Researchers have found more evidence of a puzzling phenomenon: Older adults who survive cancer seem to be somewhat protected against dementia.

A number of studies in recent years have found that cancer survivors have a relatively lower risk of developing Alzheimer's.

The new research adds another layer. It shows that even before their diagnosis, older adults who go on to develop cancer have an edge when it comes to memory performance.

Among the older Americans who were tracked for 16 years, those who developed cancer typically had sharper memory skills -- both before and after the diagnosis -- than those who remained cancer-free.

Researchers said it all supports the theory that some of the biological processes that contribute to cancer may actually protect against dementia.