can also contribute to some cognitive symptoms like a vitamin B12 deficiency or iron deficiency. So if the brain fog is persistent or worsening, it is worth discussing with your medical team and not just assuming that it's just standard, you know, chemo brain. Well, see, there I go again. That it's not standard cancer-related cognitive impairment. There could be some thyroid issues or a nutrient deficiency that needs to be addressed. Wrapping this all up on the diet section, there's no magic supplement. There's no magic superfood, a well-balanced anti-inflammatory dietary pattern that's focused on a variety of plant foods, unsaturated fats, and good quality protein is giving your brain the fuel and building blocks it needs. Now, in wrapping this up, I understand that these cognitive changes can feel embarrassing, frustrating, scary, especially when they're affecting your work, your conversations with your friends, appointments, or even your day-to-day tasks. But I want you to know that the research shows that for the vast majority of survivors, cognitive function will improve over time. I know you want it to go faster, but instead of trying to rush it, simply support it. And today we discussed several strategies. So that's my action item for you this episode. Choose a way that you're going to support your brain. Is it exercise, taking a walk in the morning, eating breakfast, writing things down, setting a reminder, going to bed a little earlier, asking for referral to talk to a therapist, or maybe it's just continuing what you have been doing and being more patient with the process. But show yourself some compassion. Give your brain the fuel that it needs, give it rest, support your body the best you can. Now, if this episode helped you understand cancer-related cognitive impairment a little better, I would love if you shared this with another survivor, a clinician, a caregiver who needs to learn more about this topic. I hope this episode provided some validation for you as well, using the science to help you understand what's going on and what you can do about it. Again, stay tuned because I'll be discussing some more issues that come up in survivorship. I think next I'll be doing, I think, cancer-related fatigue, which, spoiler alert, aligns a lot with this cancer-related cognitive impairment issue. But stay tuned for that. Thank you for listening to Cancer Nutrition HQ. And as always, remember to eat your fruits and veggies.