High mentally stimulating jobs may lower dementia risk later in life
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Results from a multicohort study of individuals in the U.S., U.K. and Europe revealed that people with high cognitively stimulating jobs were less likely to develop dementia in old age than those with low stimulating jobs.
“It was surprising to see such a clear association between mental stimulation in the workplace and dementia risk when previous studies on cognitively stimulating leisure activities and dementia have reported null findings,” Mika Kivimaki, PhD, a professor in the department of epidemiology and public health at University College London, told Healio Primary Care. “The explanation could be that exposure to cognitive stimulation at work typically lasts considerably longer than cognitively stimulating hobbies.”
Kivimaki and colleagues examined the association between cognitive stimulation from work and dementia risk in 107,896 participants enrolled in seven population-based prospective cohort studies.
Participants had no dementia at baseline, which ranged from 1986 to 2002. The researchers measured cognitive stimulation using standard questionnaires on active vs. passive jobs. Subsequent dementia diagnoses were identified through electronic health records and recorded clinical examinations. Follow-ups ranged in length from 13.7 to 30.1 years until 2017. Among the study cohorts, 58.2% were women and the mean age at baseline was 44.6 years.
A job was considered stimulating if it included cognitively demanding tasks and came with a high level of control over the work. Unstimulating jobs had low demands and a lack of control, according to Kivimaki. The researchers also evaluated self-reported education levels to determine a life course measure of cognitive stimulation. In addition, to identify potential biological pathways, they analyzed the association between cognitive stimulation and proteins in plasma among a random sample of 2,261 participants from a single cohort study, as well as the association between proteins and dementia risk in 13,656 participants from two cohort studies.
High vs. low mental stimulation
Among the participants, 27.1% had low, 47% had medium and 25.9% had high cognitive stimulation from work, according to the findings published in The BMJ. The incidence of dementia was 7.3 per 10,000 person-years among the low cognitive stimulation group compared with 4.8 per 10,000 person-years in the high cognitive stimulation group (HR = 0.77; 95% CI, 0.65-0.92). There was no significant difference in dementia risk between participants in the low and medium stimulation groups, according to the researchers.
Compared with a low education level and low cognitive stimulation at work, a high education level and high cognitive stimulation at work resulted in an HR of 0.63 (95% CI; 0.49-0.82), whereas a low education level and high cognitive stimulation at work yielded an HR of 0.8 (95% CI, 0.66-0.97) and a high education level and low cognitive stimulation at work yielded an HR of 0.73 (0.61-0.89), the researchers noted.
Kivimaki and colleagues said they found evidence that the association was stronger for Alzheimer’s disease than other dementias.
Proteins and dementia risk
In additional analyses, higher cognitive stimulation was “associated with lower levels of proteins that inhibit central nervous system axonogenesis and synaptogenesis,” the researchers wrote. They identified three proteins that appeared to be associated with an increased dementia risk: slit homologue 2, carbohydrate sulfotransferase 12 and peptidyl-glycine -amidating monooxygenase (P < .001 for all). The correlation “might provide clues to underlying biological mechanisms,” the researchers noted.
“This study linked mentally stimulating jobs to lower levels of proteins that prevent brain cells forming new connections and to a lower risk of dementia in old age,” Kivimaki said. “Staying mentally active may postpone dementia onset by about 1.5 years, but there is probably considerable variation in the effect between people.”
More research needed
In a related commentary, Serhiy Dekhtyar, PhD, an assistant professor in the Aging Research Center at Karolinska Institutet in Sweden, said that education is a key determinant of occupational attainment and likely influences cognitive enrichment.
“While the authors also report greater risk reduction in those with high education and low work stimulation (27%) than in those with low education and high work stimulation (20%), further pointing to education and not occupation as the key driver of prevention, they clearly show that cumulative exposure to both high education and high cognitive stimulation at work is associated with the greatest risk reduction of all (37%),” he wrote.
Dekhtyar noted that additional research is needed to confirm “whether educational and occupational stimulation truly help preserve cognition in old age, or if initial differences in cognitive ability underpin both engagement in mentally enriching environments and eventual risk of dementia.”
References:
Dekhtyar S. BMJ. 2021;doi: 10.1136/bmj.n1804.
Kivimaki M, et al. BMJ. 2021;doi:10.1136/bmj.n1804/.
Perspective
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Christian J. Camargo, MD
The concept of synaptic plasticity establishes a biological framework for the brain’s dynamic ability to alter the strength of connections between neurons. Within this framework, the more you learn, the more connections are physically represented in your brain. This connectivity may explain why people who have higher education or high professional achievement tend to be more resilient to cognitive decline. This resilience, cognitive reserve, is therefore modifiable, and something that anyone can work to develop. This study’s findings, that stimulating jobs are associated with lower dementia risk compared to non-stimulating jobs, may be related to this concept.
The seven cohort studies from which these data were drawn were European-based and designed to evaluate job strain and health outcomes. The authors determined the degree of stimulation at work based on a demand-control model of cognitive stimulation, in the form of a questionnaire which evaluates job demand and job control. They defined stimulating jobs (ie, active) as those with both high job demands and control. Conversely, non-stimulating jobs (ie, passive) had both low job demands and control. Stimulating jobs were associated with lower dementia risk even after adjustment for confounding variables. That the authors also found evidence of a biological mechanism makes these findings even more compelling.
However, there may be limitations regarding generalizability. How job demand and job control are perceived as high or low may vary outside of Europe. Additionally, demand and control fail to account for several other aspects of a job that can affect stimulation, eg location, coworkers, time off.
Ultimately, the finding that stimulating work environments are associated with favorable cognitive outcomes furthers current conventional thinking regarding strategies to slow cognitive decline and build cognitive reserve. Indeed, we often see the converse in the clinical setting, such as post-retirement when people may decline with the loss of work-based routine, interactions and cognitive stimulation. Future research may seek to better define the specific job characteristics most associated with cognitive benefit, subsequently evaluating their efficacy in a prospective, interventional study. Ideally, such work may lead to the identification of specific workplace modifications that anyone can implement.
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