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The Psychiatry of Light
“You don’t hear a psychiatrist asking how much light you get,” Satchin Panda told
a reporter for The Economist (1). “It affects so much of our physiology, psychology, and
mood. But we take it for granted.” Panda is a scientist at the Salk Institute who first
identified melanopsin (a photopigment found in non-visual retinal ganglion cells) as the
primary light receptor for the regulation of circadian rhythm. He is an expert in the
biology of light. He also recognizes how little the rapidly expanding body of knowledge
about light and health has affected psychiatric practice, to the detriment of our patients.
In contrast to both medications and psychotherapy, there is remarkably little data
on the use of bright light therapy by psychiatrists or other mental health clinicians in the
United States (2), an absence that itself reflects a lack of attention to the clinical use of
light. The first survey we know of has just been published, an email survey of
Massachusetts psychiatrists (3). 72% of the psychiatrists who responded sometimes
recommend the use of bright light – most often for seasonal affective disorder, much less
frequently for non-seasonal depression, and rarely for inpatients. As the authors’ point
out, a very low response rate to the survey (14%) likely led to an overestimation of the
actual use of bright light therapy in clinical practice.
This impression is certainly confirmed by conversations we have had with a wide
range of colleagues. “Is there really evidence for its effectiveness in depression?” is a
response we hear surprisingly often from otherwise up-to-date psychiatrists. Before
reviewing the evidence of effectiveness in depression and other syndromes, it is worth
considering why an “evidence-based” treatment with an unusually benign side effect
profile remains in the shadows.
With obvious parallels to psychotherapy, the lack of industry-based funding to
supplement federal research grants has slowed the emergence of a compelling body of
research on light-based treatments, and the lack of industry-based funding for advertising
and speakers slows the dissemination of research findings to clinicians. Yet in contrast to
psychotherapy, bright light therapy lacks a large and established group of practitioners
ready to enthusiastically “rebroadcast” news of positive research results.
Other possible reasons have more to do with the nature of bright light therapy
itself. Unlike swallowing a pill, it requires time. The use of artificial light tethers a patient
to a light box. The use of natural light stirs concerns about UV exposure. Absent an
understanding of the importance of circadian rhythm to most bodily functions and
behaviors, along with an understanding of the importance of light to circadian rhythm,
light therapy can seem on the “alternative” margins of scientific medicine. And light just
sounds less potent and less precise than a medication. We will return to these questions,
which are extremely important in clinical practice, after a non-exhaustive review of the
evidence that supports more widespread use of light therapy in psychiatric care.
Bright Light Therapy for Affective Disorders
The therapeutic use of bright light in psychiatry began in 1984 with a
groundbreaking study published by a group at the NIMH that first described “seasonal
depression” and the use of bright light as an effective antidepressant in 11 patients (4). In
2005, the American Psychiatric Association Council on Research convened a work group
2
to review the subsequent 20 years of research on light therapy for the treatment of
depression. The number of studies that met their rigorous inclusion criteria was small (8
for seasonal and 3 for nonseasonal depression), but they concluded that light therapy was
an effective treatment not only for seasonal depression (SAD) but for nonseasonal
depression (5). Notably, the effects sizes for light therapy were “equivalent to those in
most antidepressant pharmacotherapy trials” (0.84 for SAD, 0.53 for nonseasonal
depression).
Subsequent research has supported, refined and extended these conclusions (6). A
“gold standard” treatment approach has emerged, using a fluorescent light box that
produces 10,000 lux of white light at a specified distance from the user’s eyes, beginning
with 30 minutes exposure in the early morning, as close to awakening as feasible (7). A
dose-response curve has been defined, with a threshold of 2500 lux for an antidepressant
effect. Two hours of exposure are required at 2500 lux and 45-60 minutes at 5000 lux.
There seems to be no further reduction in time required for efficacy at light intensities
greater than 10,000 lux (a bright sunny day can reach intensities of 50,000-100,000 lux).
At the other end of the brightness curve, it is important to note that, other than sitting in a
window with sunshine streaming in, indoor lighting, however bright it may seem (our
eyes adjust very effectively to immense variations in brightness), never approaches 2500
lux. Treatment parameters are adjusted based on individual response. Terman reports
that remission rates in SAD can be improved by timing the treatments to an individual’s
evening melatonin onset, using a self-rating scale called the Morningness-Eveningness
Questionnaire (MEQ) as a rough proxy for salivary melatonin assays (8). There is
preliminary evidence that SAD patients have a less sensitive light input pathway related
to variations in the melanopsin gene (9), which opens up the possibility of more
fundamental and individualized approaches to dosing in the future.
