LONDON (Reuters) - Mentally demanding jobs and more education appear to protect people from the memory loss associated with Alzheimer's disease, Italian researchers said on Monday.

The findings bolster the previous research about Alzheimer's and other forms of brain impairment, said Valentina Garibotto of the San Raffaele University and Scientific Institute and the National Institute of Neuroscience in Milan, Italy.

"The theory is that education and demanding jobs create a buffer against the effects of dementia on the brain, or a cognitive reserve," Garibotto said in a statement.

"Their brains are able to compensate for the damage and allow them to maintain functioning in spite of damage."

An estimated 30 million worldwide have dementia, and Alzheimer's is the most common form.

The study published in the journal Neurology involved 242 people with Alzheimer's, 72 men and women with mild memory problems and 144 volunteers with no memory problems.

The researchers tested memory and cognitive skills and used brain scans to see how much of the brain had been affected by Alzheimer's.

They found that people with more education and more mentally challenging jobs had significantly more changes and damage in their brains from Alzheimer's -- even if they had the same level of memory impairment as people with less damage but also less education.

This was true in both people with Alzheimer's and those with mild memory problems who developed the disease during the study, suggesting the cognitive reserve is already in action before the condition sets in, the researchers said.

"The brain could be made stronger through education and occupational challenges," Garibotto said in a statement.

"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."