Seeing the Light of Day
Oh, the light! The autumn light! Is there anything more glorious than an October
day, awash in the sun's low-slung amber rays?
And yet
. . . perhaps you feel the dread, too. The looming inkiness that, like the tide,
crawls up your legs a little higher each day, turning that honeyed light to
molasses and molasses to muck until you realize, too late, that the birds have
left and the world has gone dark. Dark when you wake up, dark when you go
home.
In
simpler times we slept more in winter, but modern living denies us that luxury.
So increasingly each day, soft-white lights from yonder windows break — along
with halogens, tungstens and compact fluorescents. And when we can't stand it
anymore, we resort to manipulation, declaring that 6 in the morning is now
5.
You got
a problem with that, take it up in the spring.
Now
science is finding that our manhandling of light and time is making us
sick.
Artificial illumination is fooling the body's biological
clock into releasing key wakefulness hormones at the wrong times, contributing
to seasonal fatigue and depression. And daylight saving time, extended by
Congress this year for an extra four weeks, risks dragging even more Americans
into a winter funk.
Much
more than mental health is at stake. Women who work at night, out of sync with
the light, have recently been shown to have higher rates of breast cancer — so
much so that an arm of the World
Health Organization will announce in December that it is classifying shift
work as a "probable carcinogen."
That
will put the night shift in the same health-risk category as exposure to such
toxic chemicals as trichloroethylene, vinyl chloride and polychlorinated
biphenyls (PCBs).
"Electric lights are wonderful, but as with a lot of
other things, we really mess things up," said David Avery,
a psychiatrist at the University
of Washington School of Medicine who studies light's impact on health. "Our
ancestors evolved in a very regular light-dark cycle, and our bodies just work
better that way. But more and more, we are creating very irregular, erratic
lighting cues."
Researchers have long known that virtually all living
organisms have biological rhythms that are linked to light. But the human health
implications remained opaque until the 1970s, when scientists discovered the
brain's internal clock: the suprachiasmatic nucleus (SCN), a tangle of neurons
in the hypothalamus connected directly to the eyes.
The SCN
controls the ebb and flow of hormones that influence sleepiness, alertness and
hunger. Prime among them is melatonin, levels of which rise each evening, easing
the onset of sleep, and then fall before dawn in advance of
awakening.
Rats
whose SCNs are surgically removed become unhinged from time, sleeping at odd
intervals. And when one animal's SCN is transplanted into another's brain, the
recipient takes on the donor's wake-sleep schedule.
But the
SCN does not work in a vacuum. It takes its cues from light signals passed along
by the eyes.
For
decades scientists presumed that those clock-setting signals came from rods and
cones, the light-sensitive cells in the retina that provide black-and-white and
color vision. Then, in 2002, researchers at Brown
University discovered an entirely different set of light-detecting cells in
the eyes of humans and other mammals: ganglion
cells.
Unlike
rods and cones, ganglion cells specifically detect sky-blue light. The amount of
light needed to get them firing is about 500 billion photons per second per
square centimeter, or the intensity of sunlight reaching the eye at about
daybreak. Taken together, those traits make them the perfect cells to tell the
brain when dawn has arrived, which they do via a dedicated neural conduit to the
SCN.
Unfortunately, this system does not always work like
clockwork.
Because
of genetic differences, many people's clocks are set differently from others'.
In some, the evening melatonin spike is delayed and sleep comes late. Early
awakening is also often difficult for these night owls, perhaps in part because
their melatonin levels have not had time to drop sufficiently by
morning.
Others
have the opposite problem: The clocks in these morning larks run fast compared
with solar clock time, lulling them to sleep early and then awakening them well
before dawn's early light.
Being
out of phase with the natural day-night cycle can take a big toll, causing
fatigue, mood disturbances and depression. But for millions of Americans, these
symptoms become even worse in winter, blossoming into what is in effect a
months-long case of jet lag.
