Individuals with cognitively stimulating jobs are at a lower risk of developing dementia than their peers with less challenging employment, new research suggests.
Results from a large, multicohort study also showed an association between cognitive stimulation and lower levels of certain plasma proteins, providing possible clues on a protective biological mechanism.
“These new findings support the hypothesis that mental stimulation in adulthood may postpone the onset of dementia,” Mika Kivimäki, PhD, professor and director of the Whitehall II Study, department of epidemiology, University College London, said in an interview.
The results were published online Aug. 19, 2021, in the BMJ.
‘Work fast and hard’
Researchers assessed the association between workplace cognitive stimulation and dementia incidence in seven cohorts that included almost 108,000 men and women (mean age, 44.6 years). All were free of dementia at baseline.
Participants included civil servants, public sector employees, forestry workers, and others from the general working population.
Investigators separated the participants into three categories of workplace cognitive stimulation: “high,” which referred to both high job demand and high job control; “low,” which referred to low demands and low control; and “medium,” which referred to all other combinations of job demand and job control.
“Highly cognitively stimulating jobs require you to work fast and hard, learn new things, be creative, and have a high level of skill,” said Dr. Kivimäki.
The researchers controlled for low education, hypertension, smoking, obesity, depression, physical inactivity, diabetes, low social contact, excessive alcohol consumption, and traumatic brain injury. These represent 10 of the 12 dementia risk factors named by the 2020 Lancet Commission on Dementia Prevention as having convincing evidence, Dr. Kivimäki noted.
Although the investigators had no data on the other two risk factors of hearing loss and air pollution, these are unlikely to be confounding factors, he said.
Follow-up for incident dementia varied from 13.7 to 30.1 years, depending on the cohort, and was 16.7 years in the total patient population. The mean age at dementia onset was 71.2 years.
Benefits across the life course
Results showed that incident dementia per 10,000 person years was 7.3 in the low–cognitive stimulation group and 4.8 in the high-stimulation group, for a difference of 2.5.
“These differences were relatively small because the incidence of dementia in this relatively young population was low,” Dr. Kivimäki said.
Compared with those with low stimulation, the adjusted hazard ratio for dementia for this with high stimulation was 0.77 (95% CI, 0.65-0.92).
The results were similar for men and women, and for those younger and older than 60 years. However, the link between workplace cognitive stimulation appeared stronger for Alzheimer’s disease than for other dementias.
There also appeared to be additive effects of higher cognitive stimulation in both childhood, as indicated by higher educational attainment, and adulthood, based on work characteristics, said Dr. Kivimäki.
“These findings support the benefits of cognitive stimulation across the life course, with education leading to higher peak cognitive performance and cognitive stimulation at work lowering age-related cognitive decline,” he added.
The findings don’t seem to be the result of workers with cognitive impairment remaining in unchallenging jobs, he noted. Separate analyses showed lower dementia incidence even when 10 years or more separated the assessment of cognitive stimulation and the dementia diagnosis.
“This suggests that the findings are unlikely to be biased due to reverse causation,” Dr. Kivimäki said.