The Science Behind Sleep Health with Minjee Kim, MD

Episode Transcript
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Erin Spain, MS (00:10):
This is Breakthroughs, a podcast from Northwestern University
Feinberg School of Medicine.
I'm Erin Spain, host of the show.
We all know how bad you can feel aftera poor night of sleep, but research
shows that the cumulative effect ofnight after night of short or disturbed
sleeping is more than irritating.

(00:32):
It has health consequences.
My guest today.
Dr. Minjee Kim studies the roleof sleep disturbance and cognitive
impairment, Alzheimer's disease andrelated dementia and aims to design
healthcare interventions for theearly detection and treatment of
sleep disturbances that could lead tolonger, healthier lives for all of us.
Dr. Kim is a Northwestern Medicineneurologist and an associate professor

(00:55):
of neurology in the division ofNeurocritical Care at Feinberg.
The research in her lab is driven by thebelief that quality sleep is a fundamental
human right, and that it's preservationis essential for healthy aging.
We welcome her to the show today to talkabout her research and innovative ways.
She's trying to bring a betternight of sleep to those who need it.
Welcome to the show, Dr. Kim.

Minjee Kim, MD (01:16):
Thank you for having me.
Such a pleasure.

Let's start with the basics.
More than half of adults donot get sufficient sleep.
What constitutes as sufficient sleepand what are some of the top reasons why
so many adults are not getting enough?

We still don't know exactly how many hours of sleep
is sufficient for an individual.
Studies of lots of people, thisepidemiologic studies have characterized
sort of how many hours people generallysleep in different life stages.
How short of a sleep is bad forvarious health outcomes, and the

(01:54):
societies have come with a guidelineto say six to eight hours of sleep
is probably what most people needin midlife and into the older age.
That being said, certain people who Icall the lucky people, don't need to
sleep that much, and they can functionjust fine, and we found some genetic

(02:15):
polymorphism associated with that.
So it's not universal thatyou need exact number.
Of hours of sleep per nightto carry out a healthy life.
But I would say generally sixto eight hours are probably a
good number for most people.

So it's not just hours that are important too,
but the quality of your sleep.

Absolutely.
Yes, so people have focused on sleepduration for many years, and a lot
of research have come about theshort sleep or longer sleep duration
and what is good and what is bad.
But, now people are recognizing thatsleep is not just about the duration.
The construct of this multidimensionalsleep health is rising, to really

(03:00):
recognize the various aspectthat constitutes sleep, right?
So good sleep, what would youthink a good sleep should be,

Oh, like you don't wake up several times in the night.
You feel rested when you wake up.

Yes.
Yes.
So sleep should function to maintainan adequate daytime alertness, right?
You should feel good when youwake up, should be refreshing
and it should be restorative.
All of that should be enough time alsoshould be consolidative that you should
not wake up too many times at night.
And the other thing that we often forgetis it should be regular from day to day.

(03:37):
You should probably go tosleep around the same time and
wake up around the same time.
So you know, there's a weekendcatch of sleep you can sleep in.
It's probably not a good sleep health.
So now we are thinking about thesevarious aspects, alertness regularity,
satisfaction, duration, and timingto define a good sleep health.

Tell me a little bit about your background as a neurologist
and what led you into sleep and nowdoing these studies on these different
age groups and different folks.

We spend about a third of our lives sleeping and
sleep isn't unique to humans.
Virtually all animals have some formof a sleep wake cycle, even though
being asleep can make them vulnerableto predators and other natural risk.
That's always intrigued me.
Like, why would such a risky behaviorbe so universal across species.

(04:29):
That sleep must serve afundamental role in our biology.
And we now know that critical processesoccur during sleep, including memory
consolidation, clearance of metabolitesthat can be toxic to brain cells.
So sleep isn't just passive rest, it'san active work that's essential for
healthy brain and bodily function.

(04:51):
I work in the neurologicalintensive care unit.
Caring for patients with severe braininjuries or those experiencing brain
dysfunction due to failure of other organslike the heart, the liver, the kidneys.
And in this setting, even the definitionof sleep becomes murky, some of my
critically ill patients are in a coma.

