A study published in Brain Sciences has shown that mild cognitive impairment is less than half as common now as it was twenty years ago.
Two cohorts, one study
This study used data from the Interdisciplinary Longitudinal Study of Adult Development and Aging (ILSE), which began in 1992. It featured a thousand people: 500 born between 1930 and 1932 (C30), and another 502 born between 1950 and 1952 (C50).
These two cohorts were examined at four different times: T1 in 1993-1996, T2 in 1997-2000, T3 at 2005-2008, and T4 at 2014-2016. The researchers chose to compare the C30 T2 data against the C50 T4 data, as the researchers wanted to protect against the effects of repeated examinations.
Before each part of the study could begin, participants were excluded if they had diminished mental faculties, and one of the reasons was age-associated cognitive decline (AACD). 23.6 participants in the C30 cohort were excluded from T2 due to AACD, while only 9.7% of the C50 participants were excluded from T4. The C50 T4 cohort was only, on average, three years older than the C30 T2 cohort and had an average of a year more education.
Education makes a big difference
Education was found to be substantially and very significantly correlated with concentration, visual and spatial thinking, verbal fluency, executive functioning, and abstract thinking, and it also had a significant effect on word memorization.
The measured increase of intelligence over time is known as the Flynn effect, which has been confirmed in multiple studies, as another meta-analysis has shown . Other previous research has shown that education increases brain capacity in such a way that the effects of cognitive decline are less pronounced . This concept is known as cognitive reserve, and the researchers of this study concur that it is responsible for the decrease in cognitive decline.
Education did not account for all of the effects, however. Even after correcting for education, the C50 cohort scored higher on word memorization and the mosaic test than the C30 cohort did.
While this is extremely good and very welcome news, the researchers did not have a detailed explanation as to why factors other than education affected these results. Possible explanations include environmental poisons such as lead along with social effects, changes to the tests, and selection biases in the data.
This research highlights the importance of maintaining brain use and brain health. People who took care of, and built up, their brains at younger ages were able to keep them healthy and functional in older ages. Hopefully, we will soon discover ways to restore brain health, bringing back lost neurons and allowing older people to more easily learn new skills.
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 Pietschnig, J., & Voracek, M. (2015). One century of global IQ gains: A formal meta-analysis of the Flynn effect (1909–2013). Perspectives on Psychological Science, 10(3), 282-306.
 Sattler, C., Toro, P., Schönknecht, P., & Schröder, J. (2012). Cognitive activity, education and socioeconomic status as preventive factors for mild cognitive impairment and Alzheimer’s disease. Psychiatry research, 196(1), 90-95.