People with mentally stimulating jobs have a lower risk of dementia in later years than those who have non-stimulating work, research has suggested.
Scientists looked at more than 100,000 participants across studies from the UK, Europe and the US focused on links between work-related factors and chronic disease, disability and mortality.
The lead author said the latest findings support the idea that mental stimulation in adulthood could postpone the onset of dementia.
The study looked at a range of occupations, from civil servants to public sector employees and forestry workers.
While cognitive stimulation is already assumed to prevent or postpone the onset of dementia, until now trials have been based on fairly small sample sizes and short term-interventions, producing inconsistent results, researchers said.
They suggested a possible explanation for the conclusion in this large study is that cognitive stimulation is associated with lower levels of some proteins that might inhibit certain processes in the brain.
Cognitive stimulation at work was measured at the start of the study and those involved were tracked for an average of 17 years to see if they developed dementia.
Researchers said cognitively stimulating jobs include demanding tasks and high job decision latitude, also known as job control, whereas occupations seen as non-stimulating are those with low demands and lack of job control.
They said because such exposure to cognitive stimulation at work can take place over decades and add up to tens of thousands of hours, it lasts “considerably longer” than cognitive interventions or cognitively stimulating hobbies.
They found that the incidence of dementia was 4.8 per 10,000 person years in the high stimulation group, and 7.3 in the low stimulation group, having taken into account potentially influential factors including age, sex, educational attainment and lifestyle.
They made further adjustments for a range of established dementia risk factors in childhood and adulthood, and said the finding remained the same.
There was no difference between genders or those younger or older than 60, but there was an indication that the association was stronger for Alzheimer’s disease than other dementias.
Researchers acknowledged that the study is observational and so cannot establish cause, but they said the work’s main strength is the large sample size.
The study concluded: “This multicohort study of more than 100,000 participants suggests that people with cognitively stimulating jobs have a lower risk of dementia in old age than those with non-stimulating jobs.
“A possible mechanism for this association is the finding that cognitive stimulation is associated with lower levels of plasma proteins that might inhibit axonogenesis and synaptogenesis and increase dementia risk in old age.”
Lead author Professor Mika Kivimaki, from University College London’s Institute of Epidemiology and Healthcare, said: “Our findings support the hypothesis that mental stimulation in adulthood may postpone the onset of dementia.
“The levels of dementia at age 80 seen in people who experienced high levels of mental stimulation was observed at age 78.3 in those who had experienced low mental stimulation.
“This suggests the average delay in disease onset is about one and half years, but there is probably considerable variation in the effect between people.”
Prof Kivimaki said in the main analysis the data included a full range of occupations, but cognitive stimulation was measured using self-reports rather than occupations.
In a supplementary analysis, a job exposure matrix measurement was used for cognitive stimulation based on 87 different public-sector occupations.
Jobs with high cognitive stimulation included senior government officers, production and operations managers, directors and chief executives.
Occupations with low cognitive stimulation included cashiers, agricultural, fishery and related labourers, transport labourers and mobile-plant operators.
Dr Sara Imarisio, head of research at Alzheimer’s Research UK, said: “This large, robust study adds to a body of evidence suggesting that staying mentally active is important for helping reduce the risk of dementia.
“Previous research has suggested that keeping the brain active can help build cognitive reserve, a type of resilience that helps the brain ‘rewire’ its connections more easily and keep working for longer when diseases like Alzheimer’s take hold.
“This new research also identified proteins in people’s blood plasma that may be connected to this process, and further research should investigate this finding in more detail.
“Not everyone is able to choose the type of work they do, but studies like this highlight the importance of finding activities that help keep the brain active, whether it’s through work or hobbies.
“It’s not currently clear which activities are most helpful for building cognitive reserve, so whether it’s a stimulating job, reading or learning a language, finding something you enjoy is key.”