Your brain works only as well as its
Memory, focus, mood and sleep ride on the flow through the brain’s smallest vessels. COVID injures those vessels and lowers that flow, and by the end of 2023 almost 19 in 20 adults carried COVID antibodies, from infection or vaccination.1 One small-vessel injury now sits behind a wide spread of what gets treated as separate problems, from brain fog and attention to anxiety, low mood, broken sleep, migraine and the dementias. The largest study of post-COVID cognition measured the toll in points of IQ, scaling with how hard the infection hit.2 Those same vessels respond to what you do. That is what makes much of this preventable, and some of it reversible. Every claim sourced below.
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, anxiety and depression 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 caught COVID, then tick anything else that fits.
The per-factor figures come from brain-imaging studies and are sized conservatively; several are regional. 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 keeps little in reserve, so a small drop costs more of what is left.
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, so it stacks roughly with each infection;3 each one also carries an IQ-equivalent cost.2
- Smoking or vaping: lowers resting flow, though acute nicotine briefly pushes it the other way.4
- An ADHD brain, concentrated in the frontal regions.5
- Artery plaque or vessel disease: narrowing throttles the supply to the regions it feeds, and even silent plaque lowers flow.6
- Autism: concentrated in temporal and frontal regions, with whole-brain flow usually normal.7
- Chronic inflammation: corrodes the vessel lining and the flow-matching system; higher long-term markers track a faster loss of regional flow.8
- Lower lung oxygen: small, because the brain widens its vessels to compensate.9
- Chronic poor sleep: clearest in sleep apnea.10
- POTS: close to normal at rest, with a sharp, temporary drop when you stand.11
Anxiety has no steady whole-brain percentage in this list: it shows a regional pattern rather than one number, and its sharpest forms, panic over-breathing and standing, are already counted above through POTS.12 Anxiety has its own page.
Where to start.
COVID
What the infection does to the small vessels, and the vaccine answered without a side.
Standing Intolerance
Dizzy or foggy when you stand. One mechanism under POTS, long COVID and ME/CFS.
Aging Brain
Whether your memory is aging normally, and how much of dementia you can prevent.
Neurodivergence
ADHD and autism as dials, not switches, and what moves you along them.
Anxiety & mental health
When what gets called anxiety is the body, briefly starved of blood.
Migraines
Why a falling barometer brings the pain, and the sensor in your ear that feels it.
Concussion & TBI
Blood flow drops and the regulator fails, often after you already feel fine.
Menopause
Where the brain fog comes from, and what the estrogen was quietly doing.
What helps
The free, best-proven ways to get more blood to your brain.
Keep your brain better supplied.
Most research on cerebral blood flow never reaches the people it could help. We read it and send 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.
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 lasting drops in cognition and memory after COVID, with the largest deficits in those who had not recovered.
- 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 led by blood pressure and physical activity.