The study was conducted on 242 people with Alzheimer's disease, 72 people with mild cognitive impairment, and 144 people with no memory problems.
Mild cognitive impairment is a transition stage when some memory problems are occurring beyond what is normal for a person's age but not the serious problems of Alzheimer's disease.
In the study, participants' memory and cognitive skills were tested and brain scans were used to measure the amount of brain glucose metabolism.
Brain glucose metabolism shows how much the brain has been affected by the plaques and tangles of Alzheimer's disease.
All the subjects were followed for an average of 14 months, during which 21 of the people with mild cognitive impairment developed Alzheimer's disease.
It was discovered that in people with the same level of memory impairment, individuals with more education and more mentally demanding jobs had significantly more changes and damage in their brains from Alzheimer's disease as compared to those with less education and less mentally demanding jobs.
"The theory is that education and demanding jobs create a buffer against the effects of dementia on the brain, or a cognitive reserve," said study author Valentina Garibotto, MD, of the San Raffaele University and Scientific Institute and the National Institute of Neuroscience in Milan, Italy.
She added: "Their brains are able to compensate for the damage and allow them to maintain functioning in spite of damage. There are two possible explanations. The brain could be made stronger through education and occupational challenges. Or, genetic factors that enabled people to achieve higher education and occupational achievement might determine the amount of brain reserve. It isn't possible to determine which accounts for our findings."
Garibotto said that the results were seen in both people with Alzheimer's and people with mild cognitive impairment who developed Alzheimer's during the study.
This indicated that the cognitive reserve is already in effect during the mild cognitive impairment phase before Alzheimer's begins.
People with Alzheimer's disease and people with mild cognitive impairment who developed Alzheimer's during the study had metabolic dysfunction in the areas of the brain consistent with Alzheimer's disease.
On the other hand, no brain metabolism problems were seen in healthy people and those with mild cognitive impairment who did not develop Alzheimer's disease.
The study is published in the latest issue of Neurology, the medical journal of the American Academy of Neurology.