Scientists disagree on the cause of seasonal affective
disorder, or SAD, as it has come to be known. Some focus on winter's late
sunrises, which appear to push various hormone cycles out of phase with the
daily wake-sleep cycle. Others focus on the early sunsets, which may affect the
timing of melatonin production in the brain.
But
while genes clearly play a role (night owls are more often affected), location
also matters.
Recent
work by Thomas White of the New York State Office of Mental Health and Michael
Terman, director of the Center for Light Treatment and Biological Rhythms at
Columbia University Medical Center, has shown that seasonal depression and mood
disorders become more prevalent not only at northern latitudes — not
surprising, as days are shorter there — but also toward the western edges of
time zones, where people remain in darkness almost an hour later each morning
than their same-timed counterparts farther east.
Daylight saving time, which has been stretched this year
to Nov. 4 for a number of reasons, including an effort to save energy,
exacerbates the problem by further delaying the time of sunrise, a key signal
that resets the body's clock each day.
"From
the psychiatric perspective, the extension of daylight saving time this year was
a very bad decision," Terman said. "Our expectation is we will see increased
depression and mood disorders."
The
good news is that treatments for seasonal depression — primarily the use of
bright light, and in some cases melatonin supplements, to reset the body's clock
— can be effective.
For
most people with SAD, the trick is to get bright light exposure first thing in
the morning to simulate an earlier dawn and shift the body clock forward, said
Alfred Lewy, a psychiatrist and chronobiologist at Oregon Health & Science University
in Portland.
For some people, taking 0.3 to 0.5 milligrams of melatonin in the midafternoon
can also help, he added.
For the
minority of SAD sufferers who are larks, light in the early evening can help.
(Some larks may also benefit from melatonin in the morning, keeping in mind that
even small doses can make some people sleepy.)
Diagnosing yourself as owl or lark can be tricky.
Wake-up times are affected by much more than your natural clock (whether your
sixth-grade daughter has to be fed before trudging off to school in the dark,
for example), so your sleep schedule is not a surefire clue. Lewy suggests
trying morning light first, but switching to the lark regimen if symptoms
worsen.
Many
kinds of lights are available for SAD treatment. Although some experts recommend
those rich in the sky-blue wavelengths (the color that ganglion cells respond
to), others warn that intense blue light can damage the eye. Most research
indicates that 30 to 90 minutes' exposure to fluorescent "white" lighting of
about 10,000 lux works fine, ideally with a plexiglass diffuser to filter
ultraviolet rays and dissipate glare.
So
effective is light as a mood improver that many psychiatrists now suspect that
their understanding of depression has been backward: The disturbed sleep and
withdrawal into darkened rooms so often seen in patients with depression,
bipolar disorder and related problems may be not a symptom of those diseases but
a cause. Reset the clock, and the depression lifts.
A 2005
review commissioned by the American
Psychiatric Association concluded that daily exposure to bright light was
about as effective as antidepressants against several forms of
depression.
Recent
studies have suggested that light therapy can also help patients with
Alzheimer's disease. "They have these random sleep and rest and activity
patterns throughout the day," said Mark Rea, director of the Lighting Research
Center at Rensselaer
Polytechnic Institute in Troy, N.Y. When Rea and colleagues gave Alzheimer's
patients daily doses of blue light at about the intensity of a standard
fluorescent bulb, the patients' ability to sleep through the night was
significantly enhanced.
Blue
light also looks promising for its ability to induce alertness, said Mariana
Figueiro, a program director at the Rensselaer research center. She is testing
the light on submariners, who have trouble remaining vigilant because their
biological clocks don't get cued to dawn and dusk.
Of
course, the fact that artificial lighting can reset people's clocks and boost
alertness at night speaks to its potential to throw normal rhythms into
disarray. As though it were not bad enough that lighting is a 24-7 feature of
modern life, said Avery of the University of Washington, people spend evenings
staring at their "Microsoft blue" computer monitors, then
wonder why they can't fall asleep.
