Is Low Blood Pressure a Risk for Alzheimer's in People Over 75?

Summarized by Robert W. Griffith, MD
July 29, 2004

Introduction

High blood pressure in midlife is a risk factor for developing dementia, as well as for coronary heart disease and stroke. However, things are a bit different as people get older. In people over 75, it seems that a blood pressure that's too low can also be a risk factor for Alzheimer's. A study reported in the medical journal Neurology shows that the diastolic pressure - the lower reading - is clearly linked to the risk of developing Alzheimer's in such people during the following 7 years. Here's a summary of the findings.

What was done

People aged between 75 and 85 living at home in the Bronx, New York City, were recruited. They were dementia-free at the time, and they were followed for an average of 7 years, having their blood pressure checked every 12 to 18 months.

Suspected dementia was diagnosed by a group of clinicians, neurologists, and psychologists, working together, using well-recognized criteria. Cases were sub- classified as Alzheimer's disease, vascular dementia, and dementia with Lewy bodies.

Results

There were over 400 people in the study. During the 7-year follow-up period, 30% of them developed dementia; there were 65 cases of Alzheimer's disease, 28 vascular dementias, and 29 other dementias.

The blood pressures taken at enrollment showed that those who went on to develop dementia had lower blood pressures than those who remained dementia-free during the next 7 years. The average blood pressure in those who remained dementia-free was 155/87 mm Hg, and for those who developed dementia it was 150/83 mm Hg.

This difference may not appear very large, but it was 'statistically significant', i.e. it could not have occurred by chance alone.

Further analyses showed that the difference in diastolic pressure - the lower number - was more important than the systolic or upper number. Those elderly people with a low diastolic blood pressure (70 mm Hg or below) were twice as likely to develop subsequent Alzheimer's disease, compared with those with a normal (71-98 mm Hg) diastolic pressure; the risk was even greater for people with a persistent low diastolic pressure.

There was an interesting additional finding. A mild to moderately raised systolic blood pressure (140-179 mm Hg) was linked to a reduced risk for Alzheimer's.

What this means

This study confirms the findings of a previously-reported trial; they both show that a low diastolic blood pressure is a risk factor for Alzheimer's disease in people over 75. It leaves open the question of cause and effect. Does low blood pressure mean that less blood may flow through the brain tissue, causing Alzheimer's? This doesn't seem likely, as vascular dementia was not increased in people with low diastolic pressure.

Alternatively, is a low blood pressure part of the Alzheimer's disease process by some mechanism we don't yet understand? Whatever the answer to these questions, it's probably wise for very old people to avoid drastic lowering of their diastolic blood pressure with antihypertensive drugs. And it's clear you should have your blood pressure checked regularly, whatever your age.

Remember, too, that there are things one can do to try and avoid Alzheimer's disease - see the links below.

Source

• Low blood pressure and the risk of dementia in very old individuals. J. Vergehese, RB. Lipton, CB. Hall,  et al., Neurology, 2003, vol. 61, pp. 1667--1672

Related Links
Vitamins C and E Against Alzheimer's?
Overweight Possibly Linked to Dementia in Older Women
One More Time . . .Use It or Lose It?
Moderate Alcohol Intake May Help Guard Against Dementia