Moment 168: STOP Doing THIS! It's Hurting Your Sleep!: The Fitness Scientist

**Steven Bartlett** (0:03)
What is a circadian rhythm? As if you're explaining it to a 10-year-old.

**Kristen Holmes** (0:06)
Yeah, so it's basically physical, mental and behavioral changes that happen over a 24-hour cycle.

**Steven Bartlett** (0:16)
Okay. So here's my read on it, and correct me if I'm wrong. There's a clock in my head.

**Kristen Holmes** (0:25)
Yes, the suprachiasmatic nucleus.

**Steven Bartlett** (0:29)
Yeah.

**Kristen Holmes** (0:30)
Is the master clock.

**Steven Bartlett** (0:32)
Okay, which is somewhere in my body.

**Kristen Holmes** (0:34)
It's in the hypothalamus.

**Steven Bartlett** (0:35)
So it's in my brain. And this clock regulates every cell in my body.

**Kristen Holmes** (0:39)
Cell, tissue, organ.

**Steven Bartlett** (0:41)
Okay. And it releases, it controls the release of a chemical, which makes those cells, organs, every part of my body do stuff.

**Kristen Holmes** (0:52)
Yeah, so it is your hypothalamus, so the suprachiasmatic nucleus, it responds to light and it responds to darkness. Okay. So that's like the most pronounced entrainment cue for this master clock. And it then tells, it sends signals to every cell, tissue in your body as to what it needs to be doing in the presence of light, in the presence of darkness. And when we are viewing light at a phase of the natural light, dark cycle, that is, if I am awake when I should be sleeping, or I am sleeping when I should be awake, when my body anticipates that, it causes huge amounts of stress in the system. If we do this once or twice, not a big deal. But if we're doing this chronically, okay, it has massive health consequences, you know, cancer, metabolic disease, you know, cardiovascular disease, 100% of mental health issues, there will be some level of circadian disruption. Okay, so when this light information comes in and tells these clocks what to do, if I am going outside of my natural biological preferences, that is circadian disruption.
And if you think about how many folks are walking around circadian disruption, it is mind-blowing. I mean, basically, the kind of the definition that's been thrown out there is if you are awake from the hours of 10 p.m. to 4 a.m., if you're awake for two hours between 10 p.m. and 4 a.m. for two days per week, for 25 days of the year, you qualify as a kind of card-carrying shift worker and you likely have significant circadian disruption.

**Steven Bartlett** (2:54)
Which means that I have...

**Kristen Holmes** (2:56)
You are at risk for some of the, and it's not going to happen tomorrow, but if you continue on that pattern that I just described, you are putting yourself at increased risk for cancer and cardiovascular disease, metabolic dysfunction. You can have trouble having children. It impacts fertility, mental health, psychiatric disorders. There isn't a disease or disorder that circadian disruption doesn't touch.

**Steven Bartlett** (3:25)
So a way of thinking about this, so that I and everyone else can understand is there's this master clock in our hypothalamus. Look at me, hypothalamus. And this master clock regulates all of the other clocks throughout our entire body. And there's millions of them, basically. And the thing that's the master clock is using as a signal, the clock in our brain, is light and darkness. That's its most reliable. That's the signal it cares about, it listens to the most. But there's other signals as well. And if that master clock, if I'm up at 4am and I'm looking at a light at 4am, that master clock is going to start firing off chemicals to all the other clocks. And then all the clocks are going to be out of sync because then when I wake up it's light and then...

**Kristen Holmes** (4:09)
You're confusing.

**Steven Bartlett** (4:10)
I'm confusing my body and it's firing off in all kinds of different ways. So I need to form an alignment, which means basically sleeping at the right time, exposing myself to darkness at the right time, et cetera, et cetera.

**Kristen Holmes** (4:21)
Your body loves regularity.
And the problem is Moderna is not set up for that. We have access, I think all the circadian research, unfortunately, was done after the advent of electricity. So we're kind of fighting this access to constant light. And we're starting to see the, I think, deleterious effects or the negative consequences of exposure to light, really after the sun goes down. We haven't adapted to blue light after dark, right? After the sun goes down. We have not adapted to blue light.

**Steven Bartlett** (5:01)
Blue light being the light we get from screens.

**Kristen Holmes** (5:03)
Yes. There is a study that looked at the timing of light and its impact on mood and brain circuits. And they saw that if you're viewing light between the hours of, again, this is kind of this magic window of time, 10 p.m. and 4 a.m., it actually has a pro-depressive effect. So it impacts your dopamine system, reward, motivation, right? So when we wonder, you know, oh, why are all that? What is this mental health crisis? I mean, we have to look at light first. And I just don't know. And I think what's hard about the discussion and hard about this behavior is that, you know, it's really hard for people to not engage with their phones, you know, before bed. It has its own addictive properties, right? But we just have to understand that these, our relationship to light will directly influence the trajectory of our health. There's just no question about that.