Your brain doesn’t retire when you do—but it does have a few dealbreakers.

Last Tuesday, I watched my 84-year-old abuela teach my nephew how to play chess—every move calculated, every strategy passed down through generations of sharp minds. Her cognition was as precise as her opening gambit.

But just down the street, my neighbor struggles to remember his grandchildren’s names at 78.

The difference? The habits they’ve cultivated over a lifetime.

While genetics play a role in cognitive aging, our daily choices matter more than our DNA when it comes to staying mentally sharp.

The brain we have in our 80s is largely the product of the habits we practice today. Some patterns can fast-track cognitive decline, while others build resilience that lasts decades.

Here are seven habits that research shows can undermine your mental sharpness—and what to do instead.

1. Living in social isolation

“Loneliness kills. It’s as powerful as smoking or alcoholism,” says Robert Waldinger, director of the Harvard Study of Adult Development.

The research is clear: people who maintained strong social connections throughout their lives showed significantly less cognitive decline as they aged.

Think about it like this—your brain is like a muscle that needs regular workouts. Social interaction provides complex mental exercise.

When you’re chatting with friends, your brain juggles multiple tasks: processing speech, reading facial expressions, remembering shared experiences, and formulating responses. It’s like cognitive CrossFit.

The study showed that those who kept warm relationships got to live longer and happier, and the loners often died earlier.

Even more striking: people’s level of satisfaction with their relationships at age 50 was a better predictor of physical health than their cholesterol levels were.

The fix: Schedule regular coffee dates, join clubs based on your interests, or volunteer for causes you care about. The key is consistent, meaningful interaction with others.

2. Avoiding mental challenges

When we shy away from mental effort—puzzles that stump us, books that stretch us, conversations that challenge our perspective—we deny the brain the workout it needs.

As we age, this mental “coasting” can lead to earlier cognitive decline. But here’s the exciting part: your brain is far more adaptable than we once believed.

“New brain cell growth can happen even late into adulthood,” explains Dr. Ipsit Vahia from Harvard-affiliated McLean Hospital. “The process of learning and acquiring new information and experiences, like through structured classes, can stimulate that process.”

One study even found that older adults who took up complex skills—like digital photography or quilting—saw improvements in memory compared to peers who only engaged in passive activities.

It’s not just about staying busy; it’s about choosing challenges that stretch your capabilities and create new neural pathways.

The fix: Take up a new hobby that challenges multiple cognitive systems. Learn a language, master a musical instrument, or enroll in classes that genuinely stretch your mind.

3. Chronic stress without management

Stress hormones like cortisol are like acid rain on your brain. Short bursts are natural and even beneficial, but studies show that chronic stress literally shrinks brain tissue, particularly in areas responsible for memory and executive function.

The Harvard study found that people who developed healthy coping mechanisms for life’s ups and downs aged better cognitively. Those who learned to manage stress effectively maintained sharper minds well into their later years.

The fix: Develop a stress management toolkit. This might include meditation, regular exercise, journaling, or talking with a therapist. The key is having multiple strategies you can deploy when life gets overwhelming.

4. Neglecting quality sleep

Sleep is when your brain takes out the trash—literally.

During deep sleep, your brain’s glymphatic system washes away toxic proteins that can accumulate and contribute to cognitive decline. Skimp on sleep, and you’re essentially letting garbage pile up in your brain.

Poor sleep habits in midlife are strongly linked to cognitive problems decades later. It’s like compound interest, but in reverse.

The fix: Prioritize sleep hygiene. Create a consistent bedtime routine, keep your bedroom cool and dark, and avoid screens for at least an hour before bed. Aim for 7-9 hours of quality sleep each night.

5. Skipping regular exercise

Here’s what surprised me about exercise and the brain: it’s not just about blood flow.

Regular physical activity literally creates new brain cells, particularly in the hippocampus, the brain’s memory center. It’s like installing extra RAM in your computer.

Exercise also increases the production of brain-derived neurotrophic factor (BDNF), often called “Miracle-Gro for the brain.” This protein helps existing neurons survive and encourages the growth of new ones.

The fix: You don’t need to run marathons. Walking briskly for 30 minutes most days of the week can significantly boost cognitive function. Dancing, swimming, or even gardening counts. The key is consistency, not intensity.

6. Smoking and excessive alcohol consumption

The Harvard research was unambiguous: those who lived longer and enjoyed sound health avoided smoking and alcohol in excess.

Both habits accelerate brain aging by increasing inflammation and reducing blood flow to brain tissue.

Smoking damages blood vessels throughout your body, including those in your brain. Even moderate drinking can shrink brain tissue over time, particularly in areas responsible for decision-making and impulse control.

The fix: If you smoke, quit. If you drink, do so in moderation—no more than one drink per day for women, two for men. Seek support if you need it; quitting these habits is easier with community backing.

7. Mental passivity and routine rigidity

Your brain thrives on novelty and challenge. When you stick to the same routines day after day, year after year, you’re essentially putting your mind on autopilot. This mental passivity can accelerate cognitive decline.

The study also debunked the idea that people’s personalities “set like plaster” by age 30 and cannot be changed. Your brain remains plastic throughout your life, but only if you give it reasons to adapt and grow.

The fix: Shake up your routines regularly. Take a different route to work, try a new restaurant, read books outside your usual genre, or engage in activities that require you to think in new ways.

The compound effect of healthy habits

What makes the Harvard study so remarkable is its revelation that “the role of genetics and long-lived ancestors proved less important to longevity than the level of satisfaction with relationships in midlife.” Our choices compound over decades.

Think of brain health like tending a garden. You can’t plant seeds today and expect flowers tomorrow. But tend to your mental soil consistently—feed it with challenges, water it with social connection, give it the sunlight of new experiences—and you’ll harvest cognitive vitality for decades to come.

The beauty of neuroplasticity is that your brain remains changeable throughout your life. It’s never too late to start building better habits.

Your brain’s future starts today

As I write this, I’m reminded of my abuela’s hands, still steady as she moves her chess pieces, her mind still sharp as she navigates complex strategies with the wisdom of eight decades.

Her secret wasn’t just good genes—it was a lifetime of nourishing her brain with challenging activities, strong relationships, and the daily practice of staying curious about the world.

Your 80-year-old self is watching. What habits will you choose to cultivate today?