Is dementia affected by your job?

“University graduates who perform mentally demanding jobs could be helping to ward off the symptoms of Alzheimer’s,” The Daily Telegraph reported. It said a study of over 300 people with varying levels of memory loss, including those with and without Alzheimer’s, found that those with stimulating occupations and higher educational level were less likely to suffer from memory problems associated with the condition.

This study used brain imaging to compare functional decline between people with probable Alzheimer’s, mild cognitive impairment and healthy controls. It found that, in people with probable Alzheimer’s or mild cognitive impairment that converted to Alzheimer’s, there was a significant association between higher education/occupation and lower brain glucose metabolism. In people who had comparable levels of cognitive impairment, metabolic activity was more severely reduced in those with higher education/occupation. The possible reasons for how higher education/occupation could in some way provide ‘functional reserves’ and delay the onset/severity of dementia requires further research.

Where did the story come from?

Dr Valentina Garibotto and colleagues from the Vita Salute San Raffaele University, Milan, and other institutions across Italy, Germany, Belgium and the UK, carried out the research. The work was supported by Diagnostic Molecular Imaging. The study was published in the peer-reviewed medical journal, Neurology.

What kind of scientific study was this?

The researchers say that there is a theory called ‘brain reserve hypothesis’, which is based on the idea that highly intelligent or higher educated people are better able to cope with the onset of dementia, and are able to maintain levels of brain function for longer than people who have had less education. They wanted to test this hypothesis by examining how “proxy” measures of cognitive reserve (education and occupation) relate to both the brain pathology observed on imaging scans and the clinical severity of the disease as demonstrated by neuropsychological testing.

Previous studies have shown that people with Alzheimer’s disease who have a higher educational level tend to have more severe brain pathology, but also have a similar cognitive ability as people with a lesser degree of brain damage.

This study aimed to investigate whether there is a similar “brain functional reserve” in higher educated people with amnestic mild cognitive impairment (aMCI). This is a condition that is considered to “convert” and develop into Alzheimer’s.

The design of this study was cross-sectional. The researchers used a European multicenter study (Network for Efficiency and Standardisation of Dementia Diagnosis [NEST-DD]) to recruit 242 people with probable Alzheimer’s Disease (pAD), 72 people with aMCI, and 144 healthy control subjects. The average age of the participants was 71 in the pAD group, 68 in the aMCI group, and 59 in the control group.

The participant’s educational level was assessed by number of years of formal education, including university. Their occupation was listed as their most recent position, and was graded from one (no occupation) to six (senior civil servant or management, senior academic position, or self-employed with high responsibility). All participants had extensive neuropsychological testing, including assessments of memory, information processing, and language ability. Assessments of mood and activities of daily living were also taken.

At the beginning of the study, all the participants were given brain imaging (FDG-PET), which shows metabolic activity and blood flow in regions of the brain. When they were contacted again on average 14.3 months later, they were given repeat neuropsychiatric assessments. Those who had been diagnosed with aMCI at the initial assessment were categorised according to whether they had developed Alzheimer’s or not. In this follow-up assessment, FDG-PET was not repeated, and given that these were the main data used in the correlation analyses, this study is described here as a cross-sectional study. The researchers compared the results in each of the three groups (pAD, aMCI converters and aMCI nonconverters) with the controls.

What were the results of the study?

At follow-up, 29.2% (21) of those with aMCI had converted to pAD, and 70.8% (51) had remained stable. At the beginning of the study, the pAD subjects had performed significantly worse on all neuropsychological testing than those with aMCI. Those with aMCI who subsequently converted to pAD at follow-up had performed significantly worse than those who did not convert on measures of verbal and non-verbal long-term memory and fluency.

Education/occupational score had no correlation with brain metabolic activity among the healthy controls. In those with pAD, there was the expected reduced metabolic pattern in certain regions of the brain. For a similar level of neuropsychological impairment, there was a significant relationship between both higher education and higher occupational level with lower glucose metabolism in certain temporo-parietal regions of the brain. When aMCI converters were compared to healthy controls, there was a similar significant relationship between higher education and occupation (reserve index) and lower glucose metabolism in certain brain regions. Conversely, no relationship was seen between reserve index and glucose metabolism in aMCI nonconverters.

What interpretations did the researchers draw from these results?

The researchers conclude that their study supports the brain reserve hypothesis. That is, there is significant association between a higher educational/occupational level and lower brain glucose metabolism in certain temporo-parietal regions of the brain. This suggests that those of higher education/ occupation can better cope with the same degree of brain pathology than their lesser educated counterparts.

What does the NHS Knowledge Service make of this study?

This is a complex investigational study. The research found that there was a significant association between higher education/occupation and lower brain glucose metabolism in those who had probable Alzheimer’s, or mild cognitive impairment that converted to Alzheimer’s. This was compared to no relationship in healthy controls. For those with comparable levels of cognitive impairment, metabolic activity was more severely reduced in those with higher education/occupation than those of lower.

Possible limitations to this study include:

• Those with aMCI who did and did not convert may have been at different stages in the disease process at the beginning of the study. This means that those that did not convert may have gone on to convert in several months or years’ time.
• The categorisations of educational level and occupation were broad. For example, number of years in education may not be representative of the academic ability or attainment of the individual, or the courses they were studying. As this was a multicentre study, there may also be national differences in educational systems and length of schooling. There may also have been socioeconomic factors not relating to ability or intelligence that limited what could be attained. Additionally, the participant’s last occupation may not be representative of their lifetime occupational history.
• The occupational/educational level may be confounding other factors that underlie the real association between this and brain pathology. For example, higher education/occupation being associated with improved diet and lifestyle, medical health, etc.

The possible reasons for how higher education/occupation could in some way provide ‘functional reserves’ and delay the onset/severity of dementia requires further research.