"We've
deseasonalized ourselves," said Thomas Wehr, a psychiatrist at the National
Institute of Mental Health in Bethesda.
"We are living in an experiment that is finding out what happens if you expose
humans to constant summer day lengths."
The
perfect solution, as any camper knows, is to give up artificial light, an
approach that quickly brings one into a cycle of long, restful nights and easy
awakenings at dawn. More realistically, experts recommend avoiding bright lights
after dusk and perhaps wearing yellow sunglasses at brightly lit evening events
to filter out the blue light that might fool your ganglia into thinking it is
morning.
For
those working at night, "the idea might be to have a work environment where at
the beginning of the shift the lighting is heavier in blues that suppress
melatonin, then gradually it changes and becomes redder and redder," a hue that
does not stimulate the eye's ganglion cells, said Richard Stevens, an
epidemiologist at the University of Connecticut Health Center in Farmington.
Stevens
knows how important night-shift lighting can be. It was his focus on the issue
that helped reveal that women who work night shifts for 20 to 30 years have
breast cancer rates 30 to 80 percent higher than their day-shift counterparts.
The mechanism is still not fully explained, but studies have since shown that
melatonin — whose secretion is suppressed by nighttime illumination — is a
potent anticancer hormone.
Consistent with that, profoundly blind women also have
very low rates of breast cancer, presumably because their melatonin levels are
never suppressed by light.
A panel
of experts convened this month by the International Agency for Research on
Cancer, part of the World Health Organization, reviewed studies on animals that
were kept awake at night or subjected to repeated six-hour jet lags, and several
large human studies of nurses and airline flight attendants. It concluded there
is strong evidence that shift work can cause
cancer.
The
agency's pending declaration that shift work is a probable carcinogen may not
have immediate impacts, said Vincent Cogliano, who leads the IARC Monographs
program. "But our findings are looked at by government agencies and scientific
researchers and could stimulate additional
studies."
It may
also send workplace lighting officials into a
quandary.
"Should
we use bluish lights in night-shift work to get the alertness, or avoid it for
its potential to cause cancer?" asked John Bullough of the Rensselaer center,
whose research has focused on the conflicting lighting needs of hospitalized
infants, who seem bothered by bright lights, and their nurses, who need good
lighting to see what they're doing.
The
timing, color and intensity of light are not the only variables that affect
people's health. Several studies have found that the subtle flicker common in
fluorescent bulbs, especially older, low-frequency bulbs with magnetic ballasts,
can have detrimental effects, even though that flicker is just below most
people's threshold of conscious perception.
Stories
that the flicker can trigger seizures are more legend than fact, said Arnold
Wilkins, director of the Visual Perception Unit at the University of Essex in England.
But fluorescent flicker can interfere with eye muscle control while scanning
text or images, he said, and can cause eyestrain and
headaches.
Flicker
is not a problem with the new compact fluorescents, though some are painfully
heavy on glare. The real revolution in lighting, many experts agree, is in the
form of light-emitting diodes, or LEDs, which can be tuned to any color. As they
become more affordable, many say, light will become a bona fide tool for
manipulating health and mood.
Until
then, people struggling to get through the winter will for the most part be best
off sinking obligingly into the long, gray flannel night and avoiding the
midnight lighting they think they crave.
Darkness doesn't have to be about depression and
loneliness, said Dave Crawford, executive director of the International Dark-Sky
Association, a Tucson-based
nonprofit group that advocates against unnecessary
illumination.
It can
be about stars, about contemplation, about quiet conversation with a
friend.
"If we
sprayed water all over the place here in the desert, we'd be put in jail. So why
is it okay to spray light all over the place at night?" asked Crawford, adding
that more than half of all mammals spend most of their waking hours at night or
twilight, "including teenagers."
Light
is fine — in the day — Crawford said. "We're trying to bring to everyone's
attention that there is a night."
For the
next few months, that is going to be hard to forget.
