If you want to know which habits are bad for your brain, you’re in the right place. And I’ll warn you now: most of them are boring.
There’s no exotic toxin on this list. No single terrible decision. The things that wear a brain down tend to be small, repeated and completely normal. Another evening on the sofa. Another “quick” scroll that eats forty minutes. Another year of not getting that hearing test.
Boring cuts both ways, though. If ordinary habits can nudge your brain in the wrong direction, ordinary changes can nudge it back. You don’t need a biohacking budget. You need to notice what you’re doing on autopilot, then change one or two things.
Below are 16 habits worth quitting, each backed by research, most of it published in the last year or two. For every one you’ll get what’s going on, why it matters, and something concrete to do about it. If you’ve already worked through these 6 things to stop doing to become a better version of yourself, think of this as the brain-specific sequel.
1. Sitting for hours without a break
Most of us count workouts. Very few of us count sitting.
That’s a problem, because the two aren’t opposites. In a 2025 study in Alzheimer’s & Dementia, Marissa Gogniat (University of Pittsburgh), Angela Jefferson (Vanderbilt University Medical Center) and colleagues gave 404 adults aged 50 and over an activity-tracking watch for a week, then followed their brain scans and memory tests for seven years. People who spent more time sitting showed faster thinning of the hippocampus, a memory hub that’s among the first areas damaged in Alzheimer’s, and worse memory scores. The striking part: this held even among people who were physically active. Gogniat’s summary was that protecting your brain is “not just about working out once a day.” The effect was stronger in carriers of the APOE-e4 gene variant. It’s an observational study, so it can’t prove sitting causes the shrinkage. Early brain changes might also make people sit more.
Picture this: you run before work, feel virtuous, then sit for nine hours straight at a desk and three more on the sofa. On paper you’re “active.” Your hippocampus may not see it that way.
Start small: set a timer for every 45 minutes and stand, walk to refill water, or take a phone call on your feet. The goal is breaking up long stretches, not adding another workout.
2. Living on ultra-processed food
You probably know packaged snacks aren’t health food. What’s newer is how clearly they show up in brain data.
In a study published in June 2026 in the American Journal of Public Health, Harvard researchers followed 5,370 older adults from the US Health and Retirement Study for nearly nine years. According to Harvard Health’s June 2026 summary of the study, people who ate the most ultra-processed food had a 58% higher risk of developing dementia and a 46% higher risk of milder cognitive impairment than those who ate the least. Those who ate the most minimally processed food showed the reverse pattern, with a 41% lower dementia risk. The study can’t prove the food caused the difference, but ultra-processed diets are tied to obesity, diabetes, high blood pressure and high LDL cholesterol, all known risks for cognitive decline.
A separate 2026 study backs this up from another angle. Barbara Cardoso of Monash University and colleagues looked at more than 2,100 dementia-free Australians aged 40 to 70 and found that every 10% increase in the share of ultra-processed food in someone’s diet was linked to measurably worse attention, even in people whose diet was otherwise healthy (Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, April 2026). That one was cross-sectional, so it’s a snapshot rather than proof.
Cravings and tiredness make this harder than it sounds. If 8 p.m. is when your good intentions collapse, the problem may be decision fatigue as much as willpower, and these science-backed ways to overcome food cravings can help. Swap one ultra-processed item you eat daily, like a sugary drink or a deli-meat sandwich, for something closer to its original form, and keep that swap for a month.
3. Treating sleep as optional
Sleep is where a lot of quiet maintenance happens. Skimp on it and your brain may age faster.
A 2025 Karolinska Institutet study of 27,500 UK Biobank participants used brain MRI and machine learning to estimate how old each person’s brain looked. Researchers led by Abigail Dove scored sleep on five factors: chronotype, sleep duration, insomnia, snoring and daytime sleepiness. For every one-point drop in that healthy-sleep score, the gap between brain age and real age grew by about six months. People in the poor-sleep group had brains that looked roughly a year older than they were. Low-grade inflammation explained just over 10% of the link, which leaves room for other mechanisms, such as the brain’s waste-clearance system, which mostly runs during sleep. The study was published in eBioMedicine in October 2025. Its limits: sleep was self-reported, and UK Biobank volunteers are healthier than average.
A year of brain age might not sound dramatic. Remember it’s an average, and it’s built from habits most people treat as harmless, like snoring nobody checks or a bedtime that drifts later every month.
