The Brain You're Building: What We're Learning About Dementia Prevention

This article explains what actually influences your dementia risk, which prevention strategies have scientific backing, and how to build daily habits that protect your brain.

I keep a tin of sardines in my medical bag. Not for emergencies - though I suppose they could be - but because they're a surprisingly good conversation starter when someone asks about dementia prevention. People expect pills or supplements or elaborate protocols. They don't expect fish.

The 4 Primary Nutritional Drivers of Dementia Risk

Risk Factor	How It Damages the Brain	Dietary Sources to Address It	Optimal Target/Range
Excess Sugar	Damages blood vessels, creates inflammation, disrupts insulin signaling in brain cells (linked to "type 3 diabetes" theory of Alzheimer's)	Reduce refined carbohydrates, sugary beverages, processed foods; focus on whole foods with low glycemic impact	Keep blood glucose stable; HbA1c <5.7%
Omega-3 Deficiency	Brain is 60% fat (minus water); lacks DHA and EPA needed to build and maintain neuron structure and cell membranes	Fatty fish (sardines, salmon, mackerel, anchovies), fish oil supplements, algae-based omega-3s for vegetarians	Omega-3 Index >8%; 2-3 servings fatty fish weekly
B Vitamin Insufficiency	Elevated homocysteine levels damage blood vessels and brain tissue; impairs neurotransmitter synthesis and myelin maintenance	B12 (animal products, fortified foods), B6 (poultry, fish, chickpeas), Folate (leafy greens, legumes, fortified grains)	Homocysteine <7 µmol/L; adequate B12 >400 pg/mL
Chronic Inflammation	Accelerates neurodegeneration, damages blood-brain barrier, promotes amyloid plaque formation	Anti-inflammatory diet: colorful vegetables, berries, fatty fish, olive oil, nuts; avoid ultra-processed foods	Reduce inflammatory markers (hsCRP <1.0 mg/L)

But here's what we're learning, and it's both simpler and more complex than most people realize: two-thirds of dementia is Alzheimer's disease - a progressive shrinking of brain tissue that fundamentally isn't supposed to happen. This isn't age. This is biology gone wrong in specific, preventable ways.

And less than 1% of cases are purely genetic. Which means for the rest of us, the brain we have at 80 depends largely on what we've been doing - or not doing - for the preceding decades.

The Architecture of Brain Decline

The brain is 60% fat when you remove the water. That's not a metaphor. Your neurons, the cells that allow you to think and remember and recognize your children's faces, are built from fatty acids. Two specific ones, actually: DHA (docosahexaenoic acid - an omega-3 fatty acid found primarily in marine sources) and arachidonic acid (an omega-6 fatty acid derived from plants).

What's remarkable is this: every mammalian brain - from mice to elephants to dolphins to humans - has these same two fatty acids in roughly the same proportions. The size varies. The structure varies. But the fundamental building blocks don't. This was discovered in the 1970s by Professor Michael Crawford, who analyzed the fatty acid profiles of different organs across species and found that while livers and hearts varied wildly depending on diet, brains didn't. They couldn't. Evolution had locked in these requirements millions of years ago, back when our ancestors' brains were developing in an environment rich with these specific nutrients.

Which means you can't build a functional brain without them. And you can't maintain one either.

The Omega-3 Index: A Window Into Brain Health

We can measure this now. It's called the omega-3 index - the percentage of EPA (eicosapentaenoic acid) and DHA in your red blood cell membranes. Not floating around in your blood, but actually incorporated into the structure of the cells themselves. This matters because it reflects long-term status, not just what you ate last week.

And this number predicts things. Brain volume. Cognitive function. Future dementia risk. The correlation is almost linear. Lower omega-3 index, smaller brain density. Higher index, better cognitive performance. It's one of those rare findings in medicine where the relationship is clear enough to be unsettling.

Countries with higher fish consumption have lower rates of depression, suicide, and dementia. This isn't speculation - it's WHO data. You can actually predict a nation's mental health burden based on how much seafood its population eats. Inland populations, or those who avoid fish for religious or cultural reasons, show higher rates of cognitive decline.

Which brings us back to those sardines in my bag.

The Four Drivers of Brain Degeneration

If you're looking for a framework - and most people are, they want something to hold onto - there are four main nutritional factors that accelerate brain breakdown. I think of them as pressure points where modern life pushes hardest against our biology.

Sugar. Excessive glucose damages blood vessels, creates inflammation, and interferes with insulin signaling in the brain. Alzheimer's has been called "type 3 diabetes" by some researchers - a term that oversimplifies but captures something real about metabolic dysfunction in brain cells.

Brain fats. Specifically, the lack of omega-3s. This is the one that surprises people because fat has been demonized for so long. But your brain is fat. Depriving it of the right kinds is like trying to build a house with half the materials.

B vitamins. Especially B12, B6, and folate. These vitamins regulate homocysteine - an amino acid that, when elevated, damages blood vessels and brain tissue. Elevated homocysteine is a known risk factor for cognitive decline, and it's remarkably common, particularly in older adults or those on certain medications.

Antioxidants. Both the presence (from fruits and vegetables, particularly vitamin C and E) and the absence (smoking, air pollution, oxidative stress) matter here. Your brain uses 20% of your oxygen despite being only 2% of your body weight. That metabolic intensity generates free radicals - unstable molecules that damage cells - and without adequate antioxidant defense, that damage accumulates.

