If the cardiologist's warnings don't scare you, consider this: controlling blood pressure just might be the best protection yet known against dementia.

In a flurry of new research, scientists scanned people's brains to show that hypertension fuels a kind of scarring linked to later development of Alzheimer's disease and other dementias. Those scars can start building up in middle age, decades before memory problems appear.

The evidence is strong enough that the U.S. National Institutes of Health soon will begin enrolling thousands of hypertension sufferers in a major study to see if aggressive treatment — pushing blood pressure lower than currently recommended — better protects not just their hearts but their brains.

"If you look ... for things that we can prevent that lead to cognitive decline in the elderly, hypertension is at the top of the list," Dr. Walter Koroshetz, deputy director of NIH's National Institute of Neurological Disorders and Stroke, told The Associated Press.

Age is the biggest risk factor for Alzheimer's disease and other forms of dementia that affect about one in eight people 65 or older.

Scientists have long noticed that some of the same triggers for heart disease — high blood pressure, obesity, diabetes — seem to increase the risk of dementia, too. But for years, they thought this link was with "vascular dementia" — memory problems usually blamed on small strokes, and not the scarier classic Alzheimer's disease.

140 over 90 danger signal

Now those lines are blurring as specialists realize that many if not most patients have a mix of the two dementias. Somehow, factors like hypertension — blood pressure readings of 140 over 90 or higher — that weaken arteries also seem to spur Alzheimer's-like processes.

One suspect: scarring known as white matter lesions. White matter acts as the brain's telephone network, a system of axons, or nerve fibres, enabling brain cells to communicate with each other. Even slightly elevated blood pressure can damage the tiny blood vessels that nourish white matter, interrupting those signals.

Studies show hypertension alone doesn't doom someone to later dementia. Far more people, nearly one in three U.S. adults, have hypertension.

And there are plenty of other reasons to try to reduce blood pressure. Hypertension is a leading cause of heart attacks, strokes and kidney failure.

But with dementia rising fast as the population greys, even a small effect from better blood pressure control could have a big public health impact, says Dr. William Thies of the Alzheimer's Association.

Other dementia-preventing efforts, such as targeting the sticky amyloid plaques in the brains of Alzheimer's patients, haven't panned out so far, while hypertension control has little downside, notes Dr. Lewis Kuller of the University of Pittsburgh, lead researcher of a study in which MRI scans showed women 65 and older with high blood pressure had significantly more white matter lesions in their brains eight years later.

"Until I can tell you how to get rid of amyloid in your brain, take care of the blood pressure."