THE BRAIN
The first third of the night is spent mostly
in N3, or deep sleep, which, along with
REM, is important for storing memories and
pruning useless thoughts
—
so “sleeping
on a problem” does help you gain clarity.
In fact, your brain is probably the biggest
beneficiary of snooze time, says Mark Wu,
M.D., Ph.D., associate professor of neurology
at Johns Hopkins School of Medicine. In
recent years, scientists have also discovered
a new brain pathway, labeled the “glymphatic
system,” that removes excess proteins,
fluids and other waste from the brain and
spinal cord
—
a possible reason Alzheimer’s
is more common in those who don’t get
adequate sleep.YOUR EYES
We spend a quarter of the night in REM
sleep, during which all muscles relax except
the heart, lungs and eyes. Why our peepers
stay active isn’t known, but one theory is
that we’ve adapted this way because if danger
rockets you awake, ready-to-go vision could
save your life.YOUR MUSCLES
In N3, growth hormones are secreted, and
they play a role in repairing and building
muscles
—
this is a main reason that athletes
consider shut-eye an important part of their
training, Dr. Wu says. While muscles function
normally during much of the night, the
fact that they are immobilized during REM
means you won’t act out aggressive dreams
and punch your partner!SKIN
A study of 60 women (all of whom were
white) by Cleveland’s Case Medical Center
found that getting too little shut-eye made
them look older, and it also weakens the
skin’s external barrier, which keeps water inand bacteria out. Skimping may also alter
the production of collagen and accelerate
its breakdown, says Noelani González, M.D.,
director of cosmetic dermatology at Mount
Sinai West in New York City.THE HEART
Your heart beats all night, of course, but by
early morning coronary arteries are at their
stiffest. Unfortunately, this is when blood
pressure and heart rate increase
—
the mis-
match is one reason heart attacks are more
common in the a.m.HORMONES
The hunger hormone ghrelin, which drops
naturally at night, and the satiating hormone
leptin, which stays high, can’t regulate your
appetite when you’re not rested, which may
be why sleeplessness leads to overeating
and weight gain. Having proper levels of
thyroid stimulating hormone also requires
good slumber.DIGESTION
While you sleep, saliva production drops
from 0.5 milliliters per minute to nearly zero,
and you swallow one-fifth as often
—
that may
explain dry mouth and morning breath. Too
little moisture is a problem if you’re prone
to reflux, as less saliva gives your pipes less
protection when acid backs up. Digestion also
slows, along with the muscle contractions in
your intestines that push food through.THE IMMUNE SYSTEM
During slow-wave sleep, your body ramps up
production of a substance called cytokine that
boosts immunity. “You’re more likely to get
sick if you haven’t slept well,” Dr. Shamim-
Uzzaman says. Vaccines are also aided by
slumber: In one study, people who were kept
up the night after a shot had half the immune
response of those who slept.while you were
SLEEPING
Here’s what goes on in your body when you’re
in lights-out mode68 GH OCTOBER 2019
Health s ecial re ort THE FOUR
STAGES OF
SLEEPThe typical stages of
snoozing are N 1 (when
you’re barely dozing); N 2 and
N 3 (light and deep sleep,
also called slow-wave sleep,
respectively); and REM,
which stands for “rapid eye
movement” because your eyes
remain active while most of
your other muscles relax.