Next time, do this: pick a fixed wake-up time and keep it for two weeks, weekends included. If you’re dragging through afternoons anyway, these ways to fight sleepiness at work will help in the meantime, and if you snore loudly or wake up gasping, mention it to a doctor.
4. Pulling away from people when life gets heavy
When stress builds, a lot of us do the same thing. We cancel.
The American Psychological Association’s Stress in America 2025 survey, run by The Harris Poll among 3,199 US adults in August 2025 and released in November, found that 62% named societal division as a significant source of stress. About half reported loneliness: 54% said they felt isolated, 50% felt left out and 50% said they lacked companionship. People stressed by division were also more likely to cancel plans (55% versus 37%). And 69% said they’d needed more emotional support in the past year than they got.
Why does that matter for your brain? The largest meta-analysis on the question, by Martina Luchetti, Angelina Sutin and colleagues at Florida State University (Nature Mental Health, October 2024), pooled data from 608,561 people across 21 samples and found that loneliness was linked to a 31% higher risk of dementia. The association held after accounting for depression and social isolation. It’s correlational, and the studies measured loneliness in different ways, but the pattern is consistent.
Being alone isn’t the problem, by the way. Plenty of people enjoy solitude and are perfectly well connected. Loneliness is the gap between the contact you have and the contact you want.
Your move: next time you’re about to cancel, shrink the plan instead. Coffee instead of dinner, a walk instead of a party. If conversations themselves feel like hard work, these tips on how to improve social skills are a good place to begin.
5. Feeding yourself a steady diet of short videos
Reels, Shorts, TikTok. Thirty seconds at a time, two hours by the end of the night.
In September 2025, Lan Nguyen and colleagues at Griffith University published a meta-analysis in Psychological Bulletin covering 71 studies and 98,299 people. Heavier short-form video use was associated with poorer cognition overall (a moderate correlation, r = −.34). The strongest links were with attention (−.38) and inhibitory control (−.41), which is your ability to stop yourself acting on an impulse. Interestingly, compulsive, hard-to-stop use was more strongly linked to poorer cognition than plain hours watched. Most of the included studies were cross-sectional, so the arrow could point both ways: people who already struggle with focus might gravitate to quick videos.
Still, attention is a trainable skill. Anything that drills your brain to expect a new reward every few seconds makes sustained focus harder to reach. If you’ve been chasing deep work lately, getting into the flow state is hard to do with a feed one thumb-swipe away.
Test it this week: turn off autoplay, and only watch short videos sitting down at a set time, never in bed and never “while waiting.” Notice how often you reach for the app out of habit rather than interest.
6. Keeping the internet in your pocket every waking minute
Here’s how always-on access wears you down, step by step. Your phone offers something new every time you look at it. So you check it in every gap: queues, ad breaks, the half-second before a meeting starts. Each check pulls attention away from whatever you were doing. And because the phone fills every gap, it quietly pushes out the things that refill you, like talking to someone in person, moving or being outside.
That last link is the important one, and it was tested directly. In a randomized trial published in PNAS Nexus in February 2025, Noah Castelo (University of Alberta) and colleagues had 467 adults block all mobile internet on their phones for two weeks, while calls and texts still worked. Daily screen time fell from an average of 314 to 161 minutes. Sustained attention improved by an amount equal to roughly ten years of typical age-related decline, and mental health and well-being improved too. A mediation analysis suggested the gains came partly from how people spent the freed-up time: more in-person socializing, exercise and time in nature. So the trial supports a causal effect on short-term attention and mood. Limits: only about a quarter of participants managed the full two weeks, and they knew what the study was about.
A quick experiment: for the next seven days, switch off mobile data from 8 p.m. until morning. If it feels uncomfortable, that’s useful information about how much the phone runs your evenings. Reading up on how to stop living on autopilot can help you decide what to put in its place.
7. Letting AI do your thinking for you
AI tools are useful. The trouble starts when they do the part of the job your brain was supposed to do.
