The authors noted that many but not all cohort studies that have examined the question have detected an association between level of education and dementia risk, and three basic hypotheses suggesting an explanation for the link have emerged.
The brain reserve hypothesis, for examples, holds that people with higher levels have greater cognitive reserves, and therefore need to experience a higher degree of pathologic changes before dementia becomes evident, they noted.
"This brain reserve could be innate or due to early life factors, and high education would be a consequence of greater reserve," they wrote. "The concept of cognitive reserve adds a functional component to this hypothesis: higher reserve could be a more efficient use of existing networks, and it could be a result of both innate factors and lifelong mental stimulation."
Alternatively, better-educated people may exercise more and eat better than poorly educated people, and therefore be better protected from dementia risk factors such as cerebrovascular infarcts (the brain-battering hypothesis).