Perspective from Christian J. Camargo, MD
Disclosures: Dekhtyar reports no relevant financial disclosures. Kivimaki reports serving as a principal investigator for projects supported by external research funders, including NordForsk Nordic Research Programme on Health and Welfare, the U.K. Medical Research Council, the U.S. National Institute on Aging and the Wellcome Trust. Please see the study for all other authors’ relevant financial disclosures.
August 27, 2021
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High mentally stimulating jobs may lower dementia risk later in life

Perspective from Christian J. Camargo, MD
Disclosures: Dekhtyar reports no relevant financial disclosures. Kivimaki reports serving as a principal investigator for projects supported by external research funders, including NordForsk Nordic Research Programme on Health and Welfare, the U.K. Medical Research Council, the U.S. National Institute on Aging and the Wellcome Trust. Please see the study for all other authors’ relevant financial disclosures.
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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.”

Incidence of dementia per 10,000 person-years
Kivimaki M, et al. BMJ. 2021;doi:10.1136/bmj.n1804/.

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.

Mika Kivimaki

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/.