At the MIT Media Lab, Nataliya Kosmyna and colleagues recorded the brain activity of 54 students aged 18 to 39 with EEG while they wrote essays under three conditions: using ChatGPT, using a search engine, or using nothing at all. The brain-only group showed the strongest, most widespread connectivity. ChatGPT users showed the weakest. When the ChatGPT group later had to write without it, they were under-engaged and struggled to recall what they’d written. The researchers call this “cognitive debt,” and Kosmyna has put it bluntly: “There is no cognitive credit card” (ODSC interview, August 2025). Treat this with caution. The paper is a preprint that hadn’t been peer-reviewed (first posted June 2025, revised December 2025), the sample was small, and it tested one task.
Think of a gym spotter who lifts the bar every time it gets heavy. You’ll finish your sets, but your muscles never carry the load, so they don’t adapt. The comparison breaks down in one useful way: in the MIT study, people who wrote on their own first and only then used ChatGPT did well, with stronger recall. The tool hurt most when it replaced effort instead of following it.
So write your own first draft, outline or answer before you ask an AI to improve it, and when you need to remember something long term, try these science-backed memory methods rather than outsourcing it.
8. Telling yourself it’s too late to quit smoking
Smokers in midlife often assume the damage is done. Recent data says otherwise.
In October 2025, Mikaela Bloomberg, Andrew Steptoe and colleagues at University College London published an analysis in The Lancet Healthy Longevity using long-running surveys of older adults in England, the US and ten other European countries. They compared 4,718 people who quit smoking with an equal number of matched people who kept going, 9,436 in total, average age 58. Before quitting, both groups’ memory and verbal fluency scores declined at the same rate. In the six years after quitting, the quitters’ memory declined about 20% more slowly and their verbal fluency about 50% more slowly. That’s observational, so unmeasured differences between quitters and non-quitters can’t be ruled out. But the matching and the similar trends before quitting make the finding harder to dismiss.
Here’s a simple way in: set a quit date within the next two weeks and tell one person about it. Then ask your doctor or a local stop-smoking service what support is available to you, so the date isn’t resting on willpower alone.
9. Drinking more than you think you do
Most people underestimate their drinking. A glass with dinner, a few on Friday, a bottle shared at the weekend. It adds up to “heavy” faster than you’d expect.
A 2025 study in Neurology by Alberto Fernando Oliveira Justo and colleagues at the University of São Paulo examined the brains of 1,781 people who’d died at an average age of 75, then compared what they found with drinking histories reported by family members. Heavy drinking was defined as eight or more drinks a week. Here’s how often small-vessel brain lesions showed up:
| Drinking history | Had vascular brain lesions |
|---|---|
| Never drank | 40% |
| Moderate drinkers | 45% |
| Heavy drinkers | 44% |
| Former heavy drinkers | 50% |
After adjusting for age at death, smoking, physical activity and other factors, heavy drinkers had 133% higher odds of these lesions than people who never drank. Former heavy drinkers had 89% higher odds and moderate drinkers 60%. Heavy drinkers also had higher odds of tau tangles, a marker linked to Alzheimer’s, and died on average 13 years earlier. It’s an association, not proof of cause, and drinking was reported by relatives after death.
Leana Wen, an emergency physician at George Washington University, said in April 2025 that the lasting damage in former heavy drinkers stood out, though stopping still appeared to lower risk.
Give it a go: count every drink for two normal weeks, honestly. If your weekly total regularly hits eight or more, pick two alcohol-free days per week as a first step.
10. Blasting your headphones and ignoring muffled hearing
Hearing feels like an ear problem. It’s also a brain problem.
The World Health Organization’s World Hearing Day 2025 materials warn that more than 1 billion young people are at risk of permanent hearing loss from unsafe listening, mainly loud music through headphones and loud gaming, and that over 500 million people worldwide are expected to have disabling hearing loss requiring rehabilitation by 2030.
The brain link shows up later in life. In a research letter in JAMA Neurology (August 2025), Lily Francis, Sudha Seshadri and colleagues followed 2,953 participants of the Framingham Heart Study for up to 20 years. Among people whose hearing loss was diagnosed before age 70, those who used hearing aids had a 61% lower risk of dementia than those who didn’t. After 70, no such link appeared. Yet only about 17% of people with moderate-to-severe hearing loss use hearing aids, the authors noted. The study is observational, and hearing-aid users may simply have better access to healthcare overall.
Your move: turn your headphone volume to a level where you could still hear someone speaking next to you, and use your phone’s built-in sound-level warnings. If people seem to mumble more than they used to, book a hearing test instead of waiting.
