1. What does the body do in the hours before the alarm rings?
In 1999, researchers published a short report in the journal *Nature*. They found that when people slept with a specific wake-up time in mind, the level of adrenocorticotropic hormone (ACTH) in their blood rose significantly about 1 hour before they woke up[1]. A hormone is a substance that travels through the blood to change how the body functions. Even though the sleeping person did not feel anything, their body had started preparing for "morning is coming." This result can be read as the body’s "prediction" of the wake-up time causing it to start preparations early. Sometimes, people wake up around the time they want to, even without an alarm. However, because the summary of this report does not specify how many people participated or exactly what times they were told to wake up, we cannot say that "this happens to everyone always."
2. How do blood pressure, temperature, and heart rate change toward morning?
Toward the morning time of the internal body clock, blood pressure, body temperature, and heart rate change to prepare for daytime activity. At night, a hormone called melatonin is released, and the body enters sleep. These body functions rise and fall in a cycle of about 1 day, or approximately 24 hours[2]. The important point here is that the body does not start moving frantically after you wake up. Instead, the preparation to rise is thought to have already progressed toward the end of sleep. The increase in ACTH mentioned earlier can be read as part of this preparation. Specific numbers for when body temperature or blood pressure rise before waking are not covered here. We can only show the direction that they "start to rise." So, where in the body does it know that "morning is coming"?
3. How does the suprachiasmatic nucleus in the brain keep track of time?
The center of the internal body clock is a small area in the hypothalamus of the brain called the suprachiasmatic nucleus. In humans, this area is less than 2 millimeters in diameter[2]. Animal studies have shown that if this area is damaged, the 24-hour rhythm of sleep and wakefulness disappears. In a 2020 study on mice at Nagoya University, it was reported that during the day, nerves in the suprachiasmatic nucleus suppressed other nerves involved in wakefulness (CRF nerves). At night, when the activity of the suprachiasmatic nucleus decreased, this suppression loosened, and wakefulness increased[3]. However, mice are nocturnal animals. It is said that further research is needed to see if the same thing happens in humans, who are active during the day. We cannot say for sure that "the brain's clock determines human morning wakefulness using the same mechanism." This clock has another feature. There are reports that the day measured by the body's clock averages 24.18 hours in humans, which is slightly longer than the Earth's day[6]. If left alone, it falls a little behind every day. Does this clock also affect the content of morning preparations?
4. Does the body clock cause the cortisol rise after waking?
In humans, a reaction where the hormone cortisol increases is seen within 30 to 60 minutes after waking. This is called the "cortisol awakening response (CAR)" and is thought to be a preparation for stress, timed to the wake-up time[4]. To investigate whether the CAR has a rhythm based on the internal body clock, independent of the effects of sleep and wake times, a laboratory study with 34 participants was published in 2022. When the influence of sleep and wake times was separated, the CAR peaked around 3:40 AM on the internal clock scale, and was barely seen at times corresponding to the afternoon[4]. A note of caution is needed here: "3:40 AM" refers to a position on the internal clock scale, not the actual time you wake up. It is simply a representation of the clock's phase using a 24-hour scale. This study showed that the hormone spike upon waking is not just the result of the action of waking up, but is also shaped by the rhythm of the body's clock. Combined with the report by Born and colleagues mentioned earlier, it is thought that the body uses clues from both the "planned wake-up time" and the "internal body clock" to prepare. So, what resets this clock, which drifts slightly every day, to match the Earth's day?
5. How does light reset the internal body clock?
It is known that when light enters the eyes, the clock genes in the suprachiasmatic nucleus are reset. This corrects the discrepancy between the internal body clock and the Earth's rotation, allowing for time adjustment[2]. An explanation from an institution belonging to the US National Institutes of Health also states that light and darkness have the biggest impact on the internal body clock. The suprachiasmatic nucleus adjusts the body clock based on information about light and darkness entering the eyes, causing melatonin to be produced more at night to induce sleepiness[5]. The flow of morning wakefulness constructed from the materials in this notebook is: use light and other clues to adjust the average 24.18-hour clock to the Earth's day-night cycle, and then use the prediction of the wake-up time to increase hormones before waking. However, this is an overall picture combining multiple studies, not a single study that showed this entire sequence. Specific numbers, such as how many minutes of light exposure are needed, are not in the materials used here, so they are not written.
6. How can you test waking before the alarm by keeping a 3-day notebook?
Try this: Set your alarm as usual, and for 3 days, write in a notebook "Did I wake up before the alarm?" and "What time did I wake up?". You cannot measure hormones at home. However, you can compare the time you wake up, or whether you wake up before the alarm rings, between "days when you decided what time to wake up tomorrow before sleeping" and "days when you slept without deciding anything." With just a few days of records, you cannot determine if there is a difference. Record for several days under the same conditions and compare. If there is no difference, consider that a result too. If you want to read the original sources, the report by Born and colleagues is published in *Nature* volume 397, pages 29-30 (1999). It is in English, but the title and abstract can be read on PubMed. The internal body clock and Nobel Prize research are covered in other notes on this site.