The Perimenopause Pivot: Brain Fog
The 30% brain change nobody warned you about
“Mom has the memory of a goldfish these days.” – Nixon Killen, 2022
I was 47 when my daughter, Nixon, made a joke about my memory that sent me reeling - not because she meant anything mean by it, but because she was right. My memory WAS starting to flicker. I’d forget where I parked my car, why I walked into a room, or the plot of the last book I’d read.
I’m not alone. Up to 70% of women notice “brain fog” during perimenopause. But, you're not losing your mind; your brain is losing fuel.
The science behind what’s happening is both terrifying and oddly reassuring.
Terrifying because the data is dramatic. Reassuring because once you understand what's happening, you can do something about it.
The brain scan that changed how I think about menopause
Dr. Lisa Mosconi and her team at Weill Cornell published a study in PLoS One (2017) that should be required reading for every woman over 35. They used PET scans to measure glucose metabolism (basically, how much fuel your brain is burning) in healthy women ages 40 to 60 across three groups: premenopausal, perimenopausal, and postmenopausal.
The images are jaw-dropping. Premenopausal brains light up bright yellow and orange. Lots of activity. Lots of fuel being burned. Postmenopausal brains? Darker. Greener. Quieter…
With up to 30% less brain metabolic activity after the menopause transition.
Let that sink in. A healthy postmenopausal woman's brain can be burning 30% less fuel than a healthy premenopausal woman's brain. Same age range. Same education levels. Same general health. The difference? Menopausal status.
That's not aging. That's estrogen.
What estrogen was doing for your brain (that you never knew)
Your brain is an energy hog. It's only about 2% of your body weight but uses roughly 20% of your total energy. And estrogen was quietly managing that entire energy operation.
Estrogen regulates glucose transport into brain cells (fuel delivery). It supports mitochondrial function in neurons (the power plants that convert fuel to energy). It protects those mitochondria from oxidative damage. It promotes the production of acetylcholine, the neurotransmitter most closely tied to memory and focus. And it maintains synaptic plasticity, which is your brain's ability to form and strengthen connections.
When estrogen declines, it's not just one thing that goes wrong. It's the whole system. Less fuel getting in. Less efficient energy production. More oxidative damage. Fewer neurotransmitters. Weaker connections.
No wonder you can't find the word for refrigerator.
Why this matters beyond brain fog
Mosconi's research also showed that the brain regions most affected by menopausal metabolic decline are the same regions that deteriorate first in Alzheimer's disease. That pattern of hypometabolism in the PET scans? Researchers have seen it before. In early-stage Alzheimer's patients.
Two-thirds of Alzheimer's patients are women. And this research suggests the seeds may be planted during the menopause transition, decades before symptoms appear.
That's not meant to scare you. It's meant to motivate you. Because Mosconi herself says there's a critical window of opportunity in your 40s and 50s to intervene. The brain changes are real, but they're not inevitable.
Okay, but, what can you do about it?
Prescription-free HOP tips
Three buckets. Your brain will thank you for all of them.
The basics (that still matter)
Move. Exercise increases BDNF (brain-derived neurotrophic factor), which is basically Miracle-Gro for your neurons. It also increases blood flow to the brain and stimulates mitochondrial biogenesis in brain cells. Cardio and strength training both matter here.
Try the MIND diet approach. A hybrid of Mediterranean and DASH diets, specifically designed for brain health. One observational study shows it's associated with up to 53% reduced Alzheimer's risk. Key additions: berries (especially blueberries) and leafy greens, at least 6 servings per week.
Sleep. Your brain clears metabolic waste through the glymphatic system while you sleep. Skimp on sleep, and that waste accumulates. This one is non-negotiable for brain health.
The hidden levers
Learn something new. Novel learning builds new neural pathways and strengthens synaptic connections. A new language, instrument, or skill forces your brain to create fresh circuits. That's neuroplasticity in action, and it's available at any age.
Socialize. Real, face-to-face social interaction is one of the most potent cognitive stimulants we have. Isolation is a significant risk factor for cognitive decline. Your book club is brain medicine (as long as it doesn’t come with too much wine!).
The HOP Box play
NR (250mg). Your brain's energy crisis is fundamentally a NAD+ crisis. NR replenishes NAD+ to fuel neuronal mitochondria. If your brain is running on empty, this is the gas.
Magnesium glycinate (100mg). Regulates NMDA receptors, which control learning and memory. Also calms neuronal excitotoxicity (when brain cells get overstimulated and damaged). Most women are deficient.
B vitamins (B2, B6, B12, folate, TMG). The methylation squad. Methylation is essential for neurotransmitter production (serotonin, dopamine, norepinephrine) and for keeping homocysteine in check. Elevated homocysteine is a known risk factor for cognitive decline.
One more thing…
We’re a supplement company, not your prescriber. But the full perimenopause playbook often looks like this:
Hormone optimization therapy (talk to your doctor) + lifestyle levers + targeted supplementation.
That’s a powerful trifecta.
The bottom line
Brain fog during perimenopause is not a sign that you're broken. It's a sign that your brain is going through a massive energy transition. The estrogen that was running your brain's power grid for decades is stepping down, and every system it supported is feeling the shift.
But your brain is remarkably plastic. It can adapt, rebuild, and find new fuel sources. Move, feed it well, challenge it, and give it the raw materials it needs.
Thirty percent is a big number. But it's not a destiny. It's a starting point.
Now, HOP to it! 💪
Dr. Amy Killen & the HOP Team
P.S. My brain fog resolved when I made strategic changes to my lifestyle, supplements and hormone therapy. I still forget where I parked sometimes, but I’m chalking that up to an attention problem, not a brain energy problem. :)
References
Sex differences in Alzheimer risk: Brain imaging of endocrine vs chronologic aging