(05:13):
They're not awake, but they're alsonot sleeping in the traditional sense.
There are no characteristic brainwaveforms and we can't wake them up.
The injured brain appears tolose its ability to maintain a
normal sleep wake cycle or evengenerate the state of sleep at all.
So we don't yet fully understandwhether this breakdown in sleep

(05:34):
is just a byproduct of illness orwhether it's part of brain's adaptive
response, maybe even a mechanism.
Interestingly, patient in a coma who doshow sleep like activity, brain activity,
often have a better chance of recovery.
That suggests that sleep or the abilityto generate sleep may be important,

(05:55):
not just for daily functioning, butalso for healing and resilience.
But zooming out to a broader view,outside of my, clinical work.
I think we are facing increasingchallenges to maintaining
good sleep in modern society.
It's probably much harder to consistentlysleep seven to eight hours a night

(06:16):
in April, 2025 than in 1825 whenpeople use candles to get around and
didn't have the constant distractionof =emails and uh, streaming content.
So I think in modern society manyaspects of the life degrade the quality
of our sleep across the lifespanwithout us actually realizing the harm.

(06:39):
And I believe that cumulativetoll impacts our long-term health.
So that's how my research is drivennow, to find ways to improve sleep
health in everyday life, to promoteoverall wellbeing and healthy aging,
cognitive aging and aging in general.

Oh, that's fascinating.
And you mentioned light and you mentionedcandlelight versus the glow of a
smartphone, this something you studiedin several different populations.
Tell me about this work.
One study you looked at pregnantwomen, and this was published in the
American Journal of Obstetrics andGynecology, maternal Fetal Health.
Another study was published in thejournal Sleep where you looked at

(07:18):
light exposure on middle aged folks.
Light exposure, there is someimpact here on these populations.
Can you tell me about that?

I'm following really the footsteps of giants in the field
who've made major discoveries about thecircadian clock and how the circadian
clock is important and what is happeningin modern society that's really affecting
the natural circadian rhythm in our body.
So just to go back, the circadian clockit exists in all cells of our body.

(07:48):
And not just humans, but all animals.
So there is a natural light,dark cycle that's driven by the
sun and the moon to some degree.
And we've all evolved to functionoptimally in that natural setting.
With this artificial light and otherstimulus, we are getting less of that

(08:11):
natural signal that drive and synchronizeour circadian clocks in the body.
So the beliefs are that we are notgetting enough signal and there are
other random, non-natural signals thatare affecting our circadian clock.
So it's getting desynchronizedand they're not optimal to maintain
the body's functional homeostasis.

(08:34):
So that drove some of my researchinto the light exposure and
metabolic dysfunction in people.
It is really hard to disentangle thelight dark cycle, the circadian rhythms
and the sleep wake cycle becausethey're somewhat associated, right?
Then people always thought, okay, thelight before sleep is going to affect

(08:57):
your sleep and that's why it's badfor your health, and we actually also
assume that, but some of this researchwe've done seem to suggest otherwise.
So go back to the lightexposure in older adults.
This was a cross-sectional study whowere recruited a long time ago in
their twenties, and they were followedmany decades later, now in older age

(09:22):
and looked at what kind of chronicdisease they have developed and the
sleep patterns that they now had.
The caveat of that was we didn'tknow how they slept before.
And here we looked at the lightexposure during the sleep period.
And older adult who had any lightactually during their sleep period were
much more likely to have conditions likediabetes, high blood pressure, and we

(09:47):
can't infra any causal relationship there.
And it could be that people withthose conditions tend to wake up
more and they turn on the light.
But that was a one study thatstarted this journey into the
light and health research.

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Now back to the episode.

Then thanks to all the collaborators at Northwestern,
I had access to this amazing dataset of pregnant women who were
recruited between 2010 and 2013during their first pregnancy.
And here we looked at their sleeppatterns and how they were exposed to
light, just like in the older adult.

(10:34):
I was initially interested inthe light exposure during sleep
and how that's bad for them.
One major metabolic dysfunction thatoccurs during pregnancy is gestational
diabetes, so your insulin resistanceis impaired and that can lead to
many adverse outcomes lifelong.

(10:55):
So it seems natural to look atsleep pattern and light exposure
in early pregnancy and the riskof gestational diabetes, which
happens in a second trimester.
But luckily for these participants,a lot of these people had no
light exposure during sleep.
So I say, oh, that's good, butthen what happens during the day?

(11:16):
Right?
Like, you know how much of lightshould we get at what time of the day?
And we still dunno the answer to that,but if we emulate what happens in the
nature, then we should probably get a lotof light during the daytime, especially
early hours and less after sunset.
So that's how we thought aboutokay then, let's look at the hours

(11:39):
just before bedtime, because in1825 there's no light, right?
It took a lot of effort to get anylight so that, but now it takes a
lot of effort to turn off the light.
So if you get a lot of lightbefore sleep, is it going to affect
your sleep for one and two, yourrisk of gestational diabetes?

