The study looked at levels of deterioration in cognitive ability in later life and identified two distinct groups of people: one group whose cognition dropped quickly towards the end of life, and another whose cognition remained stable. Membership of the stable group was strongly influenced by childhood intelligence – more so than educational attainment or other environmental factors.
The researchers carried out the study using data from the Lothian Birth Cohort 1936, Scotland, which is one of more than 40 cohorts available to access via the DPUK Data Portal.
Lead author Dr Dorina Cadar, of the Department of Behavioural Science and Health at UCL, said: ‘There is a lot of controversy around the role played by education as a marker of cognitive reserve in relation to later-life cognition. Some studies have found a protective effect, whereas others have found no association at all. Our idea was to disentangle the role of childhood intelligence from that of education in relation to terminal decline, which represents the gradual decline in cognitive function that occurs as a function of time before death. Furthermore, we also wanted to understand whether it could be said that everyone declines in the same way as they approach the end of life.’
The Lothian Birth Cohorts are among the only long-term studies globally to feature nationwide data on intelligence from childhood through to later years, with some participants still being tested in their 90s.
Senior author Dr Graciela Muniz-Terrera, of the University of Edinburgh, said: ‘We found two distinct groups of individuals: one smaller class of about 20% whose cognitive ability dropped quite sharp towards the end of life, and a bigger group of about 80% whose cognitive ability remained stable. In addition, we investigated levels of intelligence and education – both separately and in combination – in relation to terminal decline.
‘Our findings are very interesting: when both intelligence and education were taken into consideration, intelligence showed a strong protective effect on the class membership, predicting a stable cognitive performance prior to death. However, the independent effect of education was weaker and further explained by the adjustment for childhood intelligence.’
The researchers say the role of childhood intelligence in later-life outcomes is perhaps unsurprising, given it may also be indirectly linked with environmental factors such as education level or lifestyle behaviours.
Dr Cadar added: ‘While we acknowledge limitations such as the long gaps between testing and the likelihood of older participants being “high performers”, the value of this study lies in the rarity of the data and the opportunity to analyse the impact of intelligence and education across such a broad timeframe. One possible implication is that interventions for mental development should start as early as childhood in order to be most effective across the entire lifespan, with long-term benefits for the preservation of cognitive abilities until the end of life.’
Study co-author Professor Ian Deary, of the University of Edinburgh, is Principal Investigator of the Lothian Birth Cohorts. He said: ‘We encourage researchers to become familiar with the manifold data we hold on the Lothian Birth Cohorts and to use them to test their ideas. This is one example among many in which researchers have brought good, novel research questions and worked with us to answer them.
‘In this case, what was special was the combination of childhood intelligence test scores alongside other early-life data in a cohort with repeated testing of cognitive function in older age. The findings from these analyses give some support to the quotation attributed to Fred Astaire: “Old age is like everything else… to make a success of it, you’ve got to start young.”’
Plans for follow-up research include a proposed study by Pamela Almeida Meza, a PhD student at UCL supervised by Dr Cadar, who will use the DPUK Data Portal to compare different markers of cognitive reserve across multiple cohorts in relation to neurocognitive outcomes.