The Science Behind 'Use It or Lose It': Why Mental Engagement Matters More Than You Think

You've probably heard the phrase "use it or lose it" applied to everything from gym memberships to language skills. But when it comes to your brain, this familiar saying turns out to be backed by some remarkably powerful science, and the implications are more hopeful than most people realize.

If you've ever worried about cognitive decline, you're not alone. It's one of the most common concerns among adults over 55, and it makes sense. We notice when a name takes longer to retrieve or when we walk into a room and forget why. The good news? Your brain's trajectory is far less predetermined than you might think. The choices you make every day, what you read, learn, and engage with, matter enormously.

Let's look at what the science actually says.

A Landmark Study Confirms What We Hoped Was True

In March 2025, a major study published in Science Advances by Stanford economist Eric Hanushek and colleagues put the "use it or lose it" principle to a rigorous test [1]. Using longitudinal data from Germany's Programme for the International Assessment of Adult Competencies (PIAAC-L), researchers tracked the same individuals over 3.5 years. That's a meaningful improvement over earlier studies that simply compared different people at different ages.

What they found challenged a widespread assumption. Previous cross-sectional research had suggested that cognitive skills begin declining as early as age thirty. But when the researchers separated true age-related changes from generational differences and corrected for statistical artifacts, a different picture emerged.

Average cognitive skills actually increased into the forties before declining only modestly. And here's the key finding: among people who regularly used their cognitive skills, through work, hobbies, or continued learning, skills continued to increase even beyond their forties [1]. Decline wasn't inevitable. It was largely a consequence of disengagement.

Cognitive Reserve: Your Brain's Savings Account

If the Hanushek study tells us that engagement matters, the concept of cognitive reserve helps explain why. Think of cognitive reserve as a kind of savings account your brain builds over a lifetime. The more neural connections and pathways you develop through learning, problem-solving, and new experiences, the more backup routes your brain can call on when age-related changes occur.

A 2025 longitudinal study published in Aging Clinical and Experimental Research provided compelling evidence for this idea [6]. Researchers found that individuals with high cognitive reserve not only performed better at baseline but maintained a more stable cognitive state over time. Even among those who eventually developed a major neurocognitive disorder, people with high reserve preserved their cognitive profile significantly longer than those with low reserve [6].

The protective effect wasn't limited to early stages of aging. It buffered against decline even in more advanced stages. And the encouraging news? Cognitive reserve isn't fixed at birth. It's something you continue building through the activities and challenges you pursue throughout your life.

What Counts as "Using It"?

So what actually qualifies as mental engagement? The answer is broader than you might expect, and it goes well beyond crossword puzzles.

The Mayo Clinic Study of Aging followed 1,929 cognitively normal participants for an average of four years, tracking which activities were associated with reduced risk of developing mild cognitive impairment [2]. After adjusting for age, sex, and education level, the results were striking: computer use was associated with a 30 percent reduction in risk, craft activities with a 28 percent reduction, social activities with 23 percent, and playing games with 22 percent [2].

The results were published in JAMA Neurology, and one detail stands out: the protective benefits held even among carriers of the APOE ε4 gene, a known genetic risk factor for Alzheimer's disease [2].

One finding from this data deserves special attention: the 23 percent risk reduction associated with social activities. It's easy to overlook socializing as a form of cognitive exercise, but think about what a good conversation actually requires of your brain. You're listening, interpreting tone and meaning, retrieving relevant memories, formulating responses, reading body language, and navigating shifting topics, all in real time.

Research backs this up. A meta-analysis of longitudinal studies confirmed that consistent social participation is linked to slower cognitive decline regardless of other factors like depression or loneliness [10].

For many people, especially retirees, regular social connection may be the most accessible and enjoyable form of brain exercise available. A weekly card game, a walking group, regular visits with family and friends: these all count.

The common thread across all of these activities isn't any single type of mental exercise. It's active engagement, the kind that requires you to think, decide, create, or problem-solve. Reading a challenging book counts. So does learning a new recipe, having a spirited debate with friends, or working through a Sudoku puzzle or crossword. Passively watching television? Not so much.

The Retirement Risk: When Engagement Drops

One of the most revealing windows into the "use it or lose it" principle comes from studying what happens when daily mental demands suddenly disappear: retirement.

The Whitehall II study, a long-running British cohort study, tracked 3,433 civil servants with repeated cognitive assessments spanning up to 14 years before and 14 years after retirement [3]. The finding that caught researchers' attention: verbal memory declined 38 percent faster after retirement compared to before, even after accounting for normal age-related decline [3].

The effect wasn't uniform across all cognitive abilities, though. Abstract reasoning and verbal fluency were largely unaffected. It was verbal memory, the kind of recall most dependent on regular use and reinforcement, that suffered most [3]. The study also found that higher employment grade was protective against verbal memory decline while people were still working, but this advantage vanished after retirement.

This isn't an argument against retirement. It's an argument for being intentional about what fills your days afterward. The mental demands of work, deadlines, problem-solving, social interaction, learning new systems, don't have to disappear when the job does. They just need to be replaced with activities that are equally engaging.

What does that replacement look like in practice? Consider what your job actually demanded of your brain: managing schedules, communicating with colleagues, solving unexpected problems, keeping track of complex information. Now think about activities that exercise those same muscles.

Volunteering for an organization where you coordinate projects or mentor others. Taking a class, whether it's watercolor painting, a new language, or local history. Joining a discussion group or book club that pushes you to articulate your ideas. Even managing a household budget, planning travel, or learning to use new technology provides genuine cognitive challenge.

The goal isn't to replicate the stress of work, but to maintain the variety and regularity of mental demands that work naturally provided.

