Elderly people with the highest levels of education in their youth have the best cognitive capital when it comes to facing age-related decline. The increased average time spent in education seen in recent generations could therefore at least partially explain the reduced incidence of dementia observed over recent decades in cohort studies. This is what the latest findings of an Inserm team suggest, when it compared data from two "generations" of elderly people from the PAQUID cohort.
Will education protect the next generations from age-related dementia, at least partially? While the level of education in the general population has continued to rise over recent decades, an Inserm* team has observed that this rise is linked to better cognitive performances when comparing two groups of elderly subjects with a 10-year age difference.
A number of concordant cohort studies have indicated a reduced incidence of dementia in elderly people over recent decades. In spite of this, the increases in life expectancy and world population will lead to an increase in the people with age-related dementia in the future. Forecasts suggest that 131.5 million people will be affected by the year 2050, three-quarters of whom with Alzheimer’s disease. In this context, and in order to best reinforce the prevention of dementia in the years to come, researchers are attempting to discover the factors linked to this reduced incidence.
Various factors are thought to play a role in this change: better management of diseases with vascular complications, such as diabetes, hypertension and high cholesterol, a healthier lifestyle, greater intellectual stimulation and, most notably, an increasingly high level of education.
To evaluate the impact of education level on cognitive function and decline, the researchers analyzed two groups of subjects from the PAQUID cohort, born 10 years apart. The objective of PAQUID is to study aging and its complications. When they enrolled in the cohort, the subjects were aged 65 or above and were living at home in the Gironde or Dordogne regions of France. They were followed up for 25 years and their cognitive capacities evaluated at two to three-year intervals using four tests: MMSE (global cognitive function), Isaac’s Set Test (verbal fluency), BVRT (visual working memory) and DSST (executive functioning and speed of information processing). Their autonomy was estimated with an additional test (4-IADL), looking at their ability to use the telephone, travel, take their medication correctly and manage their money. The follow-up questionnaires also concerned their profession and use of any medication for diabetes, hypertension and high cholesterol.
From this cohort, the authors created two groups of subjects aged 78 to 88, with participants born between 1903 and 1912 in the first group, and 1913 and 1922 in the second. In both groups, the authors analyzed the results from 12 years of follow-up.
A higher level of education increases cognitive reserve
They observed that the second "generation" presented a higher average education level, held more intellectually-stimulating roles and used more hypertension and high cholesterol medication than the first. In addition, it also scored higher on the four cognitive tests at enrollment. Progression which the statistical analysis shows to be mainly attributable to a higher level of education (except for working memory).
The speed of global cognitive decline was however equivalent between the two groups. Only verbal fluency and working memory declined less rapidly in the second generation, although this could not be explained by education level. There was less loss of autonomy in the second group, despite scores being equivalent upon enrollment.
"Our research confirms the beneficial impact of education on cognition. People who attained a higher level of education have a greater cognitive reserve, enabling them to better compensate for any brain lesions. Therefore, even if the speed of decline is the same in both generations, starting with a higher cognitive level makes it possible to somehow hold on to one’s cognitive capacity and autonomy for longer", concludes Leslie Grasset, first author of this paper.
*Unit 1219 Inserm/Université de Bordeaux, Bordeaux Population Health, Lifelong exposures, health and aging team, Bordeaux
L Grasset et al. Temporal Trends in the Level and Decline of Cognition and Disability in an Elderly Population: the PAQUID Study. Am J Epidemiol, online edition of June 11, 2018