A study carried out at the University of Southern California suggests that education levels may have a direct impact on whether a person develops dementia.
Their study backs up previous research which found that people with a limited education were at greater risk of developing the disease than those with higher education levels.
But the Californian study adds that the risks also depend on whether the individual has a genetic predisposition to learning.
Researchers looked at the cases of almost 900 pairs of twins. This included 249 pairs of twins, where both suffered from dementia. They found that almost 87% of these had received little education.
When this group was further broken down into those with Alzheimer's specifically, they found that 90% had attended school for less than six years.
However, a study of twins where just one of the pair had Alzheimer's found little differences in education levels.
Genes
This led the research team to conclude that the risks of developing the disease also depend on genes.
Margaret Gatz, lead researcher and a professor at the University of California, said: "This suggests that genetically determined abilities contribute to the protective effect of education achievement in Alzheimer's disease not the attendance of educational activities."
Over 700,000 people in the UK have dementia, a disease of the brain that causes a progressive decline in the ability to reason, to think, to remember and to learn.
The most common form of dementia is Alzheimer's, for which there is, as yet, no cure.
The results of the University of Southern California study were presented to the World Alzheimer's Congress in Washington.