According to a study, sleeping with even a tiny amount of
light can harm your health.
A new study found that sleeping for only one
night with dim light, such as a TV set with the sound off, raised the blood
sugar and heart rate of healthy young people participating in a sleep lab
experiment.
Even though participants slept with their eyes
closed, dim light entered the eyelids. According to research author Dr. Phyllis
Zee, it disrupted sleep, director of the Center for Circadian and Sleep
Medicine at Northwestern University Feinberg School of Medicine.
Heart rate typically drops at night, slowing
down as the brain repairs and rejuvenates the body. Numerous studies have found
that a higher heart rate at night is a risk factor for future heart disease and
death.
High blood sugar levels are a sign of insulin
resistance. Insulin resistance can progress to Type 2 diabetes over time. The
body stops using glucose properly, and the pancreas goes into overdrive,
flooding the body with extra insulin to overcompensate until it eventually
loses its ability to do so.
Sleeping with eyes closed
Prior research has shown an association between
artificial light at night and weight gain and obesity, disruptions in metabolic
function, insulin secretion and the development of diabetes, and cardiovascular
risk factors.
"Why would sleeping with your lights on
affect your metabolism? Could that explain why there is a higher prevalence of
diabetes or obesity (in society)?" Zee asked.
Zee and her team took 20 healthy people in their
20s and had them spend two nights in a sleep lab. The first night was spent in
a darkened room where "you wouldn't be able to see much, if anything when
your eyes were open," Zee said.
All of the study participants were connected to
devices monitoring several objective measures of sleep quality. So data could
be gathered with minimal interference, they slept with an IV with long tubes
that snake across the room and through a hole to the researcher's side of the
lab. The blood was drawn without ever touching the slumbering participants.
"We recorded the brainwaves and were able
to identify the person's sleep stage," Zee explained. "While they
were sleeping, we recorded their breathing, heart rate, and EKG, as well as
taking blood to test melatonin levels." Melatonin is a hormone that
regulates the body's circadian rhythm or sleeps and wakes the body clock.
A randomized portion of the group repeated that
same light level for a second night in the lab. In contrast, another group
slept with a dim overhead light with a glow roughly equivalent to "a very,
very dark, cloudy day or street lights coming in through a window," Zee
said.
She explained, "Now these people sleep with
their eyelids closed." "According to the research, about 5% to 10% of
the light in the environment would get through the closed lid to the eye, so
it's not much light."
Yet even that tiny amount of light created a
deficit of slow-wave and rapid eye movement sleep, the stages of slumber in
which most cellular renewal occurs, Zee said.
In addition, the sympathetic (fight or flight)
and parasympathetic (rest and relax) nervous systems were unbalanced, linked to
higher blood pressure in healthy people.
The light, however, was not bright enough to
reduce melatonin levels in the body, according to Zee. The study was published
in the Proceedings of the National Academy of Sciences on Monday.
What to do?
What advice would Zee give people based on her
study and existing research in the field? Close your blinds and curtains, turn
off all the lights, and consider using a sleep mask.
"I think the evidence is strong enough that
you should pay special attention to the light in your bedroom," she said.
"Start dimming your lights at least an hour or two before going to bed to
get your environment ready for sleep."
Check your bedroom for sources of light that are
unnecessary, she added. If a night light is needed, she suggests keeping it dim
and at floor level "so that it is more reflected rather than right next to
your eye or bed level."
Also, be aware of the type of light you have in
your bedroom, she added, and ban any lights in the blue spectrum, such as those
emitted by electronic devices like televisions, smartphones, tablets, and
laptops.
"The most stimulating type of light is blue
light," Zee said. "If a light is needed for safety reasons, change
the color. Lights with much more reddish or brownish tones should be
chosen."
LED lights can be purchased in any color, including red and brownish tones.