Low Diastolic Pressure and Alzheimer Disease in the Very Old

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

Introduction

Hypertension in midlife is a risk factor for developing dementia, as well as coronary heart disease and stroke. However, this relationship isn't quite so clear-cut in elderly people. While treating systolic hypertension in older people reduces the incidence of dementia, hypotension can increase dementia in the very old.

This uncertainty has led to a study reported in Neurology , where a possible association between blood pressure levels in the very old and the occurrence of dementia was studied prospectively over a 7-year period. Here's a summary of the findings.

Method

The Bronx Aging Study in New York recruited 488 community-dwelling volunteers aged between 75 and 85 years. They were dementia-free at baseline, and were followed for a median of 6.7 years, having their blood pressure recorded every 12 to 18 months.

Suspected dementia was diagnosed by a consensus team of clinicians, neurologists, and neuropsychologists, according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders (3^rd revised edition). Cases were subtyped as probable/possible Alzheimer disease (AD), probable/possible/mixed vascular dementia, and probable/possible dementia with Lewy bodies.

Results

Of the original recruits, 406 (83%) were fully eligible for the study - the rest failed to attend for blood pressure recording or follow-up appointments.

During the follow-up period, 122 subjects (30%) developed dementia; there were 65 cases of Alzheimer disease, 28 vascular dementias, and 29 other dementias. At enrollment, those who developed dementia had mean lower systolic and diastolic pressures than those who remained dementia-free during the study period:

	Dementia n=122	No Dementia n=284
Systolic BP	149.8 mm Hg	155.0 mm Hg
Diastolic BP	82.8 mm Hg	86.8 mm Hg

Hazard ratios, adjusted for age, sex, and education, for every 10 mm Hg decrements of blood pressure are shown in this table:

	Any Dementia	Alzheimer Disease	Vascular Dementia
Systolic BP	1.07	1.09	1.01
Diastolic BP	1.16	1.23	1.15

It can be seen that a decrease in diastolic pressure is more relevant for this association. Indeed, people with a low diastolic pressure (70 mm Hg or below) had a significant doubling of the risk for subsequent Alzheimer disease, compared with those with a normal (71-98 mm Hg) diastolic pressure; the risk was greater for people with persistent low diastolic pressure. A low diastolic pressure did not significantly affect the development of vascular dementia.

There was an interesting additional finding - mild to moderately raised systolic blood pressure (140-179 mm Hg) was associated with a reduced risk for Alzheimer disease (hazard ratio 0.55).

Comment

This study, which confirms the findings of a previously-reported trial, shows that low diastolic blood pressure is a risk factor for Alzheimer disease in people over 75. It leaves open the question of cause and effect. Does hypotension produce reduced cerebral perfusion and thus contribute to dementia? If that were so, one might expect the relationship would be stronger with vascular dementia rather than Alzheimer disease.

Alternatively, are the low diastolic levels encountered in Alzheimer patients due to blood pressure dysregulation as part of the disease? Or, is the association due to a third, as yet unrecognized, factor?

Whatever the mechanism of the apparent effect, it seems good practice to avoid excessive lowering of diastolic pressure in very old patients - and perhaps pay less attention to slightly raised systolic pressure?

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
Two Treatable Risk Factors for Alzheimer's Disease
Alcohol and Dementias -- What To Advise?
Age-Associated Cardiovascular Changes in Health and Disease

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