An active mind with intellectual pursuits in midlife may delay the onset of Alzheimer's disease symptoms, but it does not appear to stave off physical changes in the brain for most people, says a new study.

"Studies have shown that it reduces the onset of symptoms," said lead author Prashanthi Vemuri of the Mayo Clinic in Rochester, Minnesota.

But based on the new results, amyloid plaque buildups in the brain - a common trait of Alzheimer's - do not change based on activity for most people, she told Reuters Health.

The researchers studied almost 400 people age 70 and older without dementia. Of those, 53 had mild cognitive impairment, which may precede dementia.

They were divided into two groups based on years of education. Their brains were scanned to identify physical signs of Alzheimer's. Mental and physical activities were assessed with questionnaires.

The participants rated how often each month or week they had done light, moderate and vigorous exercise, heavy activities like mowing the lawn and light activities like laundry or vacuuming when they were age 50 to 65. For the same time period they estimated how often they had read books, magazines, newspapers, played games, played a musical instrument, done crafts or attended social clubs.

Neither brain volume, buildup of amyloid plaques nor brain glucose metabolism, which is a measure of brain function, were strongly tied to education level, occupation or mental and physical activities in midlife.

But people with at least 14 years of education who carried the APOE4 gene, which increases Alzheimer's risk, who kept mentally fit in midlife did have less amyloid plaque than similar people who did not stay mentally active, as reported in Neurology. One in five people carries the APOE4 gene.

It's not clear why only APOE4 carriers with 14 or more years of education would have slower plaque accumulation with midlife cognitive activity, said Anja Soldan, of Johns Hopkins University in Baltimore.

Soldan, who was not part of the new study, told Reuters Health that it's important for people to know that the researchers did not look at dementia outcomes.

Still, she said people should find activities they enjoy. If you only play chess, which is mentally stimulating, but you don't enjoy it, it may not benefit you very much.

"Find something that you enjoy, and try exposing yourself to new things that are challenging," Soldan said.

Ideally you should be doing this throughout your lifetime, rather than just starting in middle age, she added.

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