The body’s ticks and tocks
The Light Book: how natural and artificial light affect our health, mood and behaviour
by Jane Wegscheider Hyman, 1990
Ch 1 -
“Our bodies may begin measuring time before birth. In animals, and perhaps in humans, the fetus is first cued to the 24-hour cycle in the womb. Nutrients and hormones regularly cross the placenta and enter the bloodstream of the fetus. This flow from the mother, as well as her body temperature and activities, reflect her circadian rhythms, and the fetus cues its internal day according to hers.”
see also
Human Development and Fertility Cycles
The Abysmal Wheel of the Day

Midnight is placed at the bottom, to reflect the pattern of the Winter Solstice, the New Moon in their respective cycles in the Synaptic Reform Calendar.
Beginning around about midnight (individual experience guaranteed to vary)
00h00 prolactin (growth hormone) increases
02h00 body temperature at its lowest, melatonin at its highest, cortisal increases
05h00 adrenaline, heart rate and blood pressure increase
04h00 - 12h00 inflow of blood
06h00 prolactin decreases, cortisol peaks, heart rate increases
09h00 melatonin decreases, noradrenaline increases
11h00 - 12h00 sympathetic nervous system activity, and body temp. increase
15h00 blood pressure peaks
16h00 body temp. decreases, melatonin increases
22h00 blood pressure and heart rate decrease
“Researchers think that circadian rhythms are as old as life itself, enabling selected organisms to function in time to astronomical rhythms.”
10h00 - 12h00 concentration & short-term memory
13h00 - 18h00 sports, physical activity
17h00 - 21h00 practice, musical instrument
19h00 - 00h00 study & long-term memory
Zeitgeber = time giver = sunlight, the Sun
“The SCN [superchiasmatic neuclei] is called an oscillator or pacemaker because it sets the pace of the body’s various rhythms, keeping them coordinated with one another and with the Earth’s rotation.”
The SCN are connected with the pituitary and pineal glands, as well as the brain stem, which emit hormones to control the heart, adrenal glands, liver, kidneys and intestines.
“Other time cues, such as acoustic signals (e.g., an alarm clock) and a regular schedule of sleeping, waking and eating may help reinforce the Zeitgeiber.”
“The retina evolved as a protrusion of the brain. It functions, in part, as the starting point of the body’s circadian systems and appears to respond most sensitively to the green portion of the light spectrum. The retina’s light-receiving cells apparently change their structure during the day and may regulate the light information they receive.”
the eyes are most sensitive at twilight - dawn & dusk
at this time, the eyes calibrate the time of day with the season
“The retino-hypothalamic tract through which light transmits its time signals to the brain is separate from the visual pathway.”
pineal gland secretes melatonin circadianly, which in turn regulates the body’s circadian rhythm. This gland was thought to have evolved (if that’s your thing) from the reptilian parietal eye. In some species of reptile, the eye, which peeks through the top of the head, has a lens & retina.
the pineal gland is located in the centre of the brain.
29 Day cycle - skin cells rise to the surface of the skin.
Spring & Summer - heart responds better to exercise
Summer - lungs take in more oxygen
Seasonal changes in cortisol, testosterone, thyroxine and serotonin affects health, mood, sleep and sexuality.
the human immune system observes a circaseptan (7-day) cycle, however, it is thought to have been influenced by our observation of a 7-day week.
Our biological rhythms are affected by:
* artificial light
* electromagnetic fields
* stress
* chemicals (food additives, for example)
* medication
* jet lag
Ch 2 - Fertility & Childbirth
aquatic animals are tied to the rhythms of the Moon and Tides
mass breeding of aquatic species on the full moon
primate sexuality is active on the full moon
estruus and rutting have seasonal rhythms.
9 lunar cycles = 266 days
pineal gland tied to onset of puberty
ovary has melatonin receptor
menarche (onset of menstruation) at 12 1/2 years of age (9 - 18 years is normal)
in the Northern Hemisphere, menarche most often occurs in Winter.
gonadotrophins are scheduled by an hourly pulse from the hypothalamus.
light may also affect the onset of menopause (average 52 years of age)
Seasonal Peaks (in the Northern Hemisphere):
Dec Jan Feb - menarche
May - Aug/Sep + Oct - Dec - sexual activity
Mar - conception
Mar - Jun - estrogen target cells
Sep - Dec - testosterone
water breaks near New or Full Moon
labor begins & births in the dark hours
Ch 3 - Rhythms of Sleep
1 - waking to sleeping
2 - sleep
3 - deep sleep
4 - delta wave sleep
5 - REM
the nightly rhythm follows the pattern: 1-2-3-4-2-5-2-3-4-2-5-2-3-4-2-5-etc
REM
* burst of rapid eye movement
* face & limbs twitch
* heartbeat, respiration, blood pressure irregular
* penis/clitoris engorge
* uterus may increase, or contract
* intensely active Central Nervous System
* limbs remain paralysed
REM closely related to body temperature
* we spend more time in deep sleep in the Winter
* REM timing changes with the seasonal temperature
* newborns & infants 30-50% of sleep is REM
* adults 20% of sleep is REM
* from 6-8 or 9 hours a night is normal for an adult.
Ch 4 - Eating & Drinking
norepinephrine stimulates appetite
serotonin triggers satiety
chewing well allows for our feedback system to process what we’re eating, and when we’re satiated. Aids digestion.
glucose, insulin, cortisol, epidermal growth factor (EGF) in blood affect hunger
cortisol is highest just before eating
at Noon the body puts carbohydrates to use
recommended - carbohydrates in the AM, proteins in the PM
our metabolic rhythm peaks in the Winter, as do glucose and glycogen levels
06h00 - 11h00 greatest use of carbohydrates
12h00 - maximal use of carbohydrates
13h00 - peak in food metabolism
08h00 - peak in male alcohol metabolism
15h00 - peak in female alcohol metabolism
recommended - big breakfast, medium lunch, small dinner
Ch 5 - Mood & Behaviour
hibernate= to pass the winter
in Winter:
* awaken later
* eat more & heavier food
* gain weight
[bears build muscle mass while in hibernation].
Ch 6 - Skin & Bones
* ozone & the atmosphere filter out almost all Ultra-violet C (UVC), and most UVB.
* melanin in the skin filters out the rest.
* the more melanin, the darker the skin, the thicker the UV filter
UVB -> epidermis -> vitamin D -> liver, kidney, bone building
vitamin D = phosphorus & calcium balance
Every 10 Years we have a whole new skeleton.
osteoblasts + collage = bone
add calcium + phosphorus to harden the tissue
vitamin D encourages the intestines to absorb more calcium & phosphorus
UVB (and possible UVA) is linked to the development of cataracts.
Langerhans cell in the epidermis provide early warning to the immune system, and they are weakened by UV.
this can affect Vitamin A production.