A 6-year study has established an association between low systolic
blood pressure (SBP) and specific types of cognitive dysfunction in
elderly patients. The study of 3734 Japanese-American men in the
Honolulu-Asia Aging Study found a significant association between
low SBP late in life and prevalent dementia and Alzheimer's disease
in older patients.

Midlife hypertension is known to predict dementia, but less is known
about the interaction of blood pressure and cognitive function in
late life. The prevalence of dementia increases with age, affecting
more than 10% of those aged 65 or older and almost 50% of those aged
85 years or older. The study investigated the cross-sectional
association between low blood pressure late in life and cognitive
function, as well as the longitudinal association between low blood
pressure in late life and 6-year changes in cognitive function.

First author Gina Fujikami, MSIV, a fourth-year medical student at
the University of Hawai'i, John A. Burns School of Medicine,
Honolulu, presented the paper here at the 2008 Annual Meeting of the
American Geriatrics Association. She received the AGS Clinical
Student Research Award for the best paper in its category.

Study participants were 71 to 93 years old in 1991 to 1993. Their
cognitive ability was measured with the Cognitive Abilities
Screening Instrument. Dementia was defined as a score less than 74
(range, 0 ¡V 100). Subjects were retested after 3 years, and again
after 6 years; a decrease of 10 or more points in 3 years or 14 or
more points in 6 years was considered "cognitive decline."

SBP measurements were grouped as less than 120, 120 to 139, 140 to
159, and 160 or more. "We originally looked at under 110, and
characterized that as low blood pressure, but we lost a lot of that
end ¡X it was very low," said Ms. Fujikami, talking with Medscape
Internal Medicine. "So, you can say 115 is a little bit on the low
side, but not quite low." However, the range of blood pressures does
tend to be higher in an aging population, so 115 is low with respect
to this reference group.

Statistical analyses identified a significant association between
low SBP and prevalent dementia (odds ratio [OR], 2.70; 95%
confidence interval [CI], 1.68 ¡V 4.35; P < .0001) compared with
participants with SBP of 120 to 139. There was also a significant
association between existing Alzheimer's disease (OR, 2.20; 95% CI,
1.04 ¡V 4.66; P = .04) and low SBP. No statistical association was
found between low SBP and other types of dementia, including
vascular dementia.

There was also no significant association between diastolic blood
pressure (DBP) and dementia. "I've seen that in other studies,"
noted Ms. Fujikami, "but for our study, we didn't find any
relationship of [DBP] with dementia." During the 6-year study,
neither low SBP nor low DBP was associated with decreasing cognitive
function or incident dementia. It is possible that prevalent
dementia reflects chronic disease rather than causal effects of low
SBP.

Ms. Fujikami also raised the possibility that dementia might lead to
blood pressure changes, rather than the other way around. This could
reflect impairment in brain stem control. Other hypotheses also have
been suggested.

Session moderator George E. Taffet, MD, associate professor,
Department of Medicine, Geriatrics and Cardiovascular Sciences
Sections, Baylor College of Medicine, Houston, Texas, raised a
similar possibility in his comments to Medscape Internal
Medicine. "[The study] took advantage of a well-established, well-
characterized patient population in Hawai'i. I thought it was well-
presented and well-synthesized.... But it's too easy to say that the
horse should go in front of the cart ¡X it may be the cart in front
of the horse," he said.

"They have all the information on these patients," continued Dr.
Taffet. "They could have gone back 2 or 3 years and seen if these
patients always had low blood pressures, or if they were the ones
who were the 180 or 190 [SBP] and now developed dementia and also
were running low blood pressures."

Ms. Fujikami added: "Basically, the question now is, what's the
optimal blood pressure in very, very late life ¡X over 80 years old?
In midlife, hypertension can lead to higher rates of dementia. In
late life, should we treat them? Are we overtreating them and
causing dementia in late life? That's a question that's on
everyone's mind."