11. Not knowing your blood pressure
High blood pressure doesn’t hurt. That’s exactly why it gets ignored.
This is one of the few habits on the list with strong causal evidence. Jiang He (UT Southwestern Medical Center), Yingxian Sun (China Medical University) and colleagues ran a cluster-randomized trial in 326 villages in rural China involving 33,995 people aged 40 and over with uncontrolled high blood pressure (Nature Medicine, April 2025). In half the villages, trained community health workers adjusted medication to reach a target below 130/80 mm Hg, with doctors supervising. Over 48 months, blood pressure in that group fell by 22.0/9.3 mm Hg more than under usual care. All-cause dementia was 15% lower, and cognitive impairment without dementia was 16% lower. Serious adverse events were less frequent too. Because villages were randomly assigned, this is evidence of cause and effect rather than a mere correlation, though the setting (rural China, mostly untreated patients) may not match yours exactly.
Get your blood pressure measured this month, at a pharmacy, a GP practice or with a validated home monitor. If it’s high, ask your doctor about a treatment target and how often to recheck.
12. Brushing off a long stretch of low confidence and poor coping
Everyone has a rough patch. The worry is a rough patch that quietly becomes the new normal.
A study in The Lancet Psychiatry (December 2025) by Philipp Frank, Mika Kivimäki, Gill Livingston and colleagues at UCL used data from 5,811 middle-aged civil servants in the Whitehall II study. Their depressive symptoms were measured in 1997 to 1999, and they were followed for about 23 years. In that time, 10.1% developed dementia. People with five or more depressive symptoms had a 27% higher dementia risk. But in those under 60, the risk was driven entirely by six specific symptoms, including losing confidence in yourself, difficulty facing or solving problems, and reduced warmth and affection toward others. Losing confidence and difficulty coping were each linked to about a 50% higher risk. Low mood itself and sleep problems weren’t. The sample was 72% male and 92% white, and these symptoms may partly be early signs of brain change rather than causes.
Either way, the practical conclusion is the same. These are symptoms that deserve attention, not a stiff upper lip.
Start small: if you’ve felt less capable and more withdrawn for more than a few weeks, tell your doctor in those exact words. Meanwhile, if your mind keeps looping on the same worries, these ways to stop ruminating thoughts can take some pressure off.
13. Walking and exercising along busy roads
You can’t control the air in your city. You can control where you breathe hardest.
A 2025 meta-analysis led by researchers at the MRC Epidemiology Unit, University of Cambridge (Clare Rogowski, Christiaan Bredell, Haneen Khreis and colleagues, The Lancet Planetary Health, July 2025) pooled 51 studies covering more than 29 million people. For every 10 micrograms per cubic metre of fine particulate matter (PM2.5), the relative risk of dementia rose by 17%. For every 1 microgram of soot, which comes largely from vehicle exhaust and wood burning, it rose by 13%. For context, the average roadside PM2.5 reading in central London in 2023 was about 10 micrograms. Most of the data came from high-income countries and white populations.
The proposed mechanism goes like this. Fine particles are small enough to get deep into the lungs and into circulation. From there, they’re thought to trigger inflammation and oxidative stress, a chemical process that damages cells, proteins and DNA. Both processes play an established role in how dementia starts and progresses. The researchers describe this as a plausible pathway rather than a proven chain.
Next time, do this: plan your run, cycle or daily walk along a park, river or side street instead of the main road, and check an air-quality app before outdoor exercise on still, smoggy days.
14. Being careless with your head
Helmets feel like a kid thing. Rugs, stairs and wet bathroom floors feel harmless. They’re not.
In October 2025, Jenny Yu Qing Huang and colleagues at the University of Toronto published an analysis in the Canadian Medical Association Journal of more than 260,000 people aged 65 and over in Ontario. A new traumatic brain injury was associated with a 69% higher risk of dementia within five years, and a 56% higher risk after that. People with a recent brain injury were also 30% more likely to need home care and 45% more likely to move into long-term care. More than half of brain injuries in older adults come from falls.
Why would a knock to the head echo years later? When you hit your head or get violently jolted, the brain can strike the inside of the skull and sustain damage. Not every injury leads to dementia, and the study shows association rather than proof. But head injury is one of the few dementia risks you can reduce with very simple equipment.
A quick experiment: walk through your home tonight looking only for trip hazards (loose rugs, cables, dark stairs) and fix one. Then make the helmet non-negotiable for cycling, scooters and skiing.
