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.