Your Brain Can Still Grow: Neuroplasticity After 55

There's another piece of this story that deserves attention: neuroplasticity, your brain's ability to physically reorganize itself by forming new connections throughout your entire life.

What does that actually look like inside your head? Your brain contains roughly 86 billion neurons, and they communicate through trillions of connections called synapses. When you learn something new, whether it's a language, a card game, or a route through an unfamiliar neighborhood, your neurons fire together in new patterns. With repetition, those connections strengthen. Unused pathways gradually weaken. This is the physical basis of "use it or lose it": your brain literally builds and reinforces the wiring it needs most.

For decades, most scientists believed the brain was essentially fixed by adulthood. We now know that's wrong. As Dr. Andrew Budson, Chief of Cognitive and Behavioral Neurology at the VA Boston Healthcare System and a Harvard Medical School faculty member, explains, neuroplasticity is "the brain's ability to learn, remember, and change when it is appropriate for the circumstances" [4]. And it doesn't have an expiration date.

Harvard Health research highlights that aerobic exercise triggers the release of brain growth factors that promote new neural connections, while activities like learning an instrument, painting, writing, or studying a new language actively strengthen cognitive function [4]. Mayo Clinic experts agree, noting that regularly stimulating your brain with puzzles and challenges, and building cognitive reserve through moderately challenging activities, is one of the best ways to take advantage of neuroplasticity as you age [5].

What triggers neuroplasticity most effectively? Three things: novelty, challenge, and practice. Every time you push yourself to learn something unfamiliar, your brain is literally rewiring itself, building new pathways and strengthening existing ones. That process doesn't stop at 55 or 65 or 85.

But What If I Haven't Been Doing This?

If you're reading this and thinking, "I wish I'd started years ago," here's the reassuring news: research suggests it's genuinely not too late. A randomized controlled trial published in Proceedings of the National Academy of Sciences found that healthy older adults who began a brain plasticity-based training program showed significant improvements in memory, and those gains were still measurable three months after the training ended [7]. What's more, participants' starting point didn't determine their ceiling. People who began with lower cognitive scores still showed meaningful improvement.

Neuroscientists studying aging and brain plasticity have found that the brain retains its capacity to change in response to experience well into late adulthood [8]. Your starting point doesn't limit your brain's ability to adapt. Whether you're 62 or 82, challenging yourself mentally can still make a measurable difference.

This doesn't mean you can undo decades of disengagement overnight. Building cognitive reserve is a gradual process. But the science is clear that starting today is always better than not starting at all, and the benefits can accumulate faster than you might expect.

How Much Mental Engagement Is Enough?

A natural question at this point: how often do you need to engage in mentally stimulating activities to see real benefits? The research offers some helpful guideposts.

A systematic review and meta-analysis of cognitive stimulation studies found that engaging in mentally challenging activities more than twice a week consistently produced better outcomes in memory, working memory, and attention compared to less frequent engagement [9]. That doesn't mean you need to dedicate hours every day. Sessions of around 45 minutes appear to be effective in structured programs, and at least ten sessions over time seem necessary for lasting results.

The key takeaway isn't a rigid prescription. It's that regularity matters more than intensity. A daily crossword puzzle, a weekly book club, a few hours of learning a new skill each week: these kinds of consistent, moderately challenging activities are what the research supports. The goal isn't to exhaust your brain. It's to keep it engaged, curious, and working on something that requires real thought.

The Science Is Clear, and It's in Your Favor

The research all points in the same direction: mental engagement isn't just a pleasant way to spend your time. It directly shapes the trajectory of your cognitive health.

You have more control over your brain's future than you may have been led to believe. The Hanushek study shows that continued skill use prevents decline. Cognitive reserve research demonstrates that the mental wealth you build today protects you tomorrow. And neuroplasticity confirms that your brain remains capable of growth and adaptation at every age.

The next step is simple: keep engaging. Whether that means picking up a new hobby, deepening a longtime interest, or making puzzles a daily habit, you're investing in your cognitive future every time you challenge your mind. If you're curious about how specific activities like crosswords, Sudoku, and word searches contribute to sharper thinking, take a look at our guide on how puzzles build processing speed as you age.

Your brain is ready to keep growing. The only question is what you'll teach it next.

References

1. Hanushek, E.A. et al. "Age and cognitive skills: Use it or lose it." Science Advances, 2025.
2. Mayo Clinic. "Mental activities may protect against mild cognitive impairment." Mayo Clinic News Network.
3. Xue, B. et al. "Effect of retirement on cognitive function: the Whitehall II cohort study." European Journal of Epidemiology, 2018.
4. Harvard Health Publishing. "Tips to leverage neuroplasticity to maintain cognitive fitness as you age."
5. Mayo Clinic Press. "The Power of Neuroplasticity: How Your Brain Adapts and Grows as You Age."
6. "Cognitive reserve can impact trajectories in ageing: a longitudinal study." Aging Clinical and Experimental Research, 2025.
7. Mahncke, H.W. et al. "Memory enhancement in healthy older adults using a brain plasticity-based training program: A randomized, controlled study." Proceedings of the National Academy of Sciences, 2006.
8. Park, D.C. and Bischof, G.N. "The aging mind: neuroplasticity in response to cognitive training." Dialogues in Clinical Neuroscience, 2013.
9. Gómez-Soria, I. et al. "Cognitive stimulation and cognitive results in older adults: A systematic review and meta-analysis." Archives of Gerontology and Geriatrics, 2022.
10. Piolatto, M. et al. "The effect of social relationships on cognitive decline in older adults: an updated systematic review and meta-analysis of longitudinal cohort studies." BMC Public Health, 2022.