We’ve probably all heard the phrase: “Use it or lose it” –  the belief that if we don’t keep our brains active, particularly as we grow older, our mental abilities will fade. Or that, conversely, if we stay mentally active we can hold back the inevitable decline that comes with ageing. But is that really true, and how might we differ from one another in this respect? A new study by Baowen Xue and colleagues from the RenEWL project at UCL tests the hypothesis.

If, as the theory goes, a lack of mentally challenging activity can lead to a loss of ability, then retirement might increase that risk. And previous studies suggest that may be the case – we know that those who retire later have better cognitive function and a lower risk of dementia.

In our study we set out to learn whether the sorts of activities we all do at work could benefit older peoples’ memories, and whether certain factors could help to preserve their abilities.  There’s a theory that some of us build up ‘reserves’ which can provide us with a buffer against later decline: if we have lots of mental stimulation as children, for instance, or if we have mentally demanding jobs as adults.

We wanted to test the ‘use it or lose it’ theory, and also to find out whether those who work in high-grade jobs might be at lower risk of cognitive decline after retirement.

The subjects for our research were 3433 people who participated in the Whitehall II Study, which followed a cohort of civil servants for more than 30 years, beginning when they were aged between 35 and 55.

Cognitive ability tests

We were able to look at measurements of the participants’ cognitive abilities from up to 14 years before they retired and for up to 14 years afterwards.

The participants were tested on four different measures. Their verbal memory was assessed through a test in which they listened to a list of words and were then given two minutes to write down as many as possible. Verbal fluency was judged in two ways – participants were asked to write as many words beginning with ‘S’ as they could within one minute – ‘phonemic’ fluency – and also to recall as many animal names as possible within the same time – ‘semantic’ fluency. Finally, abstract reasoning – the ability to identify patterns and rules in data and to use them to solve problems – was measured through a four-part test known as AH4.

We found that participants’ abilities decreased over time on all four measures.  But the decline in verbal memory scores was 38 per cent faster after retirement than it was before, even after taking account of that age-related deterioration. Those who worked in higher-grade jobs also had some protection while they were still working, but this effect was lost when they retired.

Trajectories of verbal memory by employment grade

However, while retirement had a significant impact on verbal memory, particularly for those in more senior jobs, it did not make a difference when it came to the other tests we looked at – verbal fluency and abstract reasoning. Nor were there any significant differences in verbal memory decline between men and women in our sample.

Our findings are consistent with the theory of ‘mental retirement’ – suggesting that the work environment can be more mentally stimulating than the leisure environment as a retiree. As well as losing the direct stimulation they get from work, retirees may also suffer from indirect effects – from losing the need for self-discipline and organisation, for example, as well as from having fewer opportunities to communicate and collaborate with others. For instance, social networks could be more extensive during employment than they are later in life.

The finding that employees in high grade jobs suffer smaller declines before retirement also points to a wider significance – all of us can benefit, in terms of memory, from mentally stimulating activities.

So, do our findings support the ‘use it or lose it’ theory? Yes, they do. They suggest that failing to keep mentally active may lead to faster cognitive decline after retirement.

Effect of retirement on cognitive function: the Whitehall II cohort study, by Baowen Xue, Dorina Cadar, Maria Fleischmann, Stephen Stansfeld, Ewan Carr,Mika Kivimäki, Anne McMunn and Jenny Head, is published in the European Journal of Epidemiology.