September 19, 2019
Hypertension and Dementia

Hypertension and Dementia

There’s a growing body of research
on how blood pressure affects risk for cognitive decline and dementia. Two studies published in the current issue
of JAMA add important pieces to that puzzle. Blood pressure control, especially in midlife,
could be a very strong way for this country and the world to consider, how do we
tackle dementia, which is going to be one of the major conditions that affects society. That’s Shyam Prabakharan, he wrote
an editorial about the two studies. Because it’s so simple, because it’s blood
pressure control, something we know how to do, it makes it even more of a reason to begin
to do that, even better than we do currently. Let’s look at the SPRINT MIND MRI study first. SPRINT MIND is the cognition substudy of SPRINT. And in January JAMA published
the first part of SPRINT MIND, which was a randomized trial comparing intensive
vs standard bp control and probable dementia. In that study researchers reported a
nonsignificant reduction in probable dementia in the intensive treatment group
but a significant reduction in mild cognitive impairment over a five-year
follow up in over nine thousand participants. The new MRI study was also conducted
by the SPRINT MIND research group. In the new study, the researchers report
on a subset of SPRINT participants. And in this study, the researchers looked
at structural changes in the brain. So not only are we talking about targets,
now we’re saying that there may be biomarkers in the brain that are showing protective or
beneficial changes of blood pressure lowering. The primary outcome in this study was
white matter hyperintensity on MRI imaging. White matter hyperintensities are an imaging
feature of small vessel ischemic disease. This is a form of vascular injury in the brain. If you’re looking at an MRI, white matter
hyperintensity, or white matter lesions, are best seen on a sequence called FLAIR. That’s the one in the middle. White matter hyperintensity
will show up as a bright spot. But what they mean clinically
is a little less clear. They are very commonly seen
in small levels with aging. But they are an indication of the presence of
vascular disease and especially when the amount of white matter intensity
increases to a high level, those are really indicative of
significant vascular damage. Enough to cause vascular cognitive
impairment or vascular dementia. The findings of the study were two-fold. In Sprint Mind, intensive blood
pressure lowering was able to slow down white matter hyperintensity progression, but did lead to some increase
in brain shrinkage or atrophy. The differences were small
but statistically significant. So, one has to grapple with whether, on the
one hand, reducing a biomarker associated with dementia– white matter
hyperintensity progression– is good, but is it okay for
brain volume to be reduced. And is that shrinkage, or atrophy,
going to counter the benefits of reducing white matter hyperintensity
progression, we don’t know the answer to that. The brain volume can have
multiple things going on. One thing that affects brain volume is
neurodegenerative disease for example. That tends to have a much more profound change
over time than what we saw in our group. But even things like hydration status,
for example, can change brain volume. So, we don’t actually know
what that effect is due to. I think that’s something that we want
to try and investigate a little further. Many other questions remain. White matter lesions are a risk factor
for cognitive decline and dementia, but it’s uncertain what structural and
cognitive changes might be observed with a longer follow-up. If you think about hypertension, people
are hypertensive for, you know, decades. Half their life even. And this is having effects on their brain
constantly, continually over that time period. And we were measuring a short
window in that period. And it’s this long-term effect of blood
pressure on dementia that the ARIC study, published in the same issue of JAMA, addresses. So this is the cohort called the
Atherosclerosis Risk in Communities cohort, abbreviated as the ARIC cohort,
and it was started back in 1987. So people were enrolled in this
study during middle adulthood. Having this midlife data is really what makes a
lot of the work that we do in this cohort unique because we can look at how midlife
and late life factors interact to influence late life outcomes like dementia. After enrollment, participants’ blood pressure
was measured during 5 in-person visits over 24 years. Based on these measurements, the
researchers categorized the participants into 5 blood-pressure patterns. What we did was we saw how category membership or these longitudinal blood pressure patterns
related to subsequent risk of dementia. So developing dementia in late life
after blood pressure had been measured. The findings suggest that
blood pressure even as early as mid-life may influence
longer-term cognitive outcomes. Two patterns were statistically significantly
associated with incidence of dementia: chronic hypertension and midlife
hypertension followed by late life hypotension. We did compare the two groups because we
were really interested in this question. Is the midlife hypertension, late
life hypotension actually worse than having chronic hypertension? And when we compare the two groups head to head, we didn’t see any statistically
significant differences. And that’s important. But there is some separation
between the two groups that may or may not be just a normal variation. It may be that this is all just exposure
to a longer period of hypertension from midlife onward, but there was a signal — a potential signal of increased
risk with hypotension later in life, so they could be interacting with each other
in some complex way, where it sets the stage where very low blood pressure is
particularly harmful in late life. I would encourage further research
looking at this group as, you know, picture being more pathogenic than the group
that maintains elevated blood pressure. Because I think it’s important for understanding
how to treat blood pressure in older adults, especially older adults who have a chronic
history of hypertension in midlife. And this is key. Together these studies suggest that hypertension
is a modifiable risk factor for dementia, and more intensive blood pressure control from midlife might reduce dementia
incidence in hypertensive patients.

2 thoughts on “Hypertension and Dementia

  1. Could be because of the increase in speed of life which is closely
    linked but not related to stress
    can have an unhealthy increase in blood pressure. Perhaps there exists an unhealthy and healthy increase in blood pressure?

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