Cognitive · Mental clarity
Brain fog
Brain fog is a symptom, not a diagnosis. It's a felt sense of mental slowness that can come from hormones, nutrients, thyroid, blood sugar, or sleep - and the combination matters more than any single number.
Feels like
Does this sound like you?
- Words on the tip of your tongue
- Losing the thread mid-sentence
- Reading the same page three times
- Slower at tasks that used to feel automatic
- A cotton-wool feeling when you try to focus
What to measure
The biomarkers that explain this symptom.
Grouped by the panel that tests them. We usually recommend running the top two panels together - patterns only show when you can see biomarkers next to each other.
Panel
thyroid
- TSH / Free T3Even high-normal TSH correlates with measurable cognitive slowing.
Panel
hormones
- EstradiolEstrogen is neuroprotective. Brain fog is often the first perimenopausal symptom.
Panel
nutrients
- Vitamin B12Required for myelin synthesis. Low B12 is a classic reversible brain fog cause.
Panel
metabolic
- Fasting Insulin / A1cInsulin resistance impairs neuronal glucose uptake - 'Type 3 diabetes' hypothesis.
Panel
cardio
- hs-CRPSystemic inflammation tracks with neuroinflammation and cognitive complaints.
Patterns we see
Three common clusters.
Your specific pattern will be unique, but most people land in one of these.
01
Perimenopausal
Estradiol variability + still-cycling. Brain fog worse pre-period.
02
Thyroid-adjacent
TSH 2.5+, borderline T3. Usually responds to nutrient optimization before meds.
03
Metabolic
Fasting insulin 10+, A1c 5.5+. Dietary intervention is first-line.
Ready to look?
Order the thyroid + hormones panels.
Running the top two panels together is what lets us see patterns. Add a third if you want a fuller picture - most people benefit from the trio.
Further reading
From our journal
Related symptoms