Have you ever walked into a room and completely forgotten why you went there? Or found yourself re-reading the same line in a book or email over and over again? Many women over 35 chalk this up to “just getting older.”
But here’s the truth: brain fog in your late 30s, 40s, and beyond isn’t simply a sign of aging. It’s often a reflection of shifting hormones, thyroid imbalances, blood sugar changes, and stress overload. There is good news: Once you understand the causes, you can take steps to clear the fog and restore your mental sharpness.
I personally had noticed my recall of words changing and a general brain fuzziness over the last few months. I chalked this up to due to my perimenopause shifting again (hopefully I’m on the home stretch!). These changes in my own brain function made me revisit this topic for myself, I thought i”d share it with you too.
Why Does Brain Fog Get Worse After 35?
Hormonal shifts play a central role. Estrogen supports brain function by boosting neurotransmitters like acetylcholine ( this is needed for learning and memory) and protecting mitochondria — these are the “batteries” inside brain cells which generate energy. When estrogen levels drop, energy levels in the brain declines, leading to memory slips and difficulty focusing.
But estrogen isn’t the only hormone at play. Progesterone also affects brain function. It acts as a calming influence and helps regulate something called the hypothalamic-pituitary-adrenal (HPA) axis, which governs your stress response. As progesterone declines in perimenopause, this stabilising effect weakens. This leaves women more prone to cortisol spikes, poor sleep, and a destabilised stress response — all of which contribute directly to brain fog.
Can Thyroid Issues Cause Brain Fog?
Yes. Thyroid hormones regulate metabolism in every cell, including brain cells. Even subtle changes in thyroid function ( even ones that may be dismissed as “normal”) can leave you feeling sluggish and foggy.
The most important Thyroid hormone to consider in this case is T3. This is the active form of thyroxine. Its our ‘Bang for Buck’ thyroid hormone that docks onto our cell’s outer membrane and signals the cell to start making energy. If T3 isn’t at optimal levels it may impact brain cell energy production, potentially making you feel foggy.
Insulin resistance: Why Brain fog hits after meals
If you notice brain fog after eating, especially carb-heavy meals, insulin resistance could be the culprit. Just like muscles, the brain can become resistant to insulin, making it harder for glucose (your main fuel) to get into cells.
This creates an “energy crisis” in the brain, particularly in regions responsible for focus and executive function. The result? That all-too-familiar afternoon crash. The Easy Remedy here is to balance out your meals. Ensure adequate amounts of Protein, fibre through non starchy vegetable and a little bit of healthy fats.
Does Stress and Cortisol Make Brain Fog Worse?
Absolutely. Chronic stress raises cortisol levels, which over time may shrink a part of the brain called the hippocampus. This is the brain’s memory center. High cortisol also interferes with sleep, robbing your brain of its nightly repair cycle. The combination of poor rest and chronic stress keeps your brain stuck in a foggy loop.
Neurotransmitters Affect Focus and Clarity
Hormonal changes in perimenopause alter brain chemistry. Serotonin and dopamine (linked to motivation, joy, and focus) naturally decline, while GABA (the neurotransmitter that calms and grounds you) becomes less effective.
This leaves many women feeling restless, unmotivated, overwhelmed and mentally drained.
What’s the Best Fuel for a Foggy Brain?
When the brain becomes insulin resistant, glucose isn’t used efficiently. That’s where ketones come in. Ketones are a cleaner, steadier energy source for the brain, which explains why some women feel sharper when reducing refined carbs or experimenting with intermittent fasting. Please note: you don’t need to do a strict Keto diet to generate ketones. I also don’t recommend long periods of fasting for every women, it can suit some but not all. More on this topic next blog post!
What Nutrients Can Help Clear Brain Fog?
While addressing hormones, thyroid, and lifestyle is essential, these are three of my favourtie nutrients that can provide extra support:
Magnesium Glycinate — Calms the nervous system, improves sleep, and regulates cortisol.
Omega-3s (especially DHA) — Essential for brain cell structure and reducing inflammation.
Creatine — Provides quick energy for brain cells; research shows it supports focus, mental stamina, and faster processing.
Final Thoughts: How Do You Beat Brain Fog After 35?
Brain fog is not “just aging.” It’s a signal that your body — and your brain — need support. By rebalancing hormones, checking thyroid health, managing blood sugar, and calming the stress response, you can restore clarity and feel like yourself again.
You deserve to feel sharp, focused, and energised — at every age.
I hope this helps. To learn more about my services, please book a discovery call via my booking link on home page of my website. This is a no obligation 20min chat to discuss your health goals and see if Naturopathy (and me!) are a good fit to help you feel your best.