These aren't separate issues. They interact. Poor nutrition creates inflammation. Inflammation damages blood vessels. Damaged vessels reduce nutrient delivery to the brain. Reduced nutrient delivery accelerates cell death. It's a cascade, not a single failure point.

What Reversal Looks Like

There was a man - I'll call him Allan - who was diagnosed with mixed dementia. That's usually Alzheimer's (62% of dementia cases) plus vascular dementia (17%) - essentially brain shrinkage plus poor blood supply. His wife found him wandering their home at night, unable to locate the bathroom in the house where he'd lived for decades. He was a computer programmer who couldn't turn his computer on. A gardener who couldn't conceive of planting a garden because tomorrow was too abstract a concept.

The neurologist told them there was nothing to be done.

But his wife, Dorothy, found a different approach. She started him on omega-3 supplements. High-dose B vitamins. Eliminated sugar. He went ketogenic five days a week - forcing his brain to run on ketones (molecules produced when the body breaks down fat for energy) instead of glucose, which some research suggests may protect brain cells. He started sleeping an hour earlier every night. Sleep is when the brain clears metabolic waste - literally flushes out toxic proteins through the glymphatic system, a waste-clearance pathway discovered only in the last 15 years.

Within months, his cognitive function scores doubled. His dementia risk score - calculated from lifestyle factors - dropped from the high 50s (out of 100, where 100 is "doing everything wrong") to the low 30s. He planted his entire spring garden. He's back on email.

This isn't a cure. It's not magic. But it suggests that even diagnosed dementia isn't always a one-way street. The brain has more plasticity - more capacity to repair and compensate - than we used to think.

SMASH: The Practical Answer

If you want something actionable, memorize this: SMASH. Salmon, Mackerel, Anchovies, Sardines, Herring (or kippers). These are the fish highest in omega-3s, the ones that actually move the omega-3 index when you eat them regularly.

You don't need expensive supplements - though they work too - you need about two to three servings of these fish per week. That's the amount that consistently shows benefit in studies.

I mention this because people often overcomplicate prevention. They want elaborate protocols or expensive tests. But sometimes it's just: eat fish twice a week. Get seven hours of sleep. Walk daily. Eat vegetables. Limit sugar.

The barrier isn't knowledge. It's implementation. We know what works. The question is always: how do we make it happen in real life, with real constraints, real budgets, real schedules?

What We Don't Talk About Enough

Here's something I notice: people fear dementia more than almost any other condition. More than cancer, often. Because dementia doesn't just take your health - it takes your self. Your memories. Your personality. The thread that makes you, you.

But we don't talk about prevention the way we talk about, say, cardiovascular disease. Maybe because brain health feels more abstract. You can't see your brain. You can't feel plaque building up in your neurons the way you might feel chest pain or shortness of breath.

Or maybe it's because prevention requires changing things we're attached to: sugar, convenience, sedentary habits. And those changes feel like deprivation rather than investment.

But investment is what it is. You're building - or eroding - your future brain with every meal, every night of sleep, every walk you take or don't take.

The Limits of What We Know

I should say: not everything works for everyone. Allan's story is real, but it's also one story. Clinical trials show average effects across populations, not guarantees for individuals. Genetics matter - not just the rare causative genes but the common variants that influence how efficiently you absorb B vitamins or metabolize fats.

And timing matters. The earlier you start, the better. But even in your 60s or 70s, changes can help. The brain continues to form new connections - neuroplasticity - throughout life, though it becomes harder as we age.

There are also people who do everything right and still develop dementia. That's the hardest part to accept, both for patients and for doctors. Biology isn't perfectly predictable. But shifting odds in your favor is still worth doing.

What This Means for You

If you're reading this in your 30s or 40s, you're early enough that small changes compound dramatically over time. If you're reading it in your 60s or 70s, you're not too late - Allan proves that.

The omega-3 index can be measured from a simple blood test. Homocysteine too. These aren't standard panels, but they're increasingly available through functional medicine practitioners or direct-to-consumer labs.

But even without testing, you probably know if you're eating fish twice a week. You know if you're sleeping poorly. You know if your diet is mostly processed foods and sugar.

The question isn't really what to do. It's whether you'll do it.

The Larger Pattern

I think about this sometimes: how strange it is that we've created an environment so mismatched to our biology that basic brain health now requires conscious effort. Our ancestors didn't worry about omega-3 deficiency - they ate what was available, and what was available included fish and wild game rich in these fats.

We've built a food system that's convenient, shelf-stable, and cheap. But it's also nutritionally hollow in specific ways that matter for long-term brain function.

Which means prevention isn't just about individual choices. It's also about recognizing that we're swimming against a current. The default path - the path of least resistance - leads toward cognitive decline. Not because we're weak or lazy, but because the modern food environment is designed for profit, not health.

That's not a judgment. It's just reality. And knowing it means you can make different choices, consciously and deliberately, rather than drifting into patterns that don't serve you.

Some days I'm optimistic about this. Other days I wonder if we'll look back in 50 years and realize we created an entirely preventable epidemic of dementia through dietary choices that seemed harmless at the time.

But that's why this matters now. While we still have the chance to change course.