If you’re over 40 and finding that words slip away mid-sentence, names escape you or your focus is harder to hold, you’re not alone. Brain fog is one of the most common symptoms women report in perimenopause. It’s often mistaken for ageing, stress or even early cognitive decline, but in most cases it is a normal and reversible response to hormonal change.

How hormones shape brain function

Oestrogen is deeply involved in how the brain works. It supports neurotransmitters such as serotonin, dopamine and acetylcholine, which influence mood, memory, motivation and learning. As oestrogen levels fluctuate during perimenopause, these chemical messengers can drop too. The result is slower thinking, patchier recall and difficulty concentrating.

Progesterone plays an equally important role. It supports GABA, a neurotransmitter that calms the brain and helps you sleep deeply. When progesterone declines, sleep may become lighter and the body more reactive to stress. Many women describe a “wired but tired” feeling that can make brain fog feel more intense.

This is not a sign of permanent decline. It is your brain adapting to a new hormonal rhythm, and with the right support, clarity often returns.

Nutrition matters

The brain relies on nutrients to produce neurotransmitters and function effectively. Protein provides amino acids, the building blocks of serotonin and dopamine, and most women benefit from around 1.2–1.5 g per kg of bodyweight per day. Fibre is equally important. It slows glucose release to keep energy and concentration stable, supports beneficial gut bacteria that influence brain chemistry, and helps the body metabolise oestrogen more effectively.

Other key nutrients include zinc, magnesium and choline, which all support neurotransmitter production and nerve function. Slow-release carbohydrates, such as oats, beans and root vegetables, provide the brain’s preferred fuel: glucose.

The stress connection

Chronic stress adds another layer. High cortisol levels shift blood flow away from the prefrontal cortex, the part of the brain responsible for memory, planning and decision-making. At the same time, low progesterone reduces GABA activity, making sleep lighter and the mind more restless. Together, these changes amplify foggy thinking.

Daily practices such as breathwork, walking outdoors, gentle strength training, limiting stimulants and prioritising sleep help regulate cortisol and improve mental clarity.

Lifting the fog

Brain fog is not something you have to put up with. Small, consistent steps can make a real difference. Build meals around protein and fibre, add zinc- and magnesium-rich foods daily, and include slow-release carbohydrates. Prioritise restorative sleep and incorporate daily stress-reducing practices, even for ten minutes at a time.

Perimenopause is a time of transition, not decline. With the right support, your brain is fully capable of adapting — and the clarity you’re missing now can return.

If brain fog is affecting your quality of life, you do not have to figure it out alone. Claire O’Brien is a nutritional therapist specialising in gut and hormone health, she supports women through perimenopause with personalised nutrition, lifestyle strategies and hormone support.

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