Circadian management

Circadian management includes various ways to optimise one's circadian rhythm with respect to one's sleep schedule. The stability as well as the alignment of your circadian rhythm is critical to maintaining the quality of your sleep. However, depending on the timings of your sleeps and your scheduling restraints, you may or may not be able to sleep at optimal hours. To this end, it is possible to mitigate the effects of suboptimal sleep timings through shifting the circadian rhythm itself.

Circadian structure

Typical circadian timings of physiological processes

The circadian rhythm regulates a range of physiological processes that controls sleep-wake cycles. These rhythms are synchronized to local solar time when they are stabilised.

Note that, in some regions, local clock time can differ substantially from the solar time, and additional consideration is required to correctly plan circadian management measures.

Those living in red regions should subtract hours from their clock time to get the solar time, and those living in blue regions should add hours. The number of hours to add can be seen according to the colour legend below.

Typical circadian markers

Local Solar Time	Marker	Note
21:00-00:00	SWS peak
01:00-03:00	Lowest alertness	Sleep is most favoured in this time
04:00-06:00	Min. body tempeturature	This may or may not be the time with the strongest subjective feeling of coldness
06:00-09:00	REM peak
09:00-11:00	Highest alertness
11:00-17:00	Daytime nap zone	This corresponds to the circadian dip in the early afternoon.
17:00-19:00	Max. body temperature

Methods

A variety of methods can be used to optimise one's circadian rhythm. For schedules that are close to optimal ones, relatively little intervention is needed, whereas for drastically shifted schedules, strict observance of below practices wil be required.

Circadian phase response curves to light and melatonin, with 0 defined to be the nadir of the circadian core temperature rhythm.
Source: Zhu, L., & Zee, P. C. (2012). Circadian rhythm sleep disorders. Neurologic clinics, 30(4), 1167–1191. https://doi.org/10.1016/j.ncl.2012.08.011

Light exposure prior to the temperature nadir results in a delay of circadian rhythms, whereas light exposure after the temperature nadir causes phase advances. Note that there is a dead zone in the middle of the day where bright light exposure has no effect on the timing of circadian rhythms. In contrast, melatonin administered in the beginning of the night advances the circadian rhythm, while melatonin in the morning delays the circadian rhythm.

Dark period

Main article: Dark period

Dark period is a fixed daily period in which little or no melatonin-suppressing light should be allowed to enter the eyes. This is done because melatonin is essential to the stability of one's circadian rhythm. Blue, and to a lesser extent green light greatly suppresses and delays melatonin production. Left uncontrolled, this would significantly destabilise sleep and compromise its quality.

Using red- or orange-coloured laser goggles is the most common way to achieve this. For each schedule type, there is a set of recommended dark period timings, detailed in the napchart in schedule pages. It is also strongly recommended to avoid food intake and exercise in this period to align with the body's tendency to rest at night.

Those doing shifted schedules and those living near the poles may find the need to maintain dark period during daylight hours. This requires additional caution, as daylight is too strong to overcome with goggles alone. It is advised to stay indoors and use blackout curtains for this purpose.

Daylight lamps

Daylight lamp example (10000 lux). Amazon link (not sponsored)

Though necessary in appropriate amounts, it is also possible to have too much dark period. This may occur when the local day length is too short (winter), or when the dark period extends too much into the daylight hours on late core schedules.

To avoid circadian instability due to excessive darkness, daylight lamps can be used to artificially simulate daylight, lengthening photoperiod. Daylight lamps are very bright white lamps often used as a treatment for seasonal affective disorder.

Melatonin supplements

Melatonin supplements can also counteract the circadian shift caused by light. However, they may have adverse effects, such as lengthening sleep and/or increasing sleep inertia. In the long term , the health effects of supplementing melatonin is unclear. Nevertheless, it can be an effective short-term substitute for dark period to allow for a more stable circadian rhythm and ensure the quality of SWS. They should be taken shortly before sleep.

It is recommended to use as little dose as possible (<1 mg). Most supplements contain doses that are well in excess of the effective dose. Though melatonin has little toxicity, at higher doses the side effects become more pronounced.

Examples

Night shift

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