(12:00):
So then we, didn't know how manyhours is enough, so we looked
at one hour, two hour, threehour before each night bedtime.
And it actually seemed to givepretty consistent message.
So we picked three hours, which seemedreasonable based on the guideline of
defining the evening hours and women whowere exposed to most light in this period,

(12:20):
regardless of the light exposure rest ofthe day seemed to have an increased risk
of developing gestational diabetes evenafter adjusting for potential confounders.
But these women actually slept better.
So that was very strange.
And I remember just looking at thedata like, am I making mistake?
Are we doing this right?

(12:41):
So they were sleeping well.
So there was this discordancebetween the metabolic risk.
And then the traditional beliefthat the effect of light exposure
is through the effect on sleeps.
It wasn't the case.
So it seems to have an independent,adverse, effect on the metabolic
regulation, at least in this time period.

And it's important to note, you're capturing this
light exposure through kind oflike a fancy Fitbit or Apple Watch.
Is that right?
That they wear?

That's right.
So if we could choose, we would puta light sensor right here next to our
eyes, because that's how our brainsees the light, and that's how our
circadian clocks perceive the light.
But we still don't have a devicethat's convenient enough to do that.
So we capture light at the wristlevel as our participants to wear this

(13:32):
let's say fancy version of Fitbit foranywhere between seven to 14, sometimes
longer days, and capture the lightexposure throughout those periods.

So that's interesting.
It kind of opens up this whole newworld of not only do you have to worry
about your duration and quality ofsleep, but then your light exposure
during the day and before bed.
So lots to explore there.
You know, what practical stepscan people take to reduce their
risk of light exposure at night?

I would say just be mindful first of all of what
lights are around you, and I'mactually gonna share this constant
kind of battle with my husband.
I have two young children,there are three and seven.
There are more research comingout demonstrating how sensitive
children are to this evening light.
So to adult we generally say dim lightless than 5 to 10 watts is probably okay.

(14:27):
Recent research suggestedchildren even at a very dim light.
Their melatonin goes now it's not good.
So then it's very hard to turn upall the light because night light
we have stairs and the safety.
So we try to dim most light andthen turn up screen for one.
I actually have glassesthat block blue light.

(14:48):
The evidence is, you know's, comingup, it's we'll see it's jury's
still out there, but at least that'ssomething that I am doing that
I think people can easily adopt.
It's not as easy to reduce the light levelat home, but you can turn off the devices.
And, you know, turn up the bluelight mode and then use warmer

(15:09):
light nightlight if you have to.
Just dim everything and be mindful of it.
And, you know, those glasses areinexpensive and it probably wouldn't hurt.
I don't know if there are benefitsyet, but the jury's out there hopefully
will have more evidence on that.

So there's been two studies recently you've done
with either pregnant or postpartumwomen looking at metabolic health.
Tell me about that populationand why it is that you were
so interested in studying them
. Minjee Kim, MD: Generally in the field, a lot of studies have been
done looking at the link between sleepand cognitive function and aging.
What people are realizing now is thatit might be chicken and egg situation.

(15:48):
Poor sleep likely leads to poorbrain function, but the poor brain
also cannot generate good sleep.
So then are you actually looking atthe byproduct of a brain changes and
calling it as a risk factor becausethese changes happen at the same time?
So then can we do something aboutit if it's actually in your brain
unable to generate good sleep?

(16:08):
So the field is moving to anearlier life stage, midlife.
And for women specifically, thechallenges are unique to them,
including pregnancy and menopause.
Right?
We know that short sleep duration islinked to many adverse health outcomes.
Cardiovascular disease calleddecline, even mortality.
And this relationship seemsto vary by age and sex.

(16:30):
Men and women separatelyand also cross life stages.
So that's how I was interestedin this cohort study that
followed the pregnant women.
Who were pregnant between 2010 and 2013,it's ongoing now, ten year follow up.
Now they're entering middle age and theyhave been characterized for all kinds

(16:51):
of biological and psychosocial changes.
So then can we look at some ofthe changes that happen in their
early or just before the midlife.
And there must be somethingthat can be intervenable.
The previous research have focused onpregnancy and menopause, but there have
been gap between those two life events.

(17:11):
There are parenting years, it'shard to maintain good sleep.
There's so many challenges, and Imay even say that sometimes harder
than the pregnancy itself and thepeople also have multiple pregnancies.
The middle of the night feedings and bad dreams, and
getting up to tend to children,that can be very disruptive.

