Lowering Blood Pressure Doesn't Prevent Cognitive Impairment, Dementia
Lowering blood pressure does not appear to prevent cognitive or dementia-related disorders, a desired effect in light of the large number of elderly adults who suffer from both cognitive impairment and hypertension.
Authors of a new systematic review analyzed three studies comprising 12,091 patients with hypertension who were treated with either medication or lifestyle strategies for at least six months while undergoing testing to assess their cognitive function. All were followed for five years.
"There is no convincing evidence that lowering blood pressure prevents the development of dementia or cognitive impairment in hypertensive patients without apparent prior cerebrovascular disease," write co-authors including A. Peter Passmore, M.D., of the department of Public Health Medicine and Primary Care at Queen's University in Belfast, Ireland.
One blood-pressure medication, Nitrendipine, did appear to reduce dementia in one of the studies reviewed, but when combined with all data, this effect was not significant.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
Patients included in the study were between 60 and 89 years old with a minimum blood pressure of 160/90 and no previous cerebrovascular disease. Interventions to lower blood pressure included a variety of medications and/or lifestyle changes such as cutting salt and alcohol intake, quitting smoking and losing weight.
Vascular dementias have been linked to cardiovascular disorders, especially high blood pressure, and are often preceded by a series of small strokes. People can also suffer from a combination of vascular and Alzheimer's dementia. Hardening and narrowing of the blood vessels leading to the brain can result in gradual death of brain cells and impairments in memory, reasoning, planning and behavior.
Despite the review results, "lowering blood pressure may have beneficial effects on both atherosclerotic and blood-related mechanisms in the brain." Passmore said. "It is not clear whether it is the absolute lowering of blood pressure or the individual medications used that may affect cognition," he added.
David S. Knopman, M.D., a neurological-vascular specialist at the Mayo Clinic, says of the review, "The overall negative result of the Cochrane review can be accounted for by a number of possibilities. The studies may not have been long enough; the effects of treating hypertension probably require decades to accrue benefit. The subjects were too old and the effects of hypertension may have been sufficiently established, and damage initiated, in midlife, so that late life treatment was 'too little, too late."
He added, "Perhaps longer studies would be better, but when you deal with the elderly, there is excessive attrition from studies, which degrades the studies and makes interpretation more difficult. The problem is that the people who drop out are the sicker people, who might have been more likely to benefit from treatment."
"It is difficult to say if longer follow-up would have yielded different results," Passmore said. "The evidence from some studies suggests midlife hypertension but not late life hypertension is related to cognitive decline. It would be useful to follow younger patients for longer."
According to the National Alliance for Caregiving, the number of elderly Americans is set to double by 2050, and the number with dementia caused by Alzheimer's disease is expected to triple from current estimates of 4 million to 12 million by then.