What Causes Foggy Brain?

Illustration for article titled What Causes Foggy Brain?
Illustration: Benjamin Currie (Gizmodo)

If you’re like me, you can barely read this paragraph right now. I’m amazed I’m even capable of writing it. Most of us suffering from brain fog can recall a time, perhaps illusory, when setting and achieving goals was simple, more or less—when the main impediments to accomplishment, or simply making breakfast, were external to ourselves. We wonder: how did it happen? Is it aging, or luck, or diet, or what? Can it be reversed? For this week’s Giz Asks, we reached out to a number of experts to find out.


Leigh Charvet

Associate Professor, Neurology, NYU Langone’s Multiple Sclerosis Comprehensive Care Center

Brain fog is a very interesting topic because this a frequent complaint but often difficult to measure with clinical neuropsychological evaluation. When it occurs in the context of illness, such as what is referred to as “chemo brain” in cancer patients, there can be some corresponding problems in the areas of attention, information processing, and working memory.

In otherwise healthy people, brain fog is often described as something like being “out of it” or “offline” when required to pay attention to new information or when trying to process information for figure something out. People also can report greater difficulty making and executing plans. This is typically episodic and is hard to capture, and what is probably most sensitive is to characterize sustained cognitive functioning. For instance, brain fog may be captured when the person is required to maintain vigilance and consistency over a long task.

In the context of illness, and including drug effects, it is possible that the experience of brain fog is broadly due to less glucose (the main brain fuel) availability. That is, energy resources including glucose have been allocated to managing the body’s inflammation or metabolic needs, and decrease overall level of arousal. In this manner, the body being in a reduced state—for instance due to sleep loss, or being hungover, or not eating well—could contribute to the experience of brain fog in otherwise healthy people. I believe that another contributing factor can be stress, including with worry, anxiety, and depression. Stress can increase metabolic demands, and also alter hormonal and neurotransmitter function. Additionally, if there is a strong inner dialogue, for instance with rumination or worry, this can utilize the brain’s resources making them less available for any presenting cognitive demands.

Cyrus Raji

Assistant Professor, Radiology, Washington University in St. Louis, whose research focuses on the intersection between lifestyle factors and MR imaging biomarkers of brain health, among other things

Brain fog in otherwise healthy adults can result from a combination of lifestyle factors including but not limited to 1) chronic sleep deprivation, 2) unhealthy dietary choices particularly those high in refined carbohydrates and sugars and 3) lack of physical activity. Chronically, these problematic lifestyle choices can result in increased risk of cardiovascular disease, cancer, and even Alzheimer’s dementia. Short term, they can definitely result in what we refer to as ‘brain fog.’

Susan Davis

Professor, Public Health and Preventive Medicine, Monash University, and a Senior Principal Research Fellow of the National Health and Medical Research Council of Australia

As women go through the hormonal changes that occur at menopause and in the early post menopausal years many described “brain fog” or one of my patients said “washing machine brain.”

What they described is less clarity of thought, decision making being more difficult, walking into a room and forgetting what they were intending to do in that room, or starting a sentence and then lose track of what they were going to say. Impaired verbal fluency has been documented in perimenopausal- early postmenopausal women as well as reduced word finding, but the effects are subtle. this is because they are not dramatic like a head injury—affected women are still functioning in the range that would be considered normal, but perhaps not normal for them.

Although “brain fog” and subtle changes in memory have been linked to menopause the exact reason why this happens remains uncertain. Lack of sleep is an important component as we consolidate memory when we sleep—if sleep is repeatedly disturbed by hot flushes/sweats then memory will be affected. Although the hormonal changes are implicated as a root-cause, this is still an uncertain area. But the symptoms are common and the experience for women is real. Many find it very distressing and become quite worried they are showing signs of early dementia.

Some women say they are much better with hormone therapy- studies do not show a clear effect over placebo, but if women’s flushes are alleviated, sleep improved and anxiety lessened (anxiety is also a menopausal symptom) then women will think more clearly.


Rachele Pojednic

Assistant Professor, Nutrition, Simmons University

From a nutrition perspective, brain fog can be caused by a variety of issues. The three main culprits are 1) you’re just simply hungry, 2) you’re dehydrated or 3) you’re suffering from a major sugar crash (likely caused by breakfast or lunch high in simple carbs).

If you’re hungry, your blood sugar is likely low and so your brain is suffering from a lack of fuel (i.e. glucose). The best thing you can do is top off with a high fiber meal or snack which will slow-release glucose into your blood stream to address the fuel shortage. If you’re dehydrated, your brain (which is largely made of water) is likely not getting all the nutrients it needs because the delivery system is impaired. You can tell if you’re dehydrated by the color of your urine (you want it to be very pale yellow). The last major reason your brain might feel foggy is if you have eaten a meal a few hours earlier that was high in simple carbohydrates (i.e. a pastry for breakfast or a big sandwich with a full sugar soda for lunch). When you have this major rush of sugar into your system, your body works overtime to store it all as fast as it can. This system can overcompensate and deprive your brain of the glucose it is craving. Often times, this leads to a mid-afternoon sugar craving, which starts the whole cycle over again.

The best thing to do is eat a breakfast and lunch high in protein, healthy fats, and fiber-rich carbohydrates (i.e. eggs with a side of berries or a big mixed veggie salad with chicken) to keep blood sugar from fluctuating. Those types of meals will also provide other essential nutrients (i.e. vitamins, minerals, omega-3 fats) to keep your brain revving full force!


Daniel Levitin

Neuroscientist at the Keck Graduate Institute, and author of the NYT bestseller The Organized Mind and the forthcoming Successful Aging: A Neuroscientist Explores the Power and Potential of Our Lives

Brain fog is often caused by some parts of the brain sleeping—taking a nap—while other parts of the brain are not. Awakeness and consciousness are not binary things (on or off). The brain has thousands of special purpose processing modules. Some are working when others are not. If you set down your car keys and then can’t find them later, the part of your attentional system that should have been taking notice was probably off-line, catching up on some much-needed down time.

Of course brain fog can also be caused by drugs, sleep deprivation, brain disease, and Alzheimers, and in those cases it may not simply be that the area of your brain is offline temporarily—it may be a somewhat permanent or chronic condition due to pathological disturbances with brain tissue.


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Thanks for this! I have brain fog from an invisible illness (fibromyalgia and arthritis), and it is so embarrassing at work! I have to take notes constantly to try to keep up.