Even moderate light exposure during sleep harms heart health and increases insulin resistance
Northwestern University
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.
Close
the blinds, draw the curtains and turn off all the lights before bed. 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
Northwestern Medicine study.
"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 was 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.
