Researchers point to factors that include healthier behavior such as exercising

Soaring rates of population growth and aging have long been seen as portending a global explosion of Alzheimer's, the debilitating disease that robs older people of their memory and independence.

But an unexpected, and hopeful, trend may be emerging.

In rich countries at least, recent data suggest the rate of new cases has slowed or even reversed - a tantalizing hint that quality-of-life improvements may protect against dementia.

"These findings are promising, and suggest that identifying and reducing risk factors for Alzheimer's and other dementias may be effective," said Keith Fargo, scientific director at the American Alzheimer's Association.

Overall numbers will keep growing for now - albeit at a slower rate - as more and more people live ever longer, he noted.

"We have stemmed the flow, but we haven't stopped it," added David Reynolds of Alzheimer's Research UK.

According to the World Health Organization, dementia affects some 47.5 million people worldwide - with 7.7 million new cases every year.

Alzheimer's is the most common cause, responsible for 60-70 percent of dementia cases.

The disease, which claimed actor Gene Wilder last month, typically progresses from forgetfulness and absent-mindedness to major memory loss and near total dependence as sufferers become unaware of time and place.

Toward the end, those afflicted can forget how to eat.

Alzheimer's was first identified more than 100 years ago, but there is still no effective treatment or cure, and scientists disagree on its causes.

A main culprit is thought to be the buildup of protein plaques on the brain, though one can have Alzheimer's without it.

Some recent studies have linked the condition to air pollution, fungus or even accidental transmission during a medical procedure.

New studies pointing to an Alzheimer's slowdown in rich countries, especially among men, imply that a healthy lifestyle - and plenty of brain exercise - may slow or stave off dementia.

Such trends have been observed in the United States, the Netherlands, Sweden, and Spain.

Britain had the biggest reversal - Alzheimer's incidence there dropped 20 percent in as many years.

A study in the journal Nature Communications in April reported 209,000 new cases in Britain in 2015 - far fewer than the 251,000 forecast in 1991 based on population growth and aging trends.

This meant the likelihood for British over-65s of developing dementia was "lower than it was for the previous generation", the authors concluded.

The reasons are not clear.

Some researchers point to improved cardiovascular health stemming from a growing awareness of the dangers of smoking, obesity and a lack of exercise. Better high blood pressure and cholesterol drugs may also play a role.