Exposure to light in the hours leading up to bedtime, in
particular, the light from electronic devices and television, may
be affecting your health, including your weight and blood sugar
levels, according to study published in Physiology
Even at levels you may think harmless, light exposure at night
can trigger a number of health problems, says Dr Kathryn Russart, a
researcher at Ohio State University Wexner Medical Center in
She recently reviewed numerous scientific studies that looked at
the effects of light at night on human health.
Time to Tone Down Blue Light from
Light at night, she says, is an ''environmental endocrine
While many are familiar with chemical endocrine disrupters,
such as PCBs, pesticides, and bisphenol, all of which have been
linked to health problems as well as increased cancer risk, Dr
Russart is focusing on non-chemical endocrine disrupters.
And the light at night, emitted from our electronics,
unfortunately, plays a starring role.
Our circadian rhythm is geared to 24-hour solar days, and we use
environmental cues, such as light, to keep our body clock in sync,
Dr Russart says.
Among the tasks guided by our circadian clock is to manage a
regular hormonal rhythm in endocrine tissues, which seems to be
thrown off by too much exposure to light at night, making it harder
to fall asleep.
The net result, not enough sleep, but that's not all.
More worrisome, she tells EndocrineWeb, is a
negative impact on blood glucose levels.
For example, we see from the research that light at night ''can
cause weight gain, without an increase in calories, and it can
interfere with metabolic function."
Our circadian rhythm is also influenced by the nightly secretion
of the hormone melatonin, and light at night inhibits the
production of this sleep-promoting hormone, Dr Russart says.
That, in turn, could affect the hormone leptin, otherwise
known as the satiety hormone that signals your brain that you are
full, so when this hormone messaging is thrown off, you gain
As long ago as 1987, experts also suspected a link between light
at night and cancer risk. Since then, several studies have found
links between night shift workers and various cancers, including
breast, prostate and many others, Dr Russart says.
How Much Screen Light is Too
"As low as 5 lux of light [the unit of measure scientists use
for light] at night can disrupt your circadian rhythm," Dr Russart
says, at least from research in animals. To put that in
perspective, a TV or a cell phone held about a foot away from your
face can emit 40 lux.
A full moon gives off about 2 lux.
Whatever the sources of light at night - your TV, other
electronics, working the night shift - it's a potential long-term
health hazard, Dr Russart says.
The research findings that "light at night is disruptive is dead
on accurate," says Dr Elena Christofides, an endocrinologist in
private practice in Columbus, Ohio. "These disruptions have been
well known for some time."
These days, she feels that the evidence is so strong about the
downsides of night light that she advises all patients, not
just those with diabetes, to reduce or avoid light at
Dr Christofides says she especially worries when she sees young
children lost in their screens - often a smartphone and their
computer, even the TV, simultaneously - getting high levels of
light exposure, sometimes well into the night.
Study after study has pointed to the health harms of nighttime
light exposure. "It is consistently showing us the same pattern,"
she says of this latest study.
Dr Christofides suggests that you use blue light blocking
glasses, widely sold online, to reduce the exposure to the blue
light from electronics (it also naturally comes from sunlight,
which keeps us going during the day).
"My advice is to put the special glasses on around dinner time
and keep them on as long as you (and your kids) are using the
computer, using your smartphone, on the iPad, and watching TV. The
aim is to block out the bluewave-type light, which can make it
harder to get to sleep," she says.
If you go out to dinner, you can leave the glasses behind, she
The greatest need is at home when people are typically on the
computer, on their handheld devices, and watching television, in
the hours leading up to bedtime, she says.
Not everyone agrees the blue light-blocking glasses work, but
the data is growing and experts do say health problems can
result from too much exposure to blue light before bed.
The effects of the light exposure on your health happen slowly,
and are cumulative, Dr Christofides says, so the effects may not be
readily apparent. Nor do people connect light exposure with their
"When they gain weight or their blood sugar goes up, and she
suggests it might be the light at night and impact on sleep; 'they
cannot imagine their lifestyle is to blame," she says.
"Disruption of the normal nocturnal rhythm will end badly," she
tells her patients.
Based on the evidence, Dr Russart adds: "I do think if
someone already has diabetes or prediabetes, they should be
particularly interested [in the research] and take particular
Choosing your electronics carefully also may help, Dr Russart
says. "The part of the eye that is affected by light is stimulated
in particular by the blue wavelength," she says. "Many phones have
built-in apps to lessen some of the blue light."
And try to limit screen exposure in the 2 to 3 hours right
To improve sleep, experts also suggest:
- Avoid using electronics in the hours before bed.
- Be sure your bedroom is dark; use heavy window shades if
- Consider a sleep mask.