Even moderate light exposure during sleep harms heart health and increases insulin resistance
From: Northwestern University
March 14, 2022 -- Exposure
to even moderate ambient lighting during nighttime sleep, compared to sleeping
in a dimly lit room, harms your cardiovascular function during sleep and
increases your insulin resistance the following morning, reports a new study.
Just a single night of exposure to moderate room lighting during sleep can
impair glucose and cardiovascular regulation, which are risk factors for heart
disease, diabetes and metabolic syndrome.
"The results from
this study demonstrate that just a single night of exposure to moderate room
lighting during sleep can impair glucose and cardiovascular regulation, which
are risk factors for heart disease, diabetes and metabolic syndrome," said
senior study author Dr. Phyllis Zee, chief of sleep medicine at Northwestern
University Feinberg School of Medicine and a Northwestern Medicine physician.
"It's important for people to avoid or minimize the amount of light
exposure during sleep."
There is already
evidence that light exposure during daytime increases heart rate via activation
of the sympathetic nervous system, which kicks your heart into high gear and
heightens alertness to meet the challenges of the day.
"Our results
indicate that a similar effect is also present when exposure to light occurs
during nighttime sleep," Zee said.
The study will be
published March 14 in PNAS.
Heart rate increases in
light room, and body can't rest properly
"We showed your
heart rate increases when you sleep in a moderately lit room," said Dr.
Daniela Grimaldi, a co-first author and research assistant professor of
neurology at Northwestern. "Even though you are asleep, your autonomic
nervous system is activated. That's bad. Usually, your heart rate together with
other cardiovascular parameters are lower at night and higher during the
day."
There are sympathetic
and parasympathetic nervous systems to regulate our physiology during the day
and night. Sympathetic takes charge during the day and parasympathetic is
supposed to at night, when it conveys restoration to the entire body.
How nighttime light
during sleep can lead to diabetes and obesity
Investigators found
insulin resistance occurred the morning after people slept in a light room.
Insulin resistance is when cells in your muscles, fat and liver don't respond
well to insulin and can't use glucose from your blood for energy. To make up
for it, your pancreas makes more insulin. Over time, your blood sugar goes up.
An earlier study
published in JAMA Internal Medicine looked at a large population of healthy
people who had exposure to light during sleep. They were more overweight and
obese, Zee said.
"Now we are
showing a mechanism that might be fundamental to explain why this
happens," Zee said. "We show it's affecting your ability to regulate
glucose."
The participants in the
study weren't aware of the biological changes in their bodies at night.
"But the brain
senses it," Grimaldi said. "It acts like the brain of somebody whose
sleep is light and fragmented. The sleep physiology is not resting the way it's
supposed to."
Exposure to artificial
light at night during sleep is common
Exposure to artificial
light at night during sleep is common, either from indoor light emitting
devices or from sources outside the home, particularly in large urban areas. A
significant proportion of individuals (up to 40%) sleep with a bedside lamp on
or with a light on in the bedroom and/or keep the television on.
Light and its
relationship to health is double edged.
"In addition to
sleep, nutrition and exercise, light exposure during the daytime is an
important factor for health, but during the night we show that even modest
intensity of light can impair measures of heart and endocrine health," Zee
said.
The study tested the
effect of sleeping with 100 lux (moderate light) compared to 3 lux (dim light)
in participants over a single night. The investigators discovered that moderate
light exposure caused the body to go into a higher alert state. In this state,
the heart rate increases as well as the force with which the heart contracts
and the rate of how fast the blood is conducted to your blood vessels for
oxygenated blood flow.
"These findings
are important particularly for those living in modern societies where exposure
to indoor and outdoor nighttime light is increasingly widespread," Zee
said.
Zee's top tips for
reducing light during sleep
(1) Don't turn lights
on. If you need to have a light on (which older adults may want for safety),
make it a dim light that is closer to the floor.
(2) Color is important.
Amber or a red/orange light is less stimulating for the brain. Don't use white
or blue light and keep it far away from the sleeping person.
(3) Blackout shades or
eye masks are good if you can't control the outdoor light. Move your bed so the
outdoor light isn't shining on your face.
Is my room too light?
"If you're able to
see things really well, it's probably too light," Zee said.
Other Northwestern
authors are co-first author said co-first author Ivy Mason, who at the time of
the study was post-doctoral fellow at Northwestern and now is a research fellow
at Harvard Medical School, Kathryn Reid, Chloe Warlick, Dr. Roneil Malkani and
Dr. Sabra Abbott.
The research was
supported, in part, by the National Center for Advancing Translational Sciences
grant 8UL1TR000150-05, National Heart, Lung, and Blood Institute grant R01
HL140580, National Institute of Aging grant P01AG11412, all of the National
Institutes of Health, and the American Heart Association.
https://www.sciencedaily.com/releases/2022/03/220314154355.htm
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