People confuse cause and effect.
Until my mother’s death, just a few weeks ago, I’d spent considerable time with her in various levels of eldercare facilities. I often saw very old, but lucid, people doing crossword puzzles, Sudoku, KenKen, and other games. It’s easy to make an illogical leap and believe that the puzzles prevent dementia. The truth, however, is that such people can do puzzles because they don’t have dementia.
Alzheimer’s disease is brain damage; actual deterioration and shrinkage of brain tissue. Parkinson’s disease is neurodegenerative, first attacking motor skills but later affecting cognition. Vascular disorders, such a strokes, can deprive the brain of oxygen.
These are just several examples of irreversible causes of dementia. A lifetime of crossword puzzles won’t prevent them.
Dementia can also be the syndrome of many treatable conditions; cure the cause, and reverse the dementia. But, in these circumstances, the solution is responsible medical care, not word puzzles.