There’s a lot of research showing that higher education levels are linked to a lower risk of Alzheimer’s disease, and staying in school for longer is associated with benefits to health and longevity too.But because virtually all the evidence for this comes from observational studies, it’s hard to know for sure whether education causes the positive health effects we see, or if other explanations drive the changes – like genetics, childhood circumstances, or socioeconomic factors.”We have known for a long time that people with more education are less likely to develop dementia, but it has been difficult to know whether education itself is responsible,” explains health economist Silvia Barcellos from the University of Wisconsin-Madison.Now, however, thanks to a landmark legal reform that took place in the UK in the 1970s, researchers have identified what they believe is the first evidence of its kind demonstrating a causal link between education and reduced dementia incidence.In a new study published in PNAS, Barcellos and fellow researchers investigated the long-term effects of the 1972 Raising of School-Leaving Age Act (ROSLA), which increased the minimum age at which students could drop out of school in England, Scotland, and Wales, raising it from 15 to 16 years of age.”The reform affected only students born after September 1, 1957, generating a discontinuity in the relationship between education and date of birth,” the researchers explain in their paper.Researchers believe it’s the first evidence demonstrating a causal link between education and reduced dementia incidence. (Willie B. Thomas/DigitalVision/Getty Images)That strict cut-off date created the conditions for a “natural experiment”, enabling the researchers to compare the subsequent health in later life of students who had to stay in school until 16 (the “treated” students, who are now in their late sixties) with that of their peers from directly before the change took effect, who could leave school at 15 (the “control” group).”This setting provided a unique opportunity to study the causal effects of education on Alzheimer’s Disease and Related Dementias (ADRD) incidence,” the researchers explain.”If, as hypothesized, there is a causal relationship between education and ADRD, then one would expect to observe a corresponding discontinuity in the relationship between ADRD and date of birth at September 1, 1957.”Because individuals born right before and right after this date would have had similar ADRD incidence in the absence of the policy, any observed discontinuity could be attributed to the difference in schooling engendered by the policy.”In another study published earlier this year, researchers drew upon a similar kind of historical ‘experiment’, examining the effects of strict sugar rationing on babies in the UK during World War II.In that research, scientists used data from the huge UK Biobank study to see how the WWII children’s health developed as they grew into adults, and how their health differed from contemporaneous children who didn’t experience sugar limits.Even just one extra year of schooling appeared to produce a significant effect on brain health 50 years later. (Sam Edwards/Getty Images)In their own research, Barcellos’ team also sourced their information from the UK Biobank data, and it appears to have confirmed their hypothesis about education and dementia.”Our findings indicate that education has a negative causal effect on ADRD incidence,” the researchers write.”There is a sharp decline in ADRD cumulative incidence among those born after September 1, 1957.”In the researchers’ calculations, the effects of staying in school for one year longer reduced ADRD cumulative incidence in the cohort by approximately 0.88 percentage points – an effect that the team acknowledges is implausibly large, given that the prevalence of ADRD in the sample was lower than 1 percent overall.The team suggests the anomalous result might be due to statistical factors, but while they say they can’t provide an entirely accurate estimate of the extent of the reduction in dementia cases, they say the evidence supports a causal effect.”Although our sample is large, ADRD remains a rare outcome in these relatively young cohorts, and regression discontinuity designs require very large samples to achieve precise estimates,” they write.”We can credibly estimate the direction of the causal effect of education, but not its precise magnitude.”Researchers say the findings are evidence that modifiable life experiences can alter disease susceptibility. (eclipse_images/Getty Images)In addition to measuring the reduced incidence of dementia in children who were born after 1 September 1957, the researchers also examined DNA from the study participants, sorting them into high risk or low risk for ADRD based on whether they had certain genetic variations, including the Alzheimer’s risk gene APOE4.For children born before the school dropout age changed, individuals with high genetic risk experienced significantly greater incidence of ADRD, but among those born after the change, the extra year of schooling was associated with a significant reduction in dementia incidence in the high-risk group.”For people who know they have a higher genetic risk of dementia, this is a hopeful finding,” says study co-author Leandro Carvalho, a health economist at the University of Southern California.”Genes help shape disease risk, but they do not necessarily determine the outcome.”While we can’t know for sure what it was about that extra year of education that delivered the health benefits, the researchers suggest it could have been due to socioeconomic advantages produced by additional schooling, which may have elevated their school qualifications, income, and occupational status.Compounded over a half-century, those advantages might have added up considerably, conferring protection against neurodegeneration, even in some high-risk individuals.Related: Scientists Found a Blood Signature Linked to 23% Lower Risk of DeathThere’s still a lot we don’t fully understand, and it’s worth noting that the findings here stem from unique historical circumstances.But if it happened once, maybe it can happen again.”Our results suggest that experiences and circumstances that can be changed over the course of life may influence whether inherited susceptibility ultimately translates into disease,” Carvalho says.”Understanding which interventions can produce these protective effects is an important direction for future research.”The findings are reported in PNAS.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
