“How to Sync Your Central Circadian
Clock to Your Peripheral Clocks”
One of the most important
breakthroughs in recent years
has been the discovery
of peripheral clocks.
We’ve known about the central clock,
the so-called suprachiasmatic nucleus,
for decades. It sits in the middle
of your brain right above
where your optic nerves cross,
allowing it to respond to night and day.
Now we know there are semi-autonomous
clocks in nearly every organ in our body.
Our heart runs on a clock, our lungs run
on a clock, our kidneys run on a clock.
Up to 80% of the genes in our liver
are expressed in a circadian rhythm.
Our entire digestive tract does too.
The rate at which our stomach empties,
the secretion of digestive enzymes,
and the expression of transporters
in our intestinal lining
for absorbing sugar and fat
all cycle around the clock.
So too does the ability of our
body fat to sop up extra calories.
The way we know these cycles are
driven by local clocks, rather than
being controlled by our brain, is that
you can take surgical biopsies of fat,
put them in a petri dish, and
still watch them rhythm away.
All this clock talk is not
just biological curiosity.
Our health may depend on
keeping all these clocks in sync.
Think about it like a child
playing on a swing.
Imagine you’re pushing, but you
become distracted by other goings-on
in the playground and stop
paying attention to your timing.
So you forget to push, or
push too early, push too late.
What happens? Out of sync, the swinging
becomes erratic, slows, or even stops.
That is what happens when we
travel across multiple time zones
or have to work the night shift.
The pusher in this case are
the light cues falling on our eyes.
Our circadian rhythm is meant to get a
bright light push every morning at dawn,
but if the sun rises at a different time
or we’re exposed to bright light
in the middle of the night, this
can push our cycle out of sync
and leave us feeling out of sorts.
That’s an example of a mismatch
between the external environment
and our central clock.
Problems can also arise from a
misalignment between the central clock
in our brain and all the other organ
clocks throughout our body.
An extreme illustration of this is
a remarkable set of experiments
suggesting even our poop can get jetlag.
Our microbiome seems to
have its own circadian rhythm.
Even though they’re down where the
sun don’t shine, there’s a daily oscillation
in both bacterial abundance
and activity in our colon.
Interesting, but who cares?
Check this out: if you put people
on a plane and fly them halfway around
the world, then feed their poop to mice,
they grow fatter than mice fed preflight
feces. Though it may have just been
bad airline food or something, the
researchers suggest the fattening
flora was a consequence
of circadian misalignment.
Indeed, several lines of evidence
now implicates chronodisruption—
the state in which our central and
peripheral clocks diverge out of sync—
as playing a role in conditions ranging
from premature aging and cancer,
to mood disorders and obesity.
Bright light exposure
is the synchronizing swing
pusher for our central clock.
Well, what drives our internal organ
clocks that aren’t exposed to daylight?
Food intake. That’s why the timing
of our meals may be so important.
Removing all external timing
cues by locking people away
under a constant dim light, researchers
showed you could effectively decouple
central from peripheral rhythms
just by shifting meal times.
They took blood draws every hour
and even took biopsies of their fat
every six hours to demonstrate
the resulting metabolic disarray.
Just as morning light can help sync
your central clock in your brain,
morning meals can help
sync your peripheral clocks
throughout the rest of your body.
Breakfast skipping disrupts
the normal expression and rhythm
of these clock genes themselves,
which coincides with the
adverse metabolic effects.
Thankfully, they can be reversed.
Take a group of habitual breakfast
skippers, and have them eat
three meals at 8 am, 1 pm, 6 pm, and
their cholesterol and triglycerides
improves, compared to taking meals
five hours later at 1 pm, 6 and 11 pm.
See, there’s a circadian rhythm to
cholesterol synthesis in the body too,
which is also strongly influenced by food
intake, as evidenced by the 95% drop
in cholesterol production in
response to a single day of fasting.
That’s why just a few hours
shift in meal timing can result
in a 20-point drop in LDL cholesterol,
thanks to eating earlier meals.
“How to Sync Your Central Circadian