6 Surprising Causes of Brain Fog

Have you ever had that feeling where you’re lethargic, have poor memory, are forgetful, can’t concentrate on a task or wrap your head around difficult concepts, for no apparent reason? If you’ve experienced this or are currently going through it, you might refer to it as brain fog.

Brain fog is very common mid-afternoon when many are prone to an energy lull (which is fortunately largely avoidable). Some people however, experience brain fog all the time or at points in the day where previously they were very clear-headed and alert. You might even be experiencing brain fog and think that it’s normal. When a client comes to us and describes “brain fog” as a symptom, there are a few main things we take into account.

6 Surprising Causes of Brain Fog


The thyroid is a small but mighty gland located in the front of the neck that regulates the production and release of your thyroid hormones. Thyroid hormones are extremely important in that they regulate your body’s metabolic rate, bone maintenance and production, the heart and digestive function, mood, and more. Click here for some of the common symptoms of low thyroid.

Low thyroid slows everything down, including ATP production. ATP (adenosine triphosphate) is a chemical that provides energy for the cells. Since the brain is the highest energy consumer in the body, it is most affected by a decrease in ATP production. Brain fog and fatigue are so common with low thyroid that it has been dubbed “thyroid brain”.

Unfortunately, low thyroid often goes undetected with standard TSH tests done through your family doctor because the acceptable range is considered much too wide for optimal health. This is why whenever we suspect low thyroid we test for multiple thyroid hormones (T3, T4, TSH, thyroid antibodies) to get a better picture of what’s going on and find the root cause.

Disruptions to your circadian rhythm

Your circadian rhythm is your body’s 24 hour internal clock that regulates when you’re alert, tired and asleep. Disruptions to your circadian rhythm from a time change, shift work or an irregular sleep schedule can be to blame. If you have control over your sleep schedule, developing a routine for when you wake up go to sleep, and even the time frame within which you eat your meals, can be a really important first step.

Low Iron

Iron is needed to make hemoglobin, which is the substance in red blood cells that carries oxygen throughout your body. If your levels are low it means that not enough oxygen can reach the brain. If you are feeling unusually tired, I always recommend starting with a blood test from your family doctor to check your iron levels. Review the results yourself. We see it all the time where someone has low iron but their doctor doesn’t flag it, or their levels are just on the cusp of being low and they are not told, yet it’s low enough to experience symptoms. More on that here.

Blood sugar imbalances

Blood sugar imbalances are the most common cause of brain fog and usually the main reason for the afternoon energy slump. If blood sugar levels dip below a normal range, your cells and brain are not receiving the energy they need to function properly. The main culprits when it comes to blood sugar imbalances are the obvious ones like a diet too high in sugar or refined carbohydrates like flour, skipping meals and overeating. Eating a very low carb diet or a diet that is far too high in even healthy carbs can also cause blood sugar imbalances.

A big contributor you may not be aware of though is your breakfast. If your breakfast is high in carbs and/or sugar and low in protein and healthy fats (i.e. cereal, bagels, toast or even a smoothie with several cups of fruit) it’s going to spike your blood sugar levels. I’d also recommend taking stock of how much sugar, even healthy sugar, has creeped into your diet lately. A few dates here, a cookie there, some chocolate here, can have a bigger than you might expect.

Sex Hormone Imbalances

With the advent of the birth control pill, and hormone disruptors, it can be very common to see women with imbalances in their sex hormones. Symptoms of such imbalances can include irregular periods, low libido, PMS symptoms, and fatigue not resolved by sleep. As an example of how this can impact your energy (and brain), low progesterone levels can cause blood sugar imbalances and can increase feelings of anxiousness, which have an impact on mood and energy levels. Low estrogen is also linked to lethargy and an inability to concentrate. Here are some ways to balance your sex hormones regardless of if you are approaching menopause or now.

Cortisol Imbalances

Cortisol is a stress hormone released by your adrenal glands. If you’ve recently gone through a very stressful period you might feel more burnt out and unmotivated than usual until your body can bounce back. The problem is when the stress is long-term and you don’t make up for it with downtime or proper stress management, or you add on other sources of stress or inflammation (more on that here). Your HPA-axis (hypothalamic–pituitary–adrenal axis) can become dysregulated and your cortisol levels may be affected. Sometimes this means low cortisol and fatigue in the morning, other times it could mean low cortisol all day and then higher levels at night, leading to sleep problems. This can have a major impact on your mental performance (source).

Usually there is never just one cause of brain fog, but in many cases, cortisol is implicated in some way. Emotional or mental stress aren’t the only things that can trigger a stress response. Blood sugar imbalances and inflammation (such as inflammation in your gut) are other examples of types of stressors on the body. Whenever your body is experiencing stress, whether physical or emotional, the “fight or flight” response is activated and the stress response takes priority. This can lead to imbalances in your sex hormones, thyroid and further exacerbate or cause blood sugar imbalances.

If you suspect this is something you're dealing with and would like more info on how we work one-on-one with clients to address fatigue and brain fog, please book a complimentary info session below.

Written by: Natalia Bragagnolo, RHN

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