15. Assuming you need 10,000 steps or it doesn’t count
All-or-nothing thinking is sneaky. If 10,000 steps feels impossible, why bother with 4,000?
Melody Ding, a public health professor at the University of Sydney, has pushed back on that target directly. She told the BBC in July 2025 that the 10,000-step goal is “not evidence based.” Her team’s 2025 analysis puts the useful threshold much lower.
In their meta-analysis in The Lancet Public Health (July 2025), Ding and colleagues pooled 57 studies from 35 cohorts, including roughly 160,000 adults whose steps were measured with devices. Compared with 2,000 steps a day, 7,000 steps was associated with a 38% lower risk of dementia and a 22% lower risk of depressive symptoms. Going up to 10,000 added only a small extra reduction for dementia. The authors flagged that fewer studies covered dementia than outcomes like mortality, so certainty there is lower.
The message for your brain is encouraging. Going from very little to moderate movement seems to matter more than chasing a big round number, and these good habits to have in life show how small routines like this tend to stick.
Test it this week: check your phone’s step history for the past seven days, find your average, and add 1,000 steps a day to it. One extra walk after lunch usually covers it.
16. Treating brain health as a problem for later
Most people file dementia under “old age.” The research files it under “midlife.”
The 2024 report of the Lancet Commission on dementia prevention, intervention and care, written by 27 experts led by Gill Livingston, identified 14 potentially modifiable risk factors across life, including physical inactivity, smoking, excess alcohol, hearing loss, high blood pressure, high LDL cholesterol, depression, social isolation, head injury and air pollution. Their estimate: about 45% of dementia cases could theoretically be prevented or delayed if all 14 were eliminated. That figure assumes the risk factors are causal and fully removable, so treat it as a ceiling, not a promise. The commission also places several of these risks, high LDL cholesterol among them, in midlife, long before memory problems usually show.
Does acting on them work? The U.S. POINTER trial, published in JAMA in July 2025, randomly assigned 2,111 older adults at risk of cognitive decline to one of two lifestyle programs for two years. Both covered exercise, the MIND diet, mental and social challenge, and health monitoring. Both groups improved on cognitive tests, and the more structured, coached program improved more.
If you’re in your twenties or thirties, this is one more reason to invest in yourself in your 20s with health habits as well as skills. At any age, book one check this year that you’ve been putting off, whether that’s blood pressure, cholesterol, hearing or eyes, and pick a single habit from this list to work on first.
What to do when you slip
You will slip. Everyone does. The question is what happens the day after.
A systematic review by Ben Singh and colleagues at the University of South Australia (Healthcare, December 2024) looked at 20 studies with 2,601 participants trying to build healthy habits. The studies that measured timing found that habits took a median of 59 to 66 days to form, with individual estimates ranging from 4 to 335 days. That’s a lot longer than the “21 days” myth. Singh’s advice was to focus on consistency rather than perfection: missing a day doesn’t count as failure, as long as you pick the habit up again the next day.
The research in this article backs that up in a different way. Quitting smoking was linked to slower memory decline even in people who quit in their fifties or later. Stopping heavy drinking appeared to lower risk. And in U.S. POINTER, even the lighter, self-guided program improved cognition. The study’s principal investigator, Laura Baker of Wake Forest University School of Medicine, said that even modest changes may protect the brain.
So when a bad week happens:
- Restart at the smallest possible version. One walk, one early night, one alcohol-free evening.
- Look for the trigger. Was it stress, tiredness, a particular place, a particular person, or simply a week where everything ran late and the easy option was the only one left?
- Don’t add punishment. Skipping dinner to “make up” for takeaway or doing a brutal workout to cancel out a lazy week tends to backfire.
If you notice a pattern of undoing your own progress every time things go well, these signs of self-sabotage are worth a read. And for the day itself, here’s how to get over a bad day without writing off the whole week.
Conclusion
None of these habits will wreck your brain overnight. That’s what makes them easy to ignore, and also what makes them fixable. Small, repeated choices built the problem, and small, repeated choices can work against it.
You don’t need to tackle all 16. Pick the one that made you wince a little, the one you recognized instantly, and start there this week. Then come back in two months and pick the next one.
For more practical, research-backed ideas on building better habits, browse our Self Improvement section.
