Your brain is only as sharp as its
Brain fog, memory trouble, anxiety, migraines, the crash after COVID, the dementias of age: a surprising amount of it traces to one place, your brain’s smallest vessels and the blood moving through them. Here is what dims that supply, and what brings it back. Every claim sourced.
One supply line, under everything.
Lower the blood reaching the brain’s smallest vessels, or raise the inflammation running through them, and a brain that was coping starts to drift. It is the same wiring under conditions that look unrelated on paper, which is why one short list keeps turning up as treatment for all of them.
ADHD, autism and anxiety are dials, not switches. A diagnosis is a line drawn on a dial, and the shared pressures, less movement, more low-grade inflammation, and an infection almost everyone has now had, push people across it. The same things that restore blood flow carry them back.
How much are you working against?
Your brain runs on a margin, and the things below quietly spend it. Tick what applies to you and watch how much is left. Then see what each substance costs you.
Tap how many times you have had COVID, if any, then tick anything else that fits. This adds up one thing only, resting brain blood flow measured in imaging studies, not worth or blame. An ADHD or autistic brain is counted because it is perfused differently, not because it is a flaw. This is the trait itself, separate from prescribed ADHD medicine, which is a treatment that does not drain flow.
The per-factor figures come from brain-imaging studies and are sized conservatively, with the full sourcing below. The top bar stacks the resting blood-flow each factor costs, each one taken from the flow still left; the second runs higher because the brain has so little spare flow to spend that the cost to thinking outruns the raw drop in supply.
Where these come from
We sized each factor by how much it lowers resting cerebral blood flow in brain-imaging studies (ASL-MRI, SPECT, PET). Most are small on their own, and several are regional or only show up under stress. Where a finding is regional, we enter a reduced whole-brain-equivalent share rather than the larger regional figure. The sources:
- COVID: regional rather than whole-brain,1 so it stacks roughly with each infection; each one also carries an IQ-equivalent cost.2
- Smoking or vaping: lowers resting flow, though acute nicotine briefly pushes it the other way.3
- An ADHD brain, concentrated in the frontal regions.4
- Artery plaque or vessel disease: narrowing throttles the supply to the regions it feeds, and even silent plaque lowers flow.5
- Autism: concentrated in temporal and frontal regions; the whole-brain average reads normal, so we enter only a reduced whole-brain-equivalent of that regional shortfall.6
- Chronic inflammation: corrodes the vessel lining and the flow-matching system; higher long-term markers track a faster loss of regional flow.7
- Lower lung oxygen: small, because the brain widens its vessels to compensate.8
- Chronic poor sleep: clearest in sleep apnea.9
- POTS: close to normal at rest, with a sharp, temporary drop when you stand.10
Anxiety has no steady whole-brain percentage in this list: it shows a regional pattern rather than one number, and its sharpest forms, panic and standing, are already counted above through POTS.11 Anxiety has its own page.
Start where it bothers you.
What Hurts
COVID
What the infection does to the small vessels, and the vaccine question answered without a side.
Hormones
Where the brain fog comes from, and what the estrogen was quietly doing.
Substances & Sleep
Alcohol, nicotine, poor sleep and the daily habits that quietly drain the supply.
Concussion
Blood flow drops and the regulator fails, often after you already feel fine.
Aging
Vascular aging, dementia prevention, blood pressure, movement and the small vessels.
Anemia
Why thin blood starves the brain of oxygen even when the flow is fine, and the iron and B12 catches.
Symptoms
The Reserve
Why hard thinking and stress drain the brain, and the one mechanism under POTS, long COVID and the rest.
POTS/Standing
Dizzy or foggy when you stand. One mechanism under POTS, long COVID and ME/CFS.
Fainting
Why you black out, the common harmless faint, and the cardiac warning signs worth knowing.
Mental Health
When what gets called anxiety, panic or low mood is the body, briefly starved of blood.
Migraines
Why a falling barometer brings the pain, and the sensor in your ear that feels it.
Neurodivergence
ADHD and autism as dials, not switches, and what moves you along them.
Memory
Brain fog, the fragile hippocampus, and whether your memory is aging normally.
Keep your brain better supplied.
Most research on cerebral blood flow stays locked in journals, behind paywalls and jargon, far from the people it could help. The newsletter reads it for you and sends only what changes what you can do: a new way to raise your own blood flow, or a finding that moves the advice on this page.
The list is not open yet. It opens with the first issue. A few emails a year, every claim sourced.
Ten studies worth your time
If you read nothing else here, read these. Most are open access. Each title links straight to the study.
- Panic without a fear centre. Patients whose amygdala is destroyed feel no fear of outside threats, yet a lungful of CO2 still triggered full panic attacks, pointing to an alarm pathway in the body rather than the brain's fear centre.
- Same symptoms, different diagnosis. Shown identical filmed heart-attack symptoms, clinicians blamed a mental-health cause about twice as often when the patient was a woman, a controlled demonstration of bias rather than an anecdote.
- Told it was anxiety first. In a POTS patient survey, about 65 percent were told their symptoms were psychological and 45 percent were first diagnosed with anxiety.
- Training your way out of POTS. In a structured exercise programme, about 70 percent of patients who finished it no longer met the criteria for POTS, a hopeful result for a disorder usually framed as permanent.
- A wide perfusion gap. Brain imaging found women had higher blood flow than men in 67 of 68 regions, the largest sex difference in cerebral perfusion yet reported, which makes the abstract idea of brain blood flow concrete.
- The drop comes first. On standing, brain blood flow in POTS falls about 17 seconds before the racing heart and the sympathetic surge, marking low perfusion as the trigger rather than the result.
- Brain fog you can image. Arterial spin labeling MRI showed measurably lower cerebral blood flow in post-COVID patients with cognitive trouble, the most direct imaging evidence here that the symptom has a perfusion signature.
- Putting a number on it. A community study of roughly 113,000 people measured cognitive loss that scaled with severity: about 3 IQ-equivalent points after a mild infection that cleared, 6 with lingering symptoms, 9 after intensive care.
- Walking that rivals medication. A network meta-analysis found walking and running produced effects on depression comparable to antidepressants.
- Almost half is preventable. A standing Lancet commission estimates around 45 percent of dementia is potentially preventable through modifiable risks, with blood pressure and physical activity among them.