What’s Causing My Brain Fog?

Have you ever walked into a room and forgotten why you went there? Struggled to find a familiar word? Or reached the middle of the afternoon and felt as though somebody had quietly switched off your brain?  Occasional lapses happen to everyone, particularly during periods of stress, poor sleep, or illness. However, ongoing brain fog, poor concentration and memory difficulties can understandably feel worrying, particularly if you have had relatives with dementia or Alzheimer’s disease.

But brain fog and cognitive decline are not the same thing. Brain fog is really just when we get a bit of forgetfulness, thinking more slowly than usual, or having difficulty concentrating. Whereas cognitive impairment involves actual measurable changes in abilities such as memory, language, reasoning, or planning.

Brain fog can still be debilitating though. And there are many reasons for feeling mentally less sharp. Lack of sleep, menopause or hormone imbalance, stress, sluggish thyroid, or deficiencies of iron, vitamin B12 or folate can all contribute. But what is particularly interesting is that research is increasingly suggesting that metabolic health also matters to the brain. The way the body manages glucose and responds to insulin may influence how alert we feel today, as well as some of the biological processes involved in cognitive ageing. 

Don’t worry – this doesn’t mean that eating sugar causes dementia or that balancing blood sugar can guarantee protection from it! The relationship is far more complex. But getting our blood sugar under control can have a positive effect on the way we think.

Why Blood Sugar Matters for the Brain

The brain is an exceptionally energy-demanding organ. Even though it is only around 2% of our total body weight, it uses approximately 20% of our body’s energy at rest. That is significant.

Much of this energy is supplied by glucose circulating in the bloodstream. Brain cells need a continuous supply of energy to communicate, maintain their structure and support attention, learning and memory. However, before you start reaching for the biscuits, this doesn’t mean that more glucose is always better. The brain depends on the body keeping blood glucose within a carefully regulated range.

After eating carbohydrate-containing foods, glucose enters the bloodstream and the pancreas releases insulin. Insulin helps glucose move into muscle and other tissues, where it can be used or stored. Insulin also acts within the brain, where it is involved in communication between nerve cells, strengthening and forming connections, appetite regulation, and processes associated with learning and memory.

Problems may arise if cells become less responsive to insulin - known as insulin resistance. The pancreas initially compensates by producing more insulin, so glucose results can remain apparently normal for some time. This compensatory rise in insulin is called hyperinsulinaemia, and it means that the body is having to work harder to maintain glucose control, even though fasting glucose or HbA1c may still be withing range on a blood test.

Researchers have identified that disrupted insulin signalling within the brain may affect how nerve cells produce energy and communicate with one another. The hippocampus, a region involved in learning and memory, appears particularly sensitive to metabolic and vascular changes.

Inflammation, Insulin Resistance and Cognitive Function

Insulin resistance and inflammation can reinforce one another.

When cells respond less effectively to insulin, glucose and insulin may remain elevated for a longer time after eating. And over time, this may contribute to oxidative stress, altered fat metabolism, and the production of inflammatory signalling molecules.

Inflammation itself is not always harmful. It is an essential part of the immune response and helps us respond to infection and injury. The concern is more the persistent, low-grade inflammation that continues quietly over months or years. Visceral fat (or fat stored round the belly) may be one source of this inflammation. It can release inflammatory signalling molecules and is closely associated with insulin resistance. And it’s important to remember that people can develop metabolic dysfunction at many different body weights. 

Inflammatory signals produced elsewhere in the body can communicate with the brain. They may affect the blood-brain barrier, the carefully regulated boundary controlling what passes from the circulation into brain tissue. They may also influence microglia, the brain’s resident immune cells. Microglia normally help defend the brain, clear damaged material and support tissue maintenance. However, prolonged activation may contribute to an inflammatory environment that disrupts communication between nerve cells.

Chronic neuroinflammation may also affect mitochondrial function. Mitochondria are the energy powerhouses inside cells. Brain cells have particularly high energy requirements, so impaired mitochondrial function may influence their ability to communicate, repair and remain resilient.

As we can see, inflammation affects many different brain processes. It may influence energy production, the strength of connections between nerve cells, the integrity of the blood-brain barrier and the clearance of cellular waste. 

Blood vessel health provides another important link. High glucose, insulin resistance, elevated blood pressure and abnormal blood lipids can all affect the lining of the blood vessels. The brain requires a continuous supply of oxygen and nutrients. Damage to its larger or smaller blood vessels can reduce this supply and may contribute to strokes, small areas of tissue injury and vascular cognitive impairment.

Brain Fog and Energy Crashes
Blood glucose fluctuations can contribute to brain fog in some people. A meal or snack dominated by simple carbs can cause glucose to enter the bloodstream quickly. The body responds by releasing insulin. Glucose may then fall relatively rapidly, which can coincide with tiredness, hunger, irritability or difficulty concentrating. This is the familiar afternoon “crash” which can reflect what’s going on for you in your life - a combination of blood sugar imbalance, lack of protein, low hydration, too much caffeine and stress, or too little sleep. No wonder our brains don’t feel at their best! 

Average glucose is only part of the picture. HbA1c (which is often on GP blood tests) estimates average glucose exposure over the preceding two to three months, but it does not show every post-meal rise or fall. Researchers are increasingly interested in glucose variability, meaning the size and frequency of fluctuations throughout the day. Repeated large changes may contribute to oxidative stress and blood-vessel dysfunction, although the long-term significance of glucose variability in people without diabetes is not yet fully understood.

Responses to the same food can also vary. Meal composition, sleep, stress, activity, muscle mass, hormones and the order in which foods are eaten can all influence the glucose response. This is one reason why a single food should not automatically be labelled either good or bad for the brain.

Hormones, Stress and Sleep
Many women first become concerned about memory and concentration during perimenopause. Word-finding difficulties, forgetfulness and feeling mentally slower are commonly reported during this stage.

Changing oestrogen levels may affect brain signalling, temperature regulation, mood and sleep. At the same time, the menopause transition can be accompanied by changes in body composition and insulin sensitivity. These factors may overlap, making it difficult to attribute brain fog to one single cause.

Experiencing brain fog during perimenopause does not mean that somebody is developing dementia. However, symptoms that are new, persistent, worsening or interfering with daily activities should be discussed with a GP.

Sleep and stress can also influence both cognition and metabolic health. Even a single poor night’s sleep can affect attention and memory the following day. Repeated sleep disruption may reduce insulin sensitivity and increase inflammatory signalling.

Chronic stress can affect concentration directly, while stress hormones may alter glucose regulation and sleep quality. Blood sugar therefore cannot be considered in isolation from the wider circumstances in which symptoms occur.

If you’d like to find out more, why not book in a call?