Low Blood Pressure in Elderly Increases Risk of Dementia

Jan. 14, 2004 - Diastolic blood pressure below 70 raises the risk of dementia in the elderly, says a new study of people 75 or older. For each 10-point drop in pressure, the risk of dementia increases by 20 percent. Low pressures were only linked to an increased risk of Alzheimer's type dementia, not the type that occurs as a result of blocked blood vessels in the brain.

Like the age-old question involving the chicken and the egg, the role of low blood pressure (or hypotension) as cause or consequence of dementia has long been studied by scientists. While many studies have suggested that low blood pressure is a consequence of dementia, recent findings by researchers at the Albert Einstein College of Medicine of Yeshiva University demonstrate that low blood pressure may, indeed, be a cause of dementia as well. Their research was published in the December issue of the journal, Neurology.

“In individuals with persistently low blood pressure, there was increased risk for dementia developing,” says Dr. Joe Verghese, assistant professor of neurology at Einstein. “And those participants whose blood pressure was lowered through treatment for high blood pressure also demonstrated an increased risk for dementia.”

Dr. Verghese and his colleagues at the Einstein Aging Study followed 406 elderly individuals over age 75, who all were dementia-free at baseline, at 12-to 18-month intervals. Over the 21 years that participants in the observational study were tested, 122 developed dementia. Having a low diastolic blood pressure was associated with a significantly increased risk of developing dementia, especially Alzheimer’s disease, the most common type of dementia in the elderly.

At enrollment, a detailed medical history was taken, including notations of any prescription or over-the-counter medication participants were using. Participants underwent a physical examination as well, which also included detailed blood pressure measurements and neuropsychological tests. On subsequent, annual, follow-up visits, the participants had detailed clinical and neuropsychological evaluations to determine the presence of dementia.

“The direction of the relationship between blood pressure and dementia in our older participants is opposite of that which has been found in middle-aged populations where high blood pressure, not low, increases the risk of dementia,” notes Dr. Verghese. “This may be due in part to a significant age effect.

“Aging is accompanied by significant structural and functional cardiovascular changes, leading to raised pulse pressure in the elderly,” he explains. “The rise is a consequence of arterial stiffness. Therefore, in the very elderly, higher pressures may be needed to maintain adequate blood flow in the brain – and may explain why previous studies of older populations, over age 75 have also reported low blood pressure as a risk factor for developing dementia.” 

Dr. Verghese also addresses his team’s converse finding regarding the treatment of hypertension. “In younger populations, treating high blood pressure has been associated with reduced risk of dementia,” he says. “Our findings suggest that overtreatment, or treatment that is too aggressive, may contribute to the adverse effects we found in our elderly participants. Few other studies have represented very old individuals over age 75.

“Our findings also suggest that treatment guidelines for addressing high blood pressure in the elderly might help ameliorate the risk of dementia developing.”

With low blood pressure both a cause and consequence of dementia, the question is: “Can maintaining blood pressure at optimal levels reduce the risk of dementia in elderly individuals?” It is a question that Dr. Verghese and his colleagues plan to explore.