Circadian Rhythm

What is your sleep-wake cycle dictated by?

Answer: the circadian rhythm. The circadian rhythm is a biological cycle of different processes that happen over a time span of about 24 hours.

Here are some key points in the typical 24-hour cycle:

• 6 A.M. Cortisol levels increase to wake your brain and body

• 7 A.M. Melatonin production stops

• 9 A.M. Sex hormone production peaks

• 10 A.M. Mental alertness levels peak

• 2:30 P.M. Best motor coordination

• 3:30 P.M. Fastest reaction time

• 5 P.M. Greatest cardiovascular efficiency and muscle strength

• 7 P.M. Highest blood pressure and body temperature

• 9 P.M. Melatonin production begins to prepare the body for sleep

• 10 P.M. Bowel movements suppressed as the body quiets down

• 2 A.M. Deepest sleep

• 4 A.M. Lowest body temperature

Obviously, these times are not exact and merely display the general pattern of the circadian rhythm. The exact times of your circadian rhythm will vary based on daylight, your habits, and other factors we will discuss later in this guide.

The circadian rhythm is impacted by three main factors: light, time, and melatonin.

Light. Light is probably the most significant pace setter of the circadian rhythm. Staring into a bright light for 30 minutes or so can often reset your circadian rhythm regardless of what time of day it is. More commonly, the rising of the sun and light striking your eyes triggers the transition to a new cycle.

Time. The time of day, your daily schedule, and the order in which you perform tasks can all impact your sleep-wake cycle.

Melatonin. This is the hormone that causes drowsiness and controls body temperature. Melatonin is produced in a predictable daily rhythm, increasing after dark and decreasing before dawn. Researchers believe that the melatonin production cycle helps keep the sleep-wake cycle on track.