A drop in body temperature approximately two hours before natural wake-up time is a physiological marker that can be shifted.

“Approximately 2 hours prior to your final wake up time (without an alarm) is the back of the envelope way to determine your TMin.”

“Let's say I am going to travel to Europe, which is nine hours ahead typically, from California. I would want to determine my temperature minimum which for me is about 4:30 AM maybe 5:00 AM, and I would want to start getting up at about 5:30 AM and getting some bright light exposure, presumably from artificial sources because the sunlight isn't going to be out at that time.”

“Your temperature minimum is a reference point not a temperature reading.”

“In general, our temperature tends to be lowest right around 4:00 AM and starts creeping up around 6:00 AM, 8:00 AM and peaks sometime between 4:00 PM and 6:00 PM. Now that varies from person to person, but in general if we were to continuously monitor or occasionally monitor temperature that's what we would see. Now what's interesting is that even in the absence of any light cues or meal cues, we would have a shift. We would have an oscillation or a rhythm in our temperature. They would go from high to low.”

“Remember your temperature will vary according to the time of day, we did a whole episode about that related to sleep. Typically your body temperature is rising early in the day and is coming down as you approach the late evening and late night hours for sleep, in the middle of the night your temperature is very low at its absolute lowest something we call the temperature minimum.”

“But even if you don't travel, even if you don't care about things like jet lag, even if you sleep fabulously all year round, never have a poor night's sleep, knowing your temperature minimum, that time when your temperature is at its lowest point, is a valuable thing to know.”

“Instead, I know that the lowest temperature that my body will be at across the 24-hour cycle tends to be two hours before my typical wake up time.”

“The reason for writing down what time I wake up is because I want to know that average wake up time. That average wake up time informs what's called my "temperature minimum."”

“temperature minimum defines the trough, the nadir, as they say, of your temperature across the 24-hour cycle. And immediately after that, your temperature will start to rise. That temperature rise is actually what triggers the initial cortisol release that you experience and wakes you up further.”

“I know that the lowest temperature that my body will be at across the 24-hour cycle tends to be two hours before my typical wake up time.”

“If for you, your typical wake-up time is 7:00 a.m. plus or minus half an hour, and that could be 7:00 a.m. because you set an alarm clock or it could be 7:00 a.m. because you naturally wake up at 7:00 a.m., doesn't matter, if your typical wake-up time most days is 7:00 a.m., well, then your temperature minimum is 5:00 a.m.”

“ask yourself what time you normally wake up without an alarm I realize there's some variance from dayto day but you know for me it would be about let's say 6:00 a.m. so let's say for you at 7 you know just get pick your typical wakeup time if you subtract from that number so for me 4: a.m. that almost with certainty is what's called your temperature minimum your temperature minimum we could measure it you could put a thermometer in your mouth or if you come to the laboratory Unfortunately they have to do it rectally 4:00 a.m. would be my temperature minimum maybe for you if you wake up at 7 typically or around 7 it's going to be 500 a.m. okay so we're not actually measuring your temperature in this kind of Gunk and this thought experiment what we're doing is we're trying to find a time”

“The key thing is this and actually this is very valuable in general for sake of sleep so this is something I haven't talked enough about on the podcast ask yourself what time you normally wake up without an alarm I realize there's some variance from dayto day but you know for me it would be about let's say 6:00 a.m. so let's say for you at 7 you know just get pick your typical wakeup time if you subtract from that number so for me 4: a.m. that almost with certainty is what's called your temperature minimum your temperature minimum we could measure it you could put a thermometer in your mouth or if you come to the laboratory Unfortunately they have to do it rectally 4:00 a.m. would be my temperature minimum maybe for you if you wake up”

“Your temperature minimum is the point in every 24-hour cycle when your temperature is lowest. Now, how do you measure that without a thermometer? It tends to fall 90 minutes to 2 hours before your average waking time.”

“about two hours before the wakeup you see this drop in temperature and like that drop in this guy is occurring at 1:00 a.m. he's getting that drop up and then and so you what you basically were doing was dragging that thing to you know 4 a.m. you had to drag the temperature drop to 4:00 a.m.”