Watching a parent forget your name changes how you see your own future. Every lost word after fifty starts to feel like the first sign, and a quiet assumption settles in: it's in the genes, it's a lottery, and there's nothing to do but hope.
That assumption is wrong in a useful way. A large share of dementia is tied to things that can be changed, some of them decades before any symptom shows. And the one at the top of the list is a long way from crosswords, blueberries or brain-training apps.
Less of a lottery than it looks
Genes matter. One version of a gene called APOE raises the risk of Alzheimer's noticeably, and dementia can run in families. But genes load the dice more than they throw them.
The clearest proof came from a group of elderly nuns who agreed to donate their brains after death. Some of those brains were riddled with the plaques and tangles of Alzheimer's disease, yet the women had shown no sign of it in life. They'd kept teaching, writing and thinking clearly to the end. Their brains had enough spare capacity, built up over a lifetime, to keep working around the damage. That spare capacity has a name, cognitive reserve, and it's one of the things you can build.
Families share more than genes, too. They share the same food, the same habits, the same household products, the same air and water, often for decades, and that shared life explains part of why dementia runs in families. It's also the part you can change.
When the evidence on dementia was pulled together in 2024, nearly half of all cases worldwide were linked to fourteen things that can be changed across a lifetime, and the list is the same whatever your genes, which is why a gene test for Alzheimer's risk makes little practical difference. Some of the fourteen are obvious. The biggest one is a surprise.
Start with your ears
Hearing loss is at the top of the list. When your hearing fades, your brain works harder just to follow a conversation, pulling effort away from memory and thinking. Conversations get harder, so people join in less, and a quieter, more isolated life follows. The brain's hearing areas get less to do as well.
The encouraging part is that this one is easy to act on. When older adults at higher risk of decline were given hearing aids and support to use them, their thinking declined about half as fast over three years as that of similar people who got health advice instead. Hearing loss creeps up so slowly that you're usually the last to notice it. A hearing test is quick and painless, and the best time to have one is before you think you need it.
A hearing aid only helps if you wear it. Today's are small enough to disappear behind the ear or inside it, and in the US you can now buy them over the counter without a prescription. The benefit comes from wearing them every day, so a pair left in the drawer does nothing for your brain.
Then your eyes
Eyesight belongs on the list for similar reasons: less information reaching the brain, and a smaller, more careful life. Among older adults with cataracts, those who had the cataract removed developed dementia about 30 per cent less often over the following years than those who kept theirs, even after allowing for age, health and education. It's an association, and a striking one. If the world has been going dim or blurry, getting your eyes checked is worth doing for your brain as well as your reading.
Blood sugar and the brain
Your brain runs on a lot of energy, and it's sensitive to how that energy arrives. Years of high blood sugar damage the small blood vessels that feed the brain and blunt how brain cells respond to insulin. The link is strong enough that Alzheimer's is sometimes nicknamed "type 3 diabetes".
This matters even without diabetes. In people without it, those whose average blood sugar ran a little higher over five years had a higher risk of dementia than those whose levels ran lower, and the risk climbed step by step with the sugar. Keeping blood sugar low and steady, with fewer of the starches and sugars that spike it, is one of the most direct things you can do for your brain.
Keto and carnivore eating come in here. In the early stages of Alzheimer's, the brain gets worse at using glucose, sometimes years before memory slips, yet it keeps taking up ketones, the fuel the body makes from fat, as well as ever. Ketones can act as a back-up supply for a brain that's running short. When people with mild memory problems took a ketone-producing drink every day for six months, their memory and processing speed improved compared with a dummy drink. That drink was built on MCT fats, the kind in MCT oil, which the liver turns into ketones quickly. The groups are small and the work is early, but a diet that keeps blood sugar low and ketones available is aimed squarely at the brain's weakest point.
Blood pressure, the quiet one
High blood pressure in midlife is another item on the list, and it's easy to miss because it feels like nothing. Years of pressure stiffen and scar the small vessels deep in the brain, starving areas of it bit by bit. Knowing your numbers is easy: a at home, or a check at the pharmacy, will do it.
Heat may help too. Finnish men who took a sauna four to seven times a week had about a third of the dementia risk of those who went once a week, over twenty years of follow-up. It's an observation from a country that takes its saunas seriously, and a pleasant one to act on.
Move, and your memory centre grows
The memory centre of the brain shrinks a little every year after middle age. That seemed like a one-way street until older adults were asked to walk briskly for a year. On brain scans, their memory centres had grown by around two per cent, roughly winding back one to two years of age-related shrinkage, and their memory improved with it. The comparison group, who only stretched, kept shrinking.
A gym is optional. Brisk walking a few times a week, the kind that leaves you a little out of breath, was all it took, and a clipped to your belt makes it easy to keep count.
Sleep takes out the rubbish
During deep sleep, the brain clears away waste that builds up during the day, including beta-amyloid, the sticky protein that clumps into plaques in Alzheimer's. After a single night without sleep, healthy adults had measurably more of it in the brain regions that Alzheimer's tends to hit first.
