WASHINGTON (AP) — Seek a good education. Control blood pressure and diabetes. Get off the couch. There are some hints, but no proof yet, that these and other lifestyle changes just might help stave off dementia.

A provocative report in the British journal Lancet Thursday raised the prospect that a third of dementia cases around the world could be delayed or even prevented by avoiding key risks starting in childhood that can make the brain more vulnerable to memory loss in old age.

A recent U.S. report was much more cautious, saying there are encouraging clues that a few lifestyle changes can b...