A paper published in the Proceedings of the National Academy of Science reports on new analysis of the Survey of Health, Aging, and Retirement in Europe (SHARE), which tracks outcomes for 24,066 people aged 50-96 with a good balance of genders (56% female), and reports a strong correlation between "early affluence" and "faster cognitive drop" in "verbal fluency" (measured with an animal naming challenge). SHARE is the largest study of its kind, with more than double the subjects of similar projects.
Overall, the data showed that people whose childhoods were characterised by early affluence (measured by the subject's life circumstances at the age of ten, including main breadwinner's job, books in the house, overcrowding and housing quality) experienced cognitive decline at 1.6 times the rate of the least advantaged group in the study.
The decline was only for the "verbal fluency" measure; another measure, "delayed recall" (remembering items from a list of 10 words) did not worsen with levels of affluence.
Also, the overall levels of verbal fluency and delayed recall rose with early affluence levels.
That is, the wealthier you were as a kid, the more verbal fluency and delayed recall you had as an adult, but when you started to lose your verbal fluency, the rate of loss was faster than in those who were poorer than you as a kid.
This finding is unexpected, because it seems to contradict the leading theory of "cognitive reserve" which holds that advantaged childhoods allow people to build up "brain reserves" which are used to repair cognitive damage later in life.
Two possible explanations for the finding:
1. Survivor bias: it may be that poor people who experience loss of verbal fluency die younger, so if you experience verbal fluency loss but don't die, you're probably rich.
2. Sampling bias: it may be that poorer people were less likely to be included in the SHARE study cohort.
The study was based on six waves of the Survey of Health, Aging, and Retirement in Europe (SHARE). Researchers looked at 24,066 people at baseline who were ages 50 to 96 years; 56% of the sample was female and people suspected to have dementia at baseline were excluded. Data were collected at baseline (2004) and every 2 years after that. Childhood socioeconomic status was based on four indicators at age 10: the main breadwinner's occupational position, the number of books at home, overcrowding, and housing quality.
The researchers examined trajectories of two cognitive functions, delayed recall (assessed by a 10-word delayed recall test) and verbal fluency (assessed by an animal naming test). Over the study period, the average number of observations for each participant was 2.76 for delayed recall and 3.29 for verbal fluency.
Overall, the more advantaged the childhood environment was, the higher the levels of delayed recall and verbal fluency were in later life.
Cognitive decline was related to childhood affluence only for verbal fluency, not for delayed recall: people with a more advantaged childhood experienced more decline in verbal fluency than people with the most disadvantaged childhood socioeconomic conditions. Associations between childhood environment and level of functioning were partly mediated by socioeconomic conditions throughout the life course, but not by current levels of physical activity, depressive symptoms, or having a partner.
Advantaged socioeconomic conditions in childhood are associated with higher cognitive functioning but stronger cognitive decline in older age [ Marja J. Aartsen, Boris Cheval, Stefan Sieber, Bernadette W. Van der Linden, Rainer Gabriel, Delphine S. Courvoisier, Idris Guessous, Claudine Burton-Jeangros, David Blane, Andreas Ihle, Matthias Kliegel, and Stéphane Cullati/PNAS]
Early Affluence Tied to Faster Cognitive Drop Late in Life [Judy George/Medpagetoday]