Very disruptive, right.
So that the research that have beendone in the immediate postpartum period,
six month, one year, even up to twoyears and how women sleep, even feeding
schedule can affect overall wellbeing.
But then the study really drops out.
We don't know what happens after thatwhen most children would sleep through

(17:52):
the night, but still there are challenges.
So that's what we were interested in,like what happens in these early parenting
years, and if people either developa new inadequate sleep or continue to
have inadequate sleep then would thataffect their long-term metabolic risk?
So we leveraged the data set of pregnantwomen who were enrolled during their

(18:14):
first pregnancy and followed two toseven years after the index delivery.
And about 4,000 women reported bothsleep duration during the pregnancy,
and again, a follow up that was about3.1 years of interval The median sleep
duration decreased from eight hours toseven hours, so people sleeping less.
About quarter of them had less thanseven hours of sleep during pregnancy,

(18:39):
which then rose to 35% at follow up.
But there was significant shift.
Some people now have new short sleep andsome people have resolved short sleep.
So there are changes, and what wefound was that about 13% of the
participants developed a metabolicsyndrome at follow-up, which is a
constellation of conditions likehigh blood pressure, dyslipidemia,

(19:01):
obesity, and insulin resistance.
And this is thought to be a significantrisk factor for cardiovascular
morbidity and mortality later.
And people who had the persistent shortsleep, meaning slept less than seven
hours, both during pregnancy and at followup, were at significantly higher risk
of developing this metabolic syndrome.
Just over three, little overthree years of follow up.

(19:23):
And when we define the short sleep asless than six hours, so it's more severe
short sleep, the risk seemed even greater.
Now, having short sleep at eithertime point or both time points were
all associated with the greater risk.
So there might be a dosedependent relationship between
short sleep and metabolic risk.
I think this is important to knowbecause metabolic syndrome is

(19:46):
considered a modifiable risk factor.
So this might be the time to intervenebefore these women go on to develop
a full-blown cardiovascular disease.
Also interesting is that otherlongitudinal studies have
shown that sleep duration isrelatively static across midlife.
So people who sleep little,continue to sleep a little for

(20:08):
20 years from age forties and on.
But we saw a lot ofshift in sleep duration.
So this is a time that peopleare vulnerable to establishing
suboptimal sleep habits and maybewe should do something about it.
And the other thing is that the burdenof inadequate sleep duration was not

(20:29):
uniform across racial and ethnic groups.
The non-Hispanic Black mothers weremuch more likely, almost twice as likely
to develop unusual short sleep andmore than twice as likely to continue
to have short sleep at follow up.
We don't know what's driving this, thereare probably multiple factors including
structrual racism and other thingsthat we can address in different ways.

(20:52):
So this is going likely toexpand and widen the health
disparity over the lifespan.
So think the next step for the fieldis really to think about developing an
intervention in this life stage that'sculturally appropriate that can modify
the long term cardiovascular and alsothat leads to neurologic risk over time.

What do you that could look like?

Even something simple like awareness and counseling of sleep habits.
Turn off the light and try tomaintain consistent time for bed.
So if you think about I need to go tobed at nine o'clock to maintain seven
hours of sleep, then start turningoff the light at seven and then
winding down at eight so that you aremore likely to fall asleep at nine.

(21:40):
So just be mindful of that, not likeyou constantly doing something up until
nine o'clock and I gotta go to bed.
It's much harder to turn that off.

So you're currently working with other Northwestern
investigators on the MidCog study.
Explain this study to me and howit contributes to your research
on sleep and cognitive function.

Yes, so my mentor and collaborator, Dr. Michael Wolf, is a
phenomenal researcher and he has carriedout a longitudinal cohort study of
older adults over almost two decades.
We've learned a lot about what happensin older age, but now we are realizing
that a lot of risk factors actuallystart developing in earlier life stage

(22:20):
in midlife, as we talked about earlier.
So this is his new cohort study, thatis looking at potentially modifiable
risk factors of cognitive aging inthis lifespan.When I started talking t
o him back in 2021 we clicked becauseI've always been interested in sleep,
but not in this general population,and he's carried out successfully

(22:45):
this cohort studies for many years,but he has not investigated sleep.
So I say, let's collaborate on this.
Let's add a sleep aspect to this.
I think this is a major gap.
So this cohort study recruitsabout 1200 people from the greater
Chicagoland area from primary care.

