Keeping the mind engaged through reading, games, and puzzles has been linked in research to delaying the onset of Alzheimer's symptoms by several years in some studies — a meaningful window, even though it doesn't prevent the underlying disease process.
The idea of cognitive reserve
Researchers describe this effect using the concept of cognitive reserve: the brain's ability to compensate for underlying damage by using alternate neural pathways. People with more cognitive reserve can tolerate more brain changes before symptoms become noticeable.
What builds reserve
Activities that require ongoing learning and novel mental effort — not passive activities — appear to matter most. Reading unfamiliar material, learning a new skill, or engaging in strategy-based games all require the brain to keep building and using new connections.
What doesn't seem to count as much
Simply repeating a familiar task, like a crossword puzzle you're already skilled at, offers less benefit than the research once suggested. Novelty and difficulty appear to matter more than the specific activity.
A realistic takeaway
Cognitive engagement delays symptom onset — it's not a guaranteed prevention strategy, and doesn't replace other protective factors like cardiovascular health and sleep. It's one piece of a broader picture, best combined with the others.