Cancer-related fatigue and brain fog are two of the most common concerns I hear from people during treatment and survivorship. These symptoms can have several contributing factors and may persist even after treatment ends. Understanding what may be driving them can help guide the next steps toward recovery. In this article, I’ll explore some of the potential causes of fatigue and brain fog, how to improve these symptoms, and when it’s important to seek medical care.

What Is Cancer-Related Fatigue?

Cancer-related fatigue is more than just feeling tired. It’s a persistent, often overwhelming exhaustion that doesn’t always improve with rest or sleep. Everyday activities, such as showering, cooking, or getting dressed, can take far more energy than usual, and you may find yourself needing to sit down or rest much sooner than expected.

You might feel physically drained, have difficulty concentrating, or notice that you’re more emotionally exhausted than usual. Fatigue can also vary considerably from day to day, fluctuate throughout the day, or change as you move through treatment. For example, it may worsen immediately after chemotherapy or build over the course of radiation therapy.

If this sounds familiar, you’re not alone. Cancer-related fatigue is one of the most common symptoms experienced by people with cancer and a frequent side effect of cancer treatment. Although it’s common, that doesn’t mean you simply have to accept it as something you must live with.

Understanding the factors that may be contributing to your fatigue is an important first step toward finding ways to manage it.

Why Can Cancer Treatment Affect Energy Levels?

There are several reasons why cancer treatment can affect your energy levels. Treatment places significant demands on the body, and depending on the type of treatment, it can affect healthy cells and tissues as well as cancer cells. Your body then needs time and energy to repair and recover, which can leave you feeling depleted.

Other factors can contribute to fatigue, too, including pain, emotional distress, disrupted sleep, anemia, nutritional deficiencies, and a loss of muscle strength and stamina. Underlying health conditions, such as thyroid disorders or heart, kidney, or liver problems, may also play a role.

Often, it isn’t just one thing causing the exhaustion, but a combination of factors that build on one another. Your body is managing a great deal during treatment and recovery, and understanding what may be contributing to your fatigue can help guide the next steps.

This is where a naturopathic approach can be helpful. Because cancer-related fatigue often has multiple contributing factors, I look at the bigger picture, including your treatment history, medications, supplements, nutrition, sleep, stress, and recent bloodwork.

The goal is to identify which factors may be contributing to your symptoms and determine what can be safely addressed to support your energy and recovery, always in coordination with your oncology team.

What Is Cancer-Related Brain Fog (“Chemo Brain”)?

Brain fog is another symptom people may experience during and after cancer treatment. You might walk into a room and forget why you went there, lose your train of thought, struggle to find the right word, or forget an appointment. Everyday tasks, like following a recipe, paying bills, or keeping track of a shopping list, may suddenly require more effort.

These changes are often called cancer-related cognitive impairment, or “chemo brain” when associated with chemotherapy. They can affect memory, attention, concentration, and executive function, which helps us plan, organize, and make decisions. Cognitive changes can begin before treatment, occur during treatment, and sometimes persist for months or years afterward. Even subtle changes can impact daily life significantly.

Why Concentration and Memory May Feel Different During Treatment

Some cancer treatments can affect the brain and nervous system, making it harder to concentrate, remember information, and organize thoughts. Treatment may contribute to changes in inflammatory signaling, oxidative stress (an imbalance between damaging molecules called free radicals and the body’s antioxidant defenses), and communication between nerve cells. Certain treatments can also affect hormone levels, which may influence memory, concentration, and sleep.

Other factors can add to these challenges. Fatigue, poor sleep, mood changes, pain, changes in appetite and diet, dehydration, blood sugar fluctuations, nutritional deficiencies, and electrolyte imbalances can all affect cognitive function. Certain medications, other health conditions, and lifestyle changes may contribute as well. The cancer itself, the emotional strain of diagnosis and treatment, and the body’s response to illness can also play a role.

In my experience, looking at the whole picture can help identify areas where additional support may be beneficial. A naturopathic doctor can help review nutrition, lifestyle factors, and potential nutrient deficiencies in coordination with your medical team.

Addressing contributing factors where possible can help support cognitive function and overall well-being.

Can Sleep, Nutrition and Hydration Affect Fatigue?

Yes. Sleep, nutrition, and hydration all play an important role in how we feel during and after cancer treatment. When your body is already working hard to cope with treatment and recovery, not getting enough rest, food, or fluids can contribute to fatigue and make it harder to concentrate.