(23:06):
And we are characterizing potentiallymodifiable risk factors, including
physical activity, diet, andchronic conditions, vital signs
plus sleep and rest patterns.
We're asking them to report theirsleep quality using multiple
validated questionnaires.
We're also asking them to wear thisfancy version of Fitbit to characterize

(23:30):
their rest activity patterns.
What we are trying to achievewith this cohort is to better
understand what happens in midlife.
Like how do people sleep?
There are major gaps in that knowledgeand what aspect of sleep is particularly
bad for your health, not just now,but also at a lot later life stage,

(23:53):
that we can do something about it.

And you're leveraging AI and the electronic health records
as well, to develop tools to maybedetect people who have sleep issues but
aren't being treated for the problem.
First, tell me about this problem of sleepissues being overlooked in primary care
and how you plan to tackle this problemwith AI and electronic health records.

Yes.
Actually, this is completely newareas that I'm delving into.
Many years that I've used and leveragedthis core studies, I was always a little
bit flustered by the fact that thereare all these observational studies
suggesting that poor sleep is bad for you.
There have been relative palsy ofintervention studies showing that

(24:35):
what we can do about it, and I thinkone of the major roadblocks there is
that it's hard to find these peoplewith poor sleep, no matter how you
define it, because it's not on yourchart and people don't advertise it.
So even though one third of peoplesleep not enough, you have to put in
significant effort to identify thosepeople and screen them, make sure

(24:56):
that they're eligible for studies.
It's very labor intensive.
And once you find an interventionthat works in this group of people,
how can you implement and all thesepeople, you again have to find them
as I was sort of struggling with thisgap between the knowledge they we're
accumulating and what we can do about it.

(25:16):
Now there is this major advancesin artificial intelligence and also
widespread use of electronic healthrecords, and this seems to be really an
optimal combination that can change andtackle these roadblocks that we've had.
What we are trying to do isutilizing this functionality.
So let's say this MidCog study isrecruited through primary care, and

(25:40):
because of that we actually have access tothe participant electronic health records.
So.
What we are trying to do is, okay, sowe identify these people with sleep
problems of the different types.
Can we now predict who's gonna havethese problems without asking them
to wear all this fancy watch andanswer questions and questionnaires

(26:02):
using artificial intelligence?
Then if we do that, then can we nudge theclinicians when the patients come to see
them for annual visit or anything else?
You are at risk of sleep problem,that's bad for you and it might
trigger a simple question.
And if it seems to be the case, thenokay, then there's something that we

(26:24):
can send you to, we can refer you or wecan provide some sleep hygiene things
that they can do something about.
We don't know whether that'sgonna work, but at least that's,
the idea of the next steps.

Okay, so this is really new.
As you mentioned, you'redoing a pilot of this?
What Can you tell me about that?

So the pilot study that we just completed was trying
to find sleep apnea in older adultsin primary care and send them to
diagnostic studies than treatment.
It was a minimal effort for the cliniciansor the patient we send a screener, that's
a four item questionnaire to patient whoare 65 and above who come for wellness

(27:03):
visit, and if they answer those questionsin a way that seem to be at risk of
sleep apnea, then the clinicians areautomatically nudged to ask them about
sleep habits and order diagnostic study.
Then what we wanted to know in thispilot study was, is this gonna work?
Like, do people find this burdensomeor do people actually follow

(27:26):
through with the recommendation?
We were actually surprised that theseolder adults, over 40% of them actually
did complete the screener and, asignificant number of them followed
through with the recommendations and werediagnosed and started treatment for that.
So minimal effort was not costly butmade some differences in people.
So that was the pilot study thatwe're going to also utilize for

(27:49):
the next step in different settingsand also in middle age adult.

You've been really busy, you've been putting out a lot of studies.
You're working on these pilotprojects, you're working with all
these investigators, you know, whatdo you hope happens with your lab and
your work in the next 5 to 10 years?

I have a lot of ideas, but what I would like to focus
on s this pilot study of utilizingAI and electronic health record
functionalities to intervene or detecta bad sleep patterns or suboptimal
sleep patterns and intervene on yeah.
I think that's where I would reallylike to focus my efforts on, because
that's scalable, that can be modifiedin different settings, and that's

(28:28):
my dream and the goal, like, youknow, can we all sleep better?
That's a fundamental humanright that we don't know about.
And then, you know, but I think weshould all sleep like it was 1825.

I love it.
Well sleep like it's 1825.
That's great.
Thank you so much for allthis insight and sharing the
incredible work that you're doing.
I really appreciate it.

Thank you.

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(29:13):
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