#501 Sleep, Circadian Rhythm & What Actually Works (Q&A with Dr. Greg Potter)

Greg Potter (0:00)

There have been a lot of people saying, go out and see sunlight as early in the morning as possible. Straight after you wake up, the sun is up, get outside. If the sun is not up, switch on the lights to the highest intensity. And for some people, that's good advice. For some people, it's terrible advice. The reason is, not everyone wants to shift their circadian rhythm earlier. I do think that there's evidence that it's probably, in many instances, better to lose sleep at the start of the night than it is at the end of the world. We see that metabolically. If you sleep deprive people, so that they go to bed later, but they rise at the same time as previously, they tend to be better off in terms of things like lycemic control and exercise performance, interestingly, than if they go to bed at their normal time, but they're woken early, but the duration of sleep is the same in two different conditions.

Siim Land (0:46)

Greg, welcome back to the show.

Greg Potter (0:48)

Thank you, Siim. Nice to see you.

Siim Land (0:51)

Yeah, I decided to invite you back on the show to do have like a Q&A episode. We've done a lot of different podcast formats. We've done panels. We've done just solo episodes, but we haven't done like a dedicated Q&A session where my followers asked some questions from both of us. And yeah, I guess in this episode, we're mostly focusing on sleep and circadian rhythms as the core of the questions, but we also have a few other questions about other topics, which you're also very knowledgeable in. So yeah, we'll have, I think, an interesting discussion. But yeah, how are things going with you at the moment?

Greg Potter (1:33)

Yeah, all good. I warned you in advance that I'm on holiday, so I haven't had any chance to prepare for this. So this is me shooting from the hip, and therefore I apologize if some of my answers aren't very satisfactory, but I'll do my best.

Siim Land (1:46)

Well, you always give like very thought out answers, so I think it's going to be very professional shooting from the hip, if that makes sense.

Greg Potter (1:57)

Sure about that. I had a couple of beers yesterday, Siim.

Siim Land (2:00)

Okay.

But yeah, I guess we can start with the first question. Are circadian rhythms nature or nurture, and can they be changed significantly through effort?

Greg Potter (2:15)

Circadian rhythms are both, and this is often the case, but for something to truly be a circadian rhythm, by definition, it's driven by an intrinsic pacemaker which is part of your biology. It's not just a product of the behavioral cycle, such as eating at certain times each day and then repeating that day after day.

But I think what this is really getting at is chronotype. So whether someone is more of an early bird or a night owl, more nature or nurture, and certainly there is a strong genetic contribution. We see that in studies of large populations. If you take a group of people of the same age and biological sex, and you plot their mid-sleep time, the halfway point between when they fall asleep and when they finally wake up for the day.

For everyone, you'll find more or less a bell-shaped curve, where most of the people are in the middle of that distribution. But you have some people whose mid-sleep point is very early, and others for whom it's very late. This of course is confounded by various factors, like differences in the light-dark cycle, which influence the timing of the skating clock, and therefore where someone is going to fall within that distribution. What we don't really have is a similar type of analysis with very large numbers of people exposed to a standardised high-amplitude light-dark cycle, where they're getting lots of short wavelength-rich, high-intensity light during the day, and their nights are very dark, and then seeing what that distribution looks like. I think what we would find is that it's the same shape, but it's a lot narrower, because some of the people who are very owlish, just spend a lot of time indoors, and they have intrinsic circadian periods, which are longer than 24 hours. And so over time, their sleep-wake cycle drifts later, until it reached a certain point. And then they're stably entrained, but at quite a late time of day, relative to other people. So maybe the best comparator that I have to that type of experiment is when people have analyzed people before and after camping, and they found that when you take people of roughly the same age, and you look at their sleep-wake timing and melatonin rhythms before and after camping, after camping for several days, where they're exposed to minimal artificial light, the range of different sleep-wake timing and also melatonin rhythm timing between people narrows significantly. But to add one more thought, we do also know that there are mutations, variants of genes that occur in a proportion of the population that's more than 1%.