Can staying up late make you fat? A growing body of research has
suggested that poor sleep quality is linked to an increased risk of obesity by
deregulating appetite, which in turn leads to more calorie consumption.
But a new study published this week in PLOS Biology found that the
direction of this reaction might actually be flipped: It’s not the sleep loss
that leads to obesity, but rather that excess weight can cause poor sleep,
according to researchers from the University of Pennsylvania’s Perelman School
of Medicine and the University of Nevada, Reno, who discovered their findings
in the microscopic worm Caenorhabditis elegans (C.
elegans).
“We think that
sleep is a function of the body trying to conserve energy in a setting where
energetic levels are going down. Our findings suggest that if you were to fast
for a day, we would predict you might get sleepy because your energetic stores
would be depleted,” said study co-author David Raizen, MD, PhD, an associate
professor of Neurology and member of the Chronobiology and Sleep Institute at
Penn.
Raizen emphasized that while these findings in worms may not translate
directly to humans, C. elegans offer a
surprisingly good model for studying mammalian slumber. Like all other animals
that have nervous systems, they need sleep. But unlike humans, who have complex
neural circuitry and are difficult to study, a C. elegans has only 302
neurons — one of which scientists know for certain is a sleep regulator.
In humans, acute
sleep disruption can result in increased appetite and insulin resistance, and
people who chronically get fewer than six hours of sleep per night are more
likely be obese and diabetic. Moreover, starvation in humans, rats, fruit
flies, and worms has been shown to affect sleep, indicating that it is
regulated, at least in part, by nutrient availability. However, the ways in
which sleeping and eating work in tandem has remained unclear.
“We wanted to
know, what is sleep actually doing? Short sleep and other chronic conditions,
like diabetes, are linked, but it’s just an association. It’s not clear if
short sleep is causing the propensity for obesity, or that the obesity,
perhaps, causes the propensity for short sleep,” said study co-author Alexander
van der Linden, PhD, an associate professor of Biology at the University of
Nevada, Reno.
To study the association between metabolism and sleep, the researchers
genetically modified C. elegans to “turn off” a
neuron that controls sleep. These worms could still eat, breathe, and
reproduce, but they lost their ability to sleep. With this neuron turned off,
the researchers saw a severe drop in adenosine triphosphate (ATP) levels, which
is the body’s energy currency.
“That suggests
that sleep is an attempt to conserve energy; it’s not actually causing the loss
of energy,” Raizen explained.
In previous research, the van der Linden lab studied a gene in C.
elegans called KIN-29. This gene is homologous to the
Salt-Inducible Kinase (SIK-3) gene in humans, which was already known to signal
sleep pressure. Surprisingly, when the researchers knocked out the KIN-29 gene
to create sleepless worms, the mutant C. elegans accumulated excess
fat — resembling the human obesity condition — even though their ATP levels
lowered.
The researchers
hypothesized that the release of fat stores is a mechanism for which sleep is
promoted, and that the reason KIN-29 mutants did not sleep is because they were
unable to liberate their fat. To test this hypothesis, the researchers again
manipulated the KIN-29 mutant worms, this time expressing an enzyme that
“freed” their fat. With that manipulation, the worms were again able to sleep.
Raizen said this
could explain one reason why people with obesity may experience sleep problems.
“There could be a signaling problem between the fat stores and the brain cells
that control sleep,” he said.
While there is
still much to unravel about sleep, Raizen said that this paper takes the
research community one step closer to understanding one of its core functions —
and how to treat common sleep disorders.
“There is a
common, over-arching sentiment in the sleep field that sleep is all about the
brain, or the nerve cells, and our work suggests that this isn’t necessarily
true,” he said. “There is some complex interaction between the brain and the
rest of the body that connects to sleep regulation.”
Source: https://myfusimotors.com/2020/04/25/link-between-obesity-and-sleep-loss/
