Every morning, around 4-5am, our core body temperature is at its lowest. Our temperature rises during the day and reaches a maximum in the early evening around 6-8pm. Afterwards, our temperature decreases. This temperature fluctuation occurs in all humans and is not affected by feeding, rest-activity, light-dark cycles or sleep-wake schedules. Internal clock genes in the brain cause this automatic cycling of temperature over about a 24-hour period and it is an example of a circadian rhythm. The temperature circadian rhythm appears in babies around two months of age.
Every morning around 4-5am, our core temperature is at its lowest. Our temperature rises during the day and reaches a maximum around 6-8pm. Afterwards, our temperature decreases. This temperature fluctuation occurs in all humans and is not affected by feeding, rest-activity, light-dark cycles, or sleep-wake habits. Internal clock genes in the brain cause this automatic cycling of temperature over about a 24-hour period and it is an example of a circadian rhythm. The temperature circadian rhythm appears in babies around two months of age.
Rapid eye movement sleep (REM sleep) has a circadian rhythm component with shorter bouts in the habitual early evening and longer bouts in the habitual later evening that are maintained even with experimentally caused abnormal schedules of feeding, rest-activity, light-dark cycles, or sleep-wake habits.
Every morning, shortly after the minimum body temperature, there are high values of sleep spindle activity in non-REM sleep representing a circadian sleep rhythm component that is independent of feeding, rest-activity, light-dark, or sleep-wake habits.
‘Entrainment’ is defined as a temporal locking process in which one system’s signal frequency entrains the frequency of another system. For example, core body temperature entrains some sleep rhythms. This process is a universal phenomenon that is observed in all humans.
In adults, to get high quality healthy sleep, the night sleep episode should begin in the evening shortly after the maximum core body temperature; that is, when the core body temperature begins to decrease. When the sleep episode occurs when the brain output is in sleep mode, optimum restorative sleep occurs. Sleep quality is highest when it is in synchrony with the body’s biological sleep entrainment.
Studies of adult night shift workers show that chronic abnormal sleep schedules are often associated with adverse health consequences (Blog Posts 1–5). The night shift worker might easily fall asleep during the day after the shift ends, but because the brain is in awake mode, the night shift worker cannot maintain a long duration of sleep. When a sleep episode occurs at the time when the brain output is in awake mode, impaired sleep quality occurs (for example, jet-lag syndrome). This is the opposite of sleep being in synchrony with the body’s biological sleep entrainment. Let’s call it a train wreck.
We do know that children who have late bedtimes (Blog Post 70), who are living in cultures with habitual late bedtimes, are at risk for obesity (Blog Post 81) and other adverse outcomes (Blog Post 91). It is easier for a child to fall asleep and stay asleep (fewer night awakenings) if the sleep period occurs in synchrony with the child’s sleep entrainment (Blog Post 8 and 62). Because of the brain’s immaturity in babies and infants, watching for drowsy signs (Blog Post 9) that signal the brain entering its sleep output mode is better than watching clock time.
We do not know if children who have late bedtimes, who are living in cultures with habitually late bedtimes, have adverse consequences, but in one study, maternal sleep quality improved and maternal postnatal depression decreased when the child’s bedtime was moved earlier (Blog Post 111). The infants had longer night sleep durations of about 1.5 hours and the longest consolidated sleep bout increased by about 1 hour because of fewer signaled awakenings.
Hi Dr. Weissbluth,
My 13 month old naps in the morning from around 8:45/9 am for an hour and a half-2 hours. I put him in for another nap around 1/130, and he almost never naps. He’ll relax in his crib for a while, but I can see in the baby monitor he’s not napping. He gets fussy eventually, but usually will entertain himself for a bit.
I don’t know if he’s really ready to drop a nap and for me to push his morning nap to later? He also is waking up early in the morning. Around 5/530 am it seems. I think always before 6.
I do try to put him to sleep around 530/545 pm, if he doesn’t nap in the afternoon. I feel like maybe something just needs to be shifted with his napping and maybe he can still nap twice a day and not wake up so early? Or maybe that’s just wishful thinking…
Thanks
It is age-appropriate to think that he is transitioning to a single nap.
“I don’t know if he’s really ready to drop a nap and for me to push his morning nap to later?” Try this, but go slowly.
Thank you!
How slowly? Push it off until 930, then 10, 1030 11 etc until i reach 1 pm? Can I stretch it out over the course of a couple months or is that too gradual? He doesn’t go to daycare until September and it’s preferable if he still goes in early so that I can work while he naps (before my 3 year old comes home)…but I also want to do what’s best for my child’s sleep…
Also, about how many hours should his bed time be after his last nap?
“How slowly?” The discussion(s) in my book explains why the answer to your question is highly individualized for specific family circumstances and how well rested your child is.
