As we get older, a few cognitive slip-ups might seem inevitable. But what’s become apparent over the past decade or so is that not everyone’s brain ages in the same way. Some people remain razor-sharp, even when their brains are riddled with the plaques associated with Alzheimer’s, while others notice significant cognitive decline after only modest damage.

The difference? A major factor is cognitive reserve – your brain’s ability to defend against ageing and adapt to damage. This cognitive buffer is heavily shaped by your lifestyle, behaviours and maybe even your mindset.

Now that we understand cognitive reserve better, researchers are increasingly focusing on how to strengthen it. And it turns out there are plenty of evidence-backed ways to build our neural defences – particularly at certain times of life.

The idea of cognitive reserve first emerged after Yaakov Stern at Columbia University in New York showed people with more education and a demanding job were less likely to get dementia. Over the years, it’s been revealed the brain we build for ourselves – through many different lifestyle factors – can account for differences in the degree of brain degeneration and its outcome on our mind.

While we loosely call this “cognitive reserve”, there are actually three types of reserve. “Brain reserve” is simply how big your brain is. If you assume cognition diminishes at some threshold of damage, then a bigger brain is going to succumb later. There’s also “cognitive reserve”, our brain’s dynamic ability to compensate in the face of atrophy. You might think of this as using a side route when the motorway is blocked. Finally, there’s “brain maintenance”, your brain’s ability to defend itself against disease.

The good news is, in addition to education, researchers have identified a number of lifestyle factors that can influence these crucial defenses against decline . “We now consider cognitive reserve as a dynamic property that continues to develop and thus gets shaped throughout life,” says Alvaro Pascual-Leone at Harvard Medical School.

One of the best-supported factors is bilingualism. Ellen Bialystok at York University in Canada, who first discovered the link between speaking a second language and increased cognitive reserve, recently showed bilingualism can delay dementia onset by four years. The mental effort of switching between languages, constantly suppressing one or the other, seems to give bilingual people greater neural flexibility – helping them use those side routes when the main road is damaged. The result is billinguals with Alzheimer’s show no difference in cognitive function compared to monolinguals, despite having greater atrophy in the brain. Last year, research also showed bilingualism helps preserve the hippocampus, a brain region involved in memory.

Another powerful activity is musical training. A study published in July showed older adults with musical training were better at discriminating speech in noisy environments than non-musicians. Brain scans showed why: unlike non-musicians, their brains weren’t having to recruit additional networks to perform the task, suggesting regular musical practice maintains neural architecture as people age.

But what if you only play occasionally? Studies suggest there may be a threshold effect in which playing an instrument with any frequency offers a modest cognitive benefit, but the real jump comes from playing for at least an hour most days.

Exercise too, is said to help, but evidence is mixed. In one study, researchers analysed 454 people’s brains post-mortem and found those who’d been most physically active two years before their death had better cognition despite the same amount of brain damage from Alzheimer’s, even controlling for the fact that cognitive decline reduced their ability to exercise. Exercise improves blood flow and increases protective brain chemicals, so it may contribute to brain maintenance – but more research is needed.

Is it ever too late to boost cognitive reserve?

For a long time, experts assumed cognitive reserve was largely set in childhood, and there’s some truth to this. “Without stimulation during childhood, a given pathway is less developed. If not used as adults, a pathway that was initially developed during childhood can become less efficient over time,” says Rhonda R. Voskuhl at the University of California, Los Angeles.

But now we know cognitive reserve continues to evolve across our life. Midlife may be a particularly valuable window of opportunity. Studies have shown people who stay mentally and physically active during their 40s and 50s – by reading, socialising, playing card games, learning musical instruments and similar – enjoy better cognition later in life. Importantly, these benefits are independent of early-life education or late-life activities, suggesting midlife offers a unique opportunity to contribute to your neural reserves.

And there’s no excuse to stop there – piano lessons in later life still protect against neurodegeneration, for instance. Even if you start to experience the decline you’re trying to avoid, there are still opportunities to build your reserves, says Pascual-Leone. “Individuals with early, mild cognitive problems due to Alzheimer’s disease can, and should, still work on enhancing their cognitive reserve, which will help reduce the risk of or delay the development of dementia,” he says. “It’s never too late.”

Lastly, while it’s easy to focus on physical activities that help cognitive reserves, emerging evidence suggests psychological traits may have an equally powerful role.

Take the feeling of purpose, for instance. People who have higher levels of purpose in life experience better cognitive function, despite similar levels of Alzheimer’s damage in the brain.

Similarly, a coherent mindset – the belief that life is comprehensible and manageable – also allows us to better tolerate a damaged brain. While the mechanisms remain unclear, some research suggests people with greater coherence use less brain activation when working on the same task compared to those with less coherence, hinting that they have enhanced neural efficiency.

The takeaway is you can’t change the brain you were born with, or the education you received early in life – but it’s never too late to change how it ages. It’s not necessarily easy: “What’s hard for the brain is good for the brain,” Bialystok tells me. But socialising, moving your body, learning a language, tickling the ivories and trying to find some purpose in life doesn’t seem like such a big ask – not for the prize of a sharper mind well into old age.

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