One bad night is no disaster. Years of short or broken sleep are a different matter, and untreated sleep apnoea, where breathing stops and starts through the night, is a common hidden cause of broken sleep. Loud snoring and waking unrefreshed are the clues worth acting on.
Vitamin D, worth a blood test
Vitamin D is the dark horse. Among more than twelve thousand older adults followed for years, those taking vitamin D developed dementia about 40 per cent less often than those who took none. It's an observation, people who take vitamin D may differ in other ways too, and tests of vitamin D pills on memory have given mixed results. Low vitamin D is common, especially after a dark winter, and a blood test tells you where you stand; an at-home test kit does it from a finger-prick. Oily fish, egg yolks and liver supply some, and summer sun on bare skin supplies more.
Learn something hard
Crosswords and puzzle apps are pleasant, and if you're already good at them, they mostly exercise skills you already have. The brain builds reserve when it's pushed into something new and demanding.
When older adults spent three months learning digital photography or quilting, both new to them and properly difficult, their memory improved. Those who spent the same time on easy puzzles, films or social outings with no real challenge saw little change. A new language, an instrument, a trade, a sport with a steep learning curve: the harder it feels at first, the more it's likely doing.
London's cab drivers are the proof on a grand scale. To earn a licence they spend years learning "the Knowledge", some 25,000 streets and every landmark along them. Their memory centres grew as they learned, and when trainees were followed through it, those who qualified showed the growth while those who dropped out showed none. is full of stories like theirs, of brains that rewired themselves well into adulthood.
People and mood
Loneliness and depression both appear on the list. A social life keeps the brain busy with conversation, reading faces and keeping track of other people's stories, and it protects mood at the same time. Depression in midlife is linked with a higher risk later, which is one more reason to take a low mood seriously and get help early.
The rest of the list
The other items are familiar, and each one counts. Smoking damages blood vessels everywhere, including the brain. Heavy drinking does the same, and the risk rises with the amount. Head injuries matter, so wear the helmet on the bike and at the ski slope. Carrying a lot of extra weight around the middle, spending the day sitting, and breathing polluted air all add a little more. And years of schooling early in life build reserve that lasts, which is part of why learning anything new later still helps.
Two more deserve a place here, although they sit outside the official fourteen. The first is a group of everyday medicines: nightly use, over years, of the older drowsy antihistamines and the sleep aids that contain them, some bladder tablets and older antidepressants has been linked to a higher risk, which makes a long-standing sleeping tablet worth raising at your next medication review.
The second is your mouth. The bacterium behind gum disease has turned up in the brains of people with Alzheimer's, and its toxins track the disease; whether it helps cause it is still unproven, but brushing, flossing and dealing with gums that bleed is cheap insurance.
Better together, and later than you think
It's tempting to wonder whether any of this matters once you're past sixty. It does. When adults aged sixty to seventy-seven at raised risk spent two years improving their food, exercising, training their memory and keeping blood pressure and blood sugar in check, their thinking held up better than that of people given general health advice. Each change is modest on its own, and together they add up.
The pills sold for memory have a weaker record. Ginkgo, the best known of them, was given to more than three thousand older adults for around six years, and it did nothing to prevent dementia. The things on the list above cost less and do more.
When to get memory checked
Forgetting names and losing your keys are ordinary at any age. Worth checking are changes that interfere with daily life: getting lost on familiar routes, repeating the same question within minutes, struggling with bills or recipes you've managed for years, or family noticing a change before you do. The novelist Iris Murdoch is a haunting example. Her last book, written just before her Alzheimer's diagnosis, used a noticeably smaller and plainer vocabulary than her earlier novels. The change was there on the page before anyone saw it in her.
Get checked early, because some causes of memory trouble are fully reversible. Low vitamin B12, an underactive thyroid, depression, sleep apnoea and side effects from medicines can all look like the start of dementia, and all of them can be put right.
Sudden confusion is a different matter. Confusion that comes on over hours or days, especially in an older person, often points to an infection, dehydration or a new medicine, and it needs help the same day.
Start with the one nobody expects
Dementia is less of a lottery than it feels. Genes load the dice, and the rest of the table is yours: your ears, your eyes, your blood sugar and blood pressure, how much you move, how well you sleep, how hard you push your brain, and who you spend your time with. The nuns kept their minds in brains full of damage, carried by what they'd built up over a lifetime. That reserve is still yours to build, at forty or at seventy.
So start with the one nobody expects. Book a hearing test this month, even if you're sure your hearing is fine, then go for a brisk walk while you wait for the appointment. Your parent's story showed you what you're afraid of. What you do next shapes how much of it becomes yours.
Worried your forgetfulness is something more? Brain Fog: What Causes It, and What the Timing Tells You — the everyday causes of slow, foggy thinking, and how to tell them apart.
Want to know what to put on the plate for your brain? 8 Smart Ways to Fight Cognitive Decline with Food — the foods and eating habits linked to a healthier brain as you age.
Know someone who's convinced dementia is just in the genes? Send them this. The first thing worth doing might be a hearing test.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. If you or someone close to you is noticing memory changes that affect daily life, get checked early, since some causes are fully treatable.
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