Eating regularly and getting enough nourishment helps provide the energy and nutrients your body needs. However, treatment side effects such as nausea, poor appetite, changes in taste, or diarrhea can make this challenging. Working with a naturopathic doctor can help you navigate these changes and explore practical strategies to support your nutritional needs throughout treatment.

Staying hydrated is equally important, particularly if you’re losing fluids or struggling to drink enough. While rest is essential, gentle physical activity, as tolerated, can help maintain strength and stamina. Establishing a consistent sleep routine and making time for yourself may also help improve sleep quality and manage fatigue.

Small, realistic changes can be a helpful starting point. This might mean eating smaller, more frequent meals when your appetite is low, keeping fluids nearby throughout the day, prioritizing a regular sleep schedule, or incorporating gentle movement when you’re able. The goal isn’t to do everything, but to find what helps support you through treatment.

What Role Can Bloodwork Play in Understanding Low Energy?

Bloodwork can help identify some contributors to fatigue such as thyroid function, iron status, vitamin B12, vitamin D, kidney and liver function, electrolyte imbalances, blood sugar, and inflammation. Your oncology team often orders many of these already, so it helps to bring or request your recent results.

Bloodwork is one piece of the picture, read together with your symptoms, treatment history, medications, nutrition, and lifestyle. Normal results don’t mean your fatigue isn’t real, since many people have significant fatigue with unremarkable labs.

And if something does come back low or abnormal, how to address it should be coordinated with your naturopathic doctor and oncology team, because treatments, supplements, and timing can interact.

Why Symptoms Can Continue After Treatment Ends

Fatigue and brain fog often improve after treatment is finished but can continue for months or even years. Approximately 30% of patients still reported difficulties months or years after completing treatment.

There are many reasons this can happen. Lingering treatment effects, lost strength and stamina, disrupted sleep, ongoing stress and mood changes, pain, and the demands of returning to work and family life can all keep symptoms going, and often several are present together.

If your symptoms are ongoing and not improving, please tell your care team rather than waiting for them to fade.

When Should Fatigue or Cognitive Changes Be Reported to Your Oncology Team?

If you’re experiencing fatigue or changes in memory, concentration, or thinking, let your oncology team know. These symptoms are common during and after cancer treatment, but they shouldn’t be dismissed. Your care team can assess potential contributing factors and help identify appropriate support.

It’s especially important to report symptoms that are new, sudden, severe, worsening, or interfering with daily life. Fatigue accompanied by fever, shortness of breath, chest pain, dizziness, unusual bleeding or bruising, or unexplained weight loss also requires prompt medical attention. Sudden confusion, difficulty speaking, vision changes, or new weakness or numbness require emergency assessment.

Your emotional well-being matters, too. Cancer treatment and recovery can take a toll in ways that aren’t always visible to others. You may feel anxious about your health, frustrated by changes in your body or thinking, or exhausted by everything you’re managing. If you’re finding things harder emotionally, please don’t feel that you have to push through on your own.

Talking with a counsellor, connecting with a support group, or accessing psychosocial oncology services can give you space to work through what you’re experiencing and find support that meets you where you are.

Supportive Cancer Care During Treatment and Survivorship

Supportive cancer care is about helping you manage symptoms like fatigue and brain fog, supporting your nutrition and overall well-being, and making sure that any recommendations are safe and appropriate alongside your cancer treatment.

When someone comes to see me feeling exhausted or struggling with memory and concentration, I want to understand what they’re going through and how these symptoms are affecting their day-to-day life. I take the time to learn about their experience, review their treatment history, relevant bloodwork, medications, and supplements, and explore factors such as nutrition, hydration, sleep, physical activity, and stress.

From there, we work together to identify practical ways to support their health that feel manageable for them. This might mean addressing nutritional gaps, finding ways to improve sleep, or figuring out how to conserve energy throughout the day.

I recognize that everyone’s experience with cancer is different, so my approach is guided by your individual needs, priorities, and circumstances. My goal is to help you feel supported and work with you and your oncology team to find ways to improve your well-being throughout treatment and recovery.

Cancer Care Support in Toronto, Pickering, and Ajax

If you’re looking for supportive cancer care in Toronto, Pickering, or Ajax, you can book a complimentary 15-minute discovery call to talk about what you’re experiencing, what matters most to you, and how I may be able to support you.

Together, we can explore ways to support your energy and cognitive function, manage treatment side effects, and nurture your overall well-being. I look forward to speaking with you and learning more about how I can support you through treatment and recovery.

This article is for general education only. It is not medical advice and does not replace care from your oncology team. Supportive care complements, and never replaces, standard cancer treatment.