Rhonda: Can you explain to people who've never heard what a circadian clock is, what it is and why it's so important?

Satchin: Yes, so all lives on this planet evolve under a rotating Earth. So that means for 12 hours, approximately 12 hours they had access to light and for another 12 hours they were in darkness. So, that environment, that changing environment put a tremendous pressure for them to come up with a timing mechanism so that they can anticipate when it's going to be evening or when it's going to be morning so that they can time their activity and sleep accordingly. So that's why almost every organism on this planet have this internal clock that help them anticipate time.

And why this is important is if you think about a diurnal organism, an animal that's active during the daytime, the animal has to anticipate when evening is going to come so that he can rush back to the cave or somewhere, some hiding place. So similarly, just before the dawn, this animal has to wake up before even light hits, and then go out and get the first grub. So that's why there is this tremendous pressure to have this biological clock or internal timing to essentially anticipate what is going to happen.

So for most people, we know when we go to bed, maybe after six to eight hours, we wake up. So our clock actually tells us, "Yes, it's going to be morning. Get up now." So similarly, almost every part of our body has clocks that help us to anticipate when the food is gonna come or when we are supposed to run, when we are supposed to take rest. So, what we are learning is almost every organ in our body has a clock and it helps this organ to be at peak performance, peak activity, at certain time of the day, and then to rest and rejuvenate at the other time of the day.

Rhonda: So, is this internal biological clock, the circadian clock, it's not something that we're just immediately born with, right? It's not something that just...

Satchin: Yes. So when we are born, we, kind of…when babies are born, they actually don't have this daily 24 hours rhythm in activity or sleep. They don't to bed for six or seven hours. So what we suspect is although they have a clock, those clocks are not wired together. And at the same time, babies also need a lot of food, because that's their growth phase. So, during the first maybe four to six months, the babies wake up in every three to four hours, cry, eat a little bit, and go back to sleep, and then wake up again, and do that.

Then after 8 to 12 weeks, they actually begin to have some kind of consolidated sleep. So they go to sleep and wake up at the right time, wake up after a few hours, but it's not tied to light-dark cycle. So they kind of drift. So that's the phase many parents may not notice because we now live in a very artificial environment, but that's the time when there is a clock but it's not tied to outside light and dark cycle. So around six months of age, that's when the whole development process and the clock is functional, it's tied to light-dark cycle, it's wired properly, so the babies go to bed, hopefully, in the evening and then sleep for nine to ten hours, wake up. So when we are born we do have clocks, but they are not connected together until about four to six months of age.

Rhonda: Oh, interesting.