“how many hours should his bed time be after his last nap?” The short answer is “based on drowsy signs” but the timing and duration of the single nap and the quality of night sleep will be influential.
I’m sorry that I can’t give you an exact answer, but does this help?
That’s okay, thank you!!
Hell Dr. Weissbluth,
Do you have anywhere in your book that discusses daylight savings time and how to handle this? Do you have any advice if not? My 10 month old sleeps well at night and has mostly good naps during the day. His night sleep is about 630pm to 630am. That will turn into 530pm and 530am if i stick to his circadian rhythm wont it? Do I just have to slowly move and get it back to the 630pm bedtime and 630am wakeup?
The well-rested child adapts quickly so you can go quickly.
From my 4th edition (deleted in the 5th)
CHANGES WITH DAYLIGHT SAVINGS TIME
When you move the clock an hour earlier or later, continue to put your child to sleep according to the new time. If her bedtime has been about 6:30 p.m. and you moved the clock ahead an hour, so her old 6:30 is now 7:30 p.m., still put her down to sleep at the new clock time of 6:30 p.m. You can ignore the time change because a lot of social cues in the family, such as active or quiet times, meals, bathing, and outdoor playtime, are adjusted along with the time change, and these social cues help regulate your child’s sleep schedule.
Hello Dr. Weissbluth,
We currently live in America and will be travelling to Australia for the holidays. I’ve been following your book since my son was 8 weeks old to much success – he started with terrible sleep, ranging from 7 to 12 hours per day, and by the time he was 12 weeks, he was sleeping from 12 to 15 hours per day. He has maintained the longer sleep hours – currently his daily average sleep is about 13.5 hours. I’m very keen for my son to continue his great sleeping as we travel. We will be in Australia for 4 weeks. What should we do to manage the jet lag and maintain his sleep schedule?
From my 4th edition (deleted in the 5th):
VACATIONS AND CROSSING TIME ZONES
Think of a vacation with your child as sort of a semi–holiday. After all, you may spend a lot of time babysitting among the palms on sun–drenched beaches. I have spent many hours building simple sand castles with one son while trying to keep an eye on a non–swimmer son jumping over small waves. This intense concentration is not very relaxing!
Try to flow with your child: be flexible, forget schedules, try to have as much fun as possible, and don’t worry much if your kids become tired. Irregularity and spontaneity are part of what make vacations fun.
When you cross two or more time zones, especially if you travel east, you might suffer the ill effects of jet lag. You are conditioned to sleep when it is dark, but activity/rest cycles and feeding habits also get messed up when you cross time zones. Children seem to be more sensitive to light, especially morning light, than adults are, so use this to help defeat jet lag. Sunlight helps regulate the internal timing mechanism. The day after you arrive (or the next day, if it is a very long trip) wake your child at the usual wake–up time. Do this both at your vacation destination, at the beginning of the trip, and when you return home after the vacation is over.
Scenario one: You leave your home very early in the morning because of holiday traffic and the extra time required because of airport security. You arrive at your destination, and it is now very late at night. By the time you claim your luggage, rent a car, drive to your hotel, and get settled, everyone is exhausted. It’s been a long day crossing many time zones! So everyone sleeps in the next morning. If your child is napping, the late morning wake–up causes the nap(s) to be later. Therefore, maybe wake up your child after a one– to two–hour nap in order to protect a reasonably early bedtime. The following morning, either wake up your child at his customary wake–up time, to reestablish his regular sleeping schedule, or repeat the process of shortening the nap to more gradually get the bedtime to its regular early time. If your child is not napping, over the next day or days control the wake–up time by waking your child either a little or a lot earlier—-and exposing him to bright sunlight, if available—-until you get to your child’s normal wake–up time.
Scenario two: The trip takes about half a day, and you arrive at your destination and get settled in by midafternoon or early evening. The day after you arrive, wake up your child at the usual time, try to give him a dose of bright sunlight, and immediately reestablish the customary sleep schedule.
Once you’re home, it’s boot camp again—-back to the basics, with all the regular routines. Maybe you will do a reset (see Chapter 4). Repeat the strategies described above. Within a few days, if you are firm, consistent, and regular, your child will learn quickly that the vacation is over. If your child was well rested prior to this vacation, expect only one rough, crazy recovery day of protest crying. I tell families that one nasty reentry night may be the price you will pay for having a lovely family vacation. Trying to gradually soothe your child back to her previous good sleep routine over several days after a vacation often fails because your child fights sleep in order to enjoy your company, which she especially enjoyed during the vacation.
A reset might be needed upon returning home and several days of a super early bedtime.
Sorry – Forgot to say that we leave America when my son is 5 months old and return when he is 6 months.
Thank you for the advice. I have the 5th edition. We leave in a couple of weeks, so I’ll be sure to implement your suggestions.
Also, the section on ‘Sleep banking’ in your edition suggests making an effort to maximize sleep during the several days before departure.