- More than 50 million people live with dementia around the world.
- Scientists are interested in determining whether cognitive stimulation may protect against dementia.
- Previous studies have largely been inconclusive, producing little evidence to link staying mentally active during leisure time to protection against dementia.
- The researchers behind the present study looked at cognitively stimulating jobs and found that people with such lines of work had a 23% lower risk of dementia than other people.
Researchers have found that people who have more mentally stimulating jobs have a significantly lower risk of developing dementia later in life. This finding has led them to conclude that such cognitive stimulation could postpone the onset of symptoms.
The findings emerged from a large, cohort observational study, which the BMJ recently published.
The researchers also found an association between cognitively stimulating jobs and reduced levels of particular proteins that can increase the risk of dementia. This association, the researchers believe, may suggest that an underlying biological mechanism accounts for the link between mentally stimulating jobs and a lower risk of dementia.
Risk factors for dementia
According to the Centers for Disease Control and Prevention (CDC), dementia causes various symptoms that affect daily life, such as difficulty remembering, thinking, or making decisions.
The World Health Organization (WHO) notes that experts estimate that more than 50 million people experience dementia globally and that this number will likely be three times as high in 30 years’ time.
Key areas on which dementia research focuses are the possible causes of the disease and what might protect against it.
According to a 2020 report on dementia prevention, intervention, and care, the risk factors for dementia include:
- obesity
- hypertension
- alcohol misuse
- hearing loss
- traumatic brain injury
- depression
- smoking
- physical inactivity
- exposure to air pollution
- social isolation
- diabetes
- a low level of education
The report suggests that these risk factors account for up to 40% of dementia cases, meaning that, in theory, reducing these risk factors could protect a significant number of people.
Another factor that scientists think may affect dementia is cognitive stimulation levels. For example, researchers have found evidence that cognitive stimulation interventions may improve cognition for people with dementia. However, more high quality research is necessary to back up these findings.
Researchers have also been interested in understanding whether cognitive stimulation throughout life may protect against dementia. The authors of the BMJ study note that studies that have looked at this have generally been small and unable to account for potentially confounding factors.
Furthermore, researchers specifically looking at cognitive stimulation during a person’s leisure time have not found evidence of any protective effect against dementia.
Consequently, the researchers behind the present study wanted to produce a comprehensive study looking, in particular, at cognitive stimulation linked to people’s jobs.
This approach was based on the fact that people’s exposure to cognitive stimulation at work amounts to tens of thousands of hours over many years, lasting “considerably longer” than cognitive interventions or cognitively stimulating hobbies.
This principle led the team to explore this association to see whether cognitive stimulation can be protective against dementia.
More than 100,000 participants involved
The researchers drew on data from the IPD-Work consortium, which was established in 2008. This research project — the individual participant data meta-analysis in working populations — brings together 13 cohort studies looking at the relationship between work and people’s health.
The IPD-Work consortium used predefined exposure definitions and a large dataset, which meant that the researchers could draw on high quality data and convincingly identify trends within subgroups.
Of the 13 cohort studies, seven had data that researchers could use to explore the association between cognitive stimulation at work and the risk of dementia. In total, the researchers used data from 107,896 people — the largest multicohort sample to date — whom they tracked for 13.7–30.1 years, depending on the cohort.
To determine whether a participant’s job was cognitively stimulating, the researchers looked at the occupation’s levels of demand and control.
The researchers deemed jobs that were psychologically demanding and offered the worker significant control to be cognitively stimulating. In contrast, they classified “passive” jobs that had low demand and offered no control as not cognitively stimulating.
However, the team characterized cognitively demanding jobs that gave the individual no control as stressful work or job strain, which is a possible risk factor for dementia.
The researchers also looked at the relationship between cognitive stimulation and specific proteins, as well as the relationship between these proteins and the risk of dementia. These investigations involved 2,261 and 13,656 participants, respectively, and the researchers hoped that the findings would provide some clues as to a biological mechanism that could explain any associations they identified.
Significantly lower risk of dementia
“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,” the study authors concluded.
The researchers found that people who had cognitively stimulating jobs had a 23% lower risk of developing dementia compared with people whose jobs were non-stimulating.
In parallel, the incidence rate of dementia was 4.8 per 10,000 people in the group with highly mentally stimulating jobs and 7.3 per 10,000 people for those in jobs with low mental stimulation.
The researchers also found an association between cognitively stimulating jobs and specific proteins in the blood plasma that scientists believe play a role in dementia risk. Furthermore, they found evidence of a link between these proteins and a higher risk of dementia.
