Setting your circadian clock

The most highly anticipated podcast of 2021 for me was easily the Huberman Lab. Andrew Huberman, a tenured Stanford professor, uses simple language to help you understand how your nervous system operates in the context of everyday life. He also discusses tools and techniques for enhancing any aspect of your biology.

Not only is the content excellent, but Huberman is also taking the podcasting medium in an exciting new direction. Instead of focusing on a new subject every episode, this podcast will have monthly themes so that Huberman can dive deep into a topic area.

The focus in the month of January is the science of sleep, spanning the effects of light exposure, diet, exercise and other factors. What I like most about his approach is that Huberman tries to help you internalize the dynamics of your body so that you can self-experiment and figure out what works best for you, rather than offering quick hacks.

I wanted to share an insight from Episode 2 that’s had a big impact on my life.

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What drives your circadian rhythm?

Perhaps the most powerful driving force behind your cycles of wakefulness and sleep is the circadian rhythm, a 24-hour clock that exists in your brain.

This circadian clock is governed by a few things, the most important of which is light exposure. Think about why this would be the case — the circadian rhythm is an evolutionary adaptation to life on our planet, which goes through cycles of day and night every 24 hours.

When you wake up in the morning, this is because a hormone called cortisol is released from your adrenal glands. This is the “wakefulness signal”, alerting the various systems in your body that it’s time to increase your heart rate, raise your temperature, and generally get ready for the day.

It’s really important that the release of cortisol happens early in the morning, because it starts an internal timer (12-14 hours) for the release of melatonin.

Melatonin is a different hormone that is known as the “sleepiness signal”. Importantly, it is triggered by the onset of the “wakefulness signal” in the morning.

How to set your circadian clock?

In the midst of the pandemic, remote work has made it easier to wake up and go straight to work. This is an issue because we miss out on the time we would have spent outside while commuting to work.

Huberman says that you want to get direct sunlight in your eyes as close to waking as possible, and preferably before 9am, so that your internal clock is set properly.

Light coming in through a window is about 50 times less effective at triggering cortisol release than being outside.

The problem, it turns out, is that many people don’t get enough light in the morning to properly trigger the wakefulness signal and start the clock. As a result, the timing of melatonin release is delayed at night and we have trouble sleeping at a normal time.

How long and when do you have to be outside for? It ranges from 1 minute on a clear, sunny day to 10 minutes with cloud cover. The sunlight intensity also matters.

Huberman also mentions that our bodies respond particularly well to the quality of light emitted by the sun when it’s low in the sky (within a few hours of sunrise). You can still trigger the release of cortisol outside of that time frame, but it’s slightly less effective (but still much more effective than light through a window).

How well does it work? I was a little skeptical at Huberman’s claim that it only takes 2-3 days to shift your sleep schedule if you get proper light exposure in the morning. After trying it for the past week, though, I’m really shocked by how effective it is. Within just a few days of taking walks as soon as I woke up, I had no problem getting up at 7am and going to bed by 11pm.

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Huberman goes into far more detail, also touching on exercise and diet.

I should also mention that in the first episode, Huberman lays out the foundation and common terms that he will be using in later episodes. It’s little boring, but definitely worth watching.