The percentage of older Americans reporting serious problems with memory and thinking has declined in recent years — and higher education levels may be part of the reason, a new study finds.

Researchers found that between 2008 and 2017, the proportion of older U.S. adults reporting “serious cognitive problems” declined from just over 12% to 10%.

The reasons are unclear, but an increase in Americans’ educational attainment over time seemed to account for part of the trend.

Many studies have linked higher education levels to a lower risk of impaired thinking and dementia, said lead researcher Esme Fuller-Thomson, director of the University of Toronto’s Institute for Life Course and Aging.

One theory — the “cognitive reserve” hypothesis — is that people with more education are better able to withstand the pathological brain changes that mark the dementia process.

That is, they can function at a higher level, for longer, than their less-educated peers with the same brain changes.