High blood pressure throughout middle age may increase the risk of dementia

Controlling high blood pressure during middle age may help stave off dementia later in life.

In a long-term study, researchers monitored the blood pressure of thousands of participants five times over nearly three decades and then performed neurological tests. Having hypertension throughout one’s mid-40s to mid-60s was associated with an increased risk of dementia later in life, compared with those with normal blood pressure, researchers report August 13 in JAMA.

Among study participants who had hypertension throughout midlife, there were 3.28 cases of dementia per 100 people per year, says Keenan Walker, a neuropsychologist at Johns Hopkins University School of Medicine. Among those with normal blood pressure during middle age, there were 1.84 cases per 100 people per year.

“Hypertension is extremely common in the population and dementia is also growing in prevalence as the population ages,” says vascular neurologist Shyam Prabhakaran of the University of Chicago, who wrote a commentary accompanying the study. The study results suggest “another major reason for aggressive public health campaigns to screen [for] and treat hypertension earlier in life,” he says.

The study also indicated that either high or low blood pressure in late life increased the risk of dementia if a person first had hypertension during middle age. “How late-life blood pressure influences the brain seems to be dependent on midlife blood pressure,” Walker says.

Among people with normal blood pressure from midlife on, 1.31 per 100 people developed dementia each year, the team found. The number of new dementia cases was higher for those with hypertension from midlife on, with 2.83 per 100 people per year. But the highest risk group had hypertension first and then low blood pressure at older ages, with 4.26 new cases per 100 people per year. Previous studies have been inconsistent on whether having high blood pressure or low blood pressure late in life is a risk factor for dementia, Walker says.

The estimated number of U.S. adults who have hypertension increased recently, from around 75 million to about 116 million, largely due to updated guidelines that expanded the definition of hypertension (SN: 12/09/17, p. 13). People with this condition face an increased risk of developing cardiovascular disease. Close to 6 million in the United States have Alzheimer’s disease, the most common type of dementia.

The study began in 1987 and involved 4,761 participants from four U.S. states. Among participants, 21 percent were black and more than half were women. People had their blood pressure taken five times over 24 years, followed by neurological and psychological testing in the last decade of the study.

Hypertension was defined as having systolic pressure (how much force the blood places on artery walls when the heart beats) above 140 millimeters of mercury, with diastolic blood pressure (the force on artery walls when the heart rests) over 90. This was the standard definition of hypertension when the study began. Now, a reading of at least 130 over 80 is considered high blood pressure.

Walker and colleagues also noted whether participants had high or low blood pressure later in their lives, about 70 years and older. Low blood pressure readings were considered to be below 90 millimeters of mercury over 60.

Hypertension can damage blood vessels, making them stiffer. Past research suggests that, when the vessels in the brain are damaged, the organ doesn’t function as well, possibly because it receives less oxygen and nutrients. Then later, if blood pressure is too low, the reduced blood flow may starve the brain further.

But, Walker says, “if you can reduce the amount of vascular dysfunction” by controlling blood pressure with medication, exercise or diet, it may be possible to delay or even prevent later dementia.