One other factor, noted Grisolia, might be that some cases of Alzheimer's could be due to small strokes in the brain, a condition that wouldn't necessarily be clear to a researcher.
"One of the things that's tough about that, if you don't have a chance to examine the brains ... it's hard to tell how much Alzheimer's disease versus how much stroke damage there is in a person," he said.
In that case, patients may be benefiting by avoiding those strokes.
"Maybe that's why people with exercise are less likely to develop Alzheimer's disease," he said. "We haven't really settled the question of why exercise works."
Answer: Not really
Higher education levels -- either through schooling of self-education -- may actually help stave off declines due to Alzheimer's for longer.
"There are lots of studies that show more learning and more stimulation seems to actually protect against Alzheimer's," said Grisolia.
Patients who have higher education levels also tend to have better cognitive reserves, which helps their brain adjust to changes Alzheimer's may bring.
Karlawish said that patients with higher education levels may also have more flexible brains that can adjust to the circumstances.
However, it appears that, in some cases, these patients might decline faster once a decline begins.
"Once they get Alzheimer's, the data suggests that they tend to progress faster," said Karlawish.
At the same time, the changes might simply be more noticeable because they are more obvious in patients who often had more cognitive abilities to begin with.
"What seems to happen is that it's more noticeable because they have family members and other people who are all over it as soon as they start to get challenges," said Grisolia.
Whitehouse noted that another problem might be the work done by people with higher levels of education.
"People who have more intellectual jobs and more education tend to have more IQ in the first place," he said.
Therefore, they may be quicker to notice any changes they may experience.
While many brain games are marketed to the elderly with the promise of preventing or delaying Alzheimer's disease, it's unclear that they actually deliver on their promises.
"That's not proven for sure," said Small.
Doctors often recommend that people at risk engage in activities like crossword puzzles or other mental exercises, but the benefits aren't yet clear.
"People who exercise their minds by doing crossword puzzles, et cetera, are less likely to develop Alzheimer's down the line," said Lyketsos.
The problem, he said, is that a randomized clinical trial, where similar patients either did or did not do these puzzles and were followed to see who developed Alzheimer's, would be needed to ensure that the puzzles were helping.
"That's never been done," said Lyketsos.
Without that trial, doctors do not know if patients who do the brain exercises are helped by them, or if people who don't do the exercises and later develop Alzheimer's haven't already begun the process of decline, leading to a lack of interest in doing puzzles in the first place.