One Extra Year of School in the 1970s Is Now Linked to Lower Dementia Risk Decades Later

For decades, scientists have noticed that people with more education are less likely to develop dementia — but they could never prove education was the reason, rather than genetics, wealth, or other advantages that tend to travel alongside it. Now, a quirk of 1970s British law may have finally settled the question.

A new study published in PNAS draws on the UK's 1972 Raising of School-Leaving Age Act (ROSLA), which increased the minimum age at which students in England, Scotland, and Wales could leave school — from 15 to 16. The reform applied only to students born after September 1, 1957, creating a sharp dividing line between those who had to stay an extra year and those who did not. Researchers say that cut-off date gave them something rare in medical science: the conditions for a natural experiment.

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.— Silvia Barcellos, health economist, University of Wisconsin-Madison

Barcellos and her team used data from the UK Biobank — a large-scale biomedical database — to compare the later-life health of people born just before and just after the September 1, 1957 cut-off. Those born before it could leave school at 15; those born after were required to stay until 16. Because the two groups are otherwise so similar, any difference in dementia rates between them can be attributed to that one extra year of schooling, the researchers argue.

The findings support a causal link. The researchers found a sharp decline in cumulative incidence of Alzheimer's Disease and Related Dementias (ADRD) among those born after September 1, 1957. Their estimate puts the reduction at approximately 0.88 percentage points — though they acknowledge this figure appears implausibly large given that overall ADRD prevalence in the sample was below 1 percent, and they caution that the precise magnitude cannot be reliably calculated from a sample where dementia remains a relatively rare outcome in cohorts still only in their late sixties.

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. We can credibly estimate the direction of the causal effect of education, but not its precise magnitude.— Barcellos et al., PNAS study

One of the study's most striking findings concerns genetic risk. The researchers examined participants' DNA, sorting them by whether they carried variants associated with higher ADRD risk — including the APOE4 gene, a known Alzheimer's risk factor. Among people born before the school-leaving age changed, those with high genetic risk showed significantly greater dementia incidence than their low-risk peers. But among those born after the change, the extra year of schooling was associated with a meaningful reduction in dementia incidence even within the high-risk group.

For people who know they have a higher genetic risk of dementia, this is a hopeful finding. Genes help shape disease risk, but they do not necessarily determine the outcome.— Leandro Carvalho, health economist, University of Southern California

The researchers do not claim to know exactly what it was about that additional year of schooling that produced the effect. One hypothesis is that staying in school longer raised students' qualifications, which in turn improved their income and occupational status — advantages that, compounded over half a century, may have provided meaningful protection against neurodegeneration.

The study joins a growing body of research using historical policy changes as natural experiments to test health questions that would otherwise be impossible to study ethically. Earlier this year, a separate team used a similar approach to examine the long-term health effects of wartime sugar rationing on babies in the UK during World War II, also drawing on UK Biobank data.

The researchers are careful about the limits of what they can claim. The findings stem from a specific historical moment in one country, and the cohort studied is still relatively young — meaning the full picture of dementia incidence in this group has not yet emerged. But the direction of the effect, they say, is clear, and the implications reach beyond the UK.

Our results suggest that experiences and circumstances that can be changed over the course of life may influence whether inherited susceptibility ultimately leads to disease.— Barcellos et al., PNAS study

Why it matters — If a single additional year of compulsory schooling can measurably reduce dementia risk — and partially offset genetic predisposition — it reframes education policy as a potential public health tool against one of the world's most costly and prevalent diseases.

Reported by sciencealert.com, educationengland.org.uk