In a BMJ editorial covering the study, Dr. Serhiy Dekhtyar, of the Aging Research Center, Department of Neurobiology, Care Sciences and Society at the Karolinska Institutet in Stockholm, Sweden, says that the overall increased risk attributed to work that is not cognitively stimulating is less than some other risk factors, such as level of education.
Nonetheless, Dr. Dekhtyar points out that the risk reduction from doing cognitively stimulating work is still substantial — particularly in combination with a higher level of education.
For Dr. Dekhtyar, the study does, however, stand out for its high quality.
“This new work is an important reminder to all in the specialty of dementia prevention that we can only go so far with intervention studies that are short, late, small, and include only people who are heterogeneous in their risk profiles to reveal any benefit of mental enrichment on dementia risk.”
“Carefully designed, large, population-based studies with long periods of follow-up that also aim to provide biological clues can be an important addition to randomized controlled trials. Kivimäki and colleagues’ study is an outstanding example,” concludes Dr. Dekhtyar.
Too early for causal links
The head of the UK Dementia Research Institute at Imperial College London, Prof. Paul Matthews, who is a colleague of two of the study’s authors but was not involved in the research, told Medical News Today that the study is a stepping stone between animal studies looking at cognitive stimulation and dementia risk and studies investigating the effects in humans. However, there is a limit to the conclusions that researchers can draw, given that the study demonstrates an association but not causation.
He elaborated:
“[E]nvironmental stimulation improves cognition in preclinical models and may contribute to behavioral resilience in disease models. Whether similar phenomena may occur in people is of great interest, although it is by no means clear that the animal studies, which are based on extremes of environmental stimulus differences, are easy to find analogs for in human population groups.”
Prof. Matthews pointed out that the observations, although significant, were largely limited to Caucasian and Northern European groups and hence are not generalizable to a wider geographical area or people belonging to other ethnic groups.
The study, he said, also only investigates what happens in the workplace and does not explore cognitive stimulation outside of that context.
“It also cannot distinguish the potential influences of the many factors associated with more cognitively stimulating employment, including, notably, stress levels and mental health and nutrition,” he added.
Prof. Matthews acknowledged that it was still a well-conducted epidemiological study by recognized experts and that the presentation of the data was accurate and fair. However, he added:
“[W]hat they are describing is only an association. The results cannot be interpreted as suggesting [that] cognitively less stimulating jobs contribute to causing dementia or that cognitively stimulating jobs protect.”
“Because the study is observational, the authors could not control for unrecognized factors that may be important. There also are biases intrinsic to the observation, e.g., similar characteristics [such as] higher IQ may both help people secure more cognitively demanding jobs and protect from dementia,” he explained.
Prof. Matthews underlined that the study’s findings do not suggest that “a change in cognitive demands in the workplace will have an impact on dementia risk.”
He also said that it was too early to use such data to provide guidance.
Lifestyle changes for dementia
Nonetheless, according to Dr. Claire Sexton, the director of scientific programs and outreach at the Alzheimer’s Association, the study is another piece of the puzzle helping us understand the type of lifestyle that could be protective against dementia.
Dr. Sexton told MNT that the study “adds to the body of research that suggests cognitive stimulation is good for the long-term health of the brain.”
“The risk of dementia is influenced by a range of modifiable factors, from vascular health to physical activity. Cognitive stimulation has been proposed as a protective factor but can come in many means throughout the lifespan — through our education, work, or leisure activities,” she said.
Dr. Sexton echoed Dr. Matthew’s concerns about the observational nature of the study and the lack of a cause-and-effect relationship between the examined factors.
She said that further research was necessary in this area.
“While the jury is still out on the exact lifestyle “recipe” for dementia risk reduction, there are things we can do today that may decrease our risk of cognitive decline as we age. Eating a heart-healthy diet, exercising regularly, and staying cognitively engaged are just a few.”
– Dr. Claire Sexton
Future research on long-term risk
Speaking to MNT, Prof. Mika Kivimäki, the chair of social epidemiology at University College London and corresponding author of the study, said that focusing on the link between dementia risk and the proteins that he and his colleagues identified is the next step in the research.
“[W]e are keen to continue studying the associations between the [three] identified proteins and dementia risk. These associations may provide clues to search for mechanisms underlying long-term risk of dementia in humans. However, as these proteins are likely to be associated with a wide range of biological processes beyond neural influences, their effects should be comprehensively examined.”
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