The key pathway for light’s role as primary time-keeper for circadian rhythm
begins with melanopsin-containing intrinsically photosensitive retinal ganglion cells
(ipRGCs), which project to the suprachiasmatic nuclei of the anterior hypothalamus, the
body’s master biological clock. The peak spectral sensitivity of the system is 460 nm, in
the blue range. Two studies by the same group found low-intensity blue-enriched light
(750 lux) as effective but not superior to standard bright light (10,000 lux) in treating
SAD (10,11). Most experts still recommend white light, however, since the evidence base
is much better established and the interplay of effects of differing wavelengths is complex
and not yet fully understood (6; pp 54-55).
The identification of melanopsin and the associated neural pathways has had
profound theoretical and practical implications for the use of light therapy. It may not be
the whole story however. One of the more intriguing hypotheses is humoral
phototransduction, in which blood-borne hemoglobin and bilirubin in the central retinal
vein act as photoreceptors and the resulting release of carbon monoxide serves as a signal
and regulator of circadian and seasonal changes (12). These ongoing investigations, along
with lingering questions about a role for the visual rod and cone receptors in circadian
regulation, may further refine our understanding of optimal spectra for light therapy.
The APA work group found no evidence for improved response from the
combination of bright light and antidepressant medication, but well-designed trials not
available at the time show both superior response and remission rates over medication
3
treatment alone in non-seasonal major depressive disorder (13). The combination of wake
therapy (sleep deprivation at the start of treatment), bright light therapy, and medication
is emerging as a particularly effective strategy in both major depressive disorder (14,15)
and bipolar depression (16,17). A recent study combining lithium with sleep deprivation
and light therapy showed not only rapid improvement but an immediate and persistent
decrease in suicidality after the first sleep deprivation cycle (18). Bright light treatment
carries a low but significant risk of switching in bipolar depression. A small study
suggests that initiating treatment with midday rather than the usual early morning light
may minimize that risk (19). Conversely, a pilot study of “dark therapy” (light
deprivation) in acute mania suggests it may lead to more rapid improvement when added
to standard treatments(20).
In other specialized patient populations, studies have shown bright light treatment
to be an effective treatment for nonseasonal major depression in the elderly (21,22) and a
promising treatment in perinatal depression (23).
Bright Light Therapy for Other Psychiatric Disorders
Bright light therapy has a conceptually straightforward and well supported role in
the treatment of circadian rhythm sleep disorders, disturbances in sleep that result from a
misalignment of an individual’s sleep-wake pattern with his or her internal circadian
system or with the demands of the external world (24). The major categories are delayed
sleep-phase disorder, advanced sleep-phase disorder, jet lag disorder, shiftwork disorder,
and free-running disorder in blind patients (some individual’s with blindness are still
responsive to light as a circadian regulator through the melanopsin-SCN pathway). Early
morning light is used to phase advance an individual’s sleep-wake cycle and late
afternoon/evening light to phase delay the cycle. Lose dose melatonin can also be used
with the opposite timing – early morning for phase delay and late afternoon/evening for
phase advance (25).
Beyond improving the immediate consequences of insomnia (fatigue, decreased
performance in both cognitive and motor tasks, decreased alertness), the treatment of
circadian rhythm sleep disorders links back to the treatment and prevention of mood
disorders. There appears to be a fundamental connection between phase-delay of internal
circadian rhythm and mood disturbances (25), so the effectiveness of similar
interventions (bright light and melatonin) in both conditions is not surprising. There is
also evidence that poor sleep in the elderly is a “considerable” risk factor for suicide over
a subsequent 10 year period independent of the presence of other depressive symptoms
(26.) Attention deficit/hyperactivity disorder (ADHD) is another condition in which
there is emerging evidence for improvement from exposure to bright light. An intriguing
study looked at the relationship between the prevalence of ADHD and solar intensity
(kilowatt hour/square meters/day), both across nations and, in the United States, across
states. Higher solar intensity was strongly associated with a lower prevalence of ADHD
in both children and adults (27). An open trial of bright light therapy in adult ADHD had
positive results (28.) And returning to circadian issues, a recent small pilot study found
evidence for sleep disruption, phase delays, unstable circadian rhythms, and seasonal
effects on circadian rhythm stability and symptomatology in ADHD (29).
4
Given the importance of circadian rhythms to optimal function in “normal” states,
there is currently a paucity of research on the effect of bright light enhancement in non-
clinical populations. Since modern life carries with it a notable reduction in exposure to
bright light (see below), we expect more research to be emerging. There is evidence that
bright light treatment “improves vitality and alleviates distress” in healthy office
employees during winter months (30), that bright light has important alerting effects apart
from the treatment of disordered states (31), and that these alerting effects directly
improve cognitive function (32). The latter study also suggests a new complexity to the
system, with the response to a test dose of light affected by the wavelength of light to
which individuals were exposed prior to the test (“photic memory”). Finally, a large study
of healthy older women (median age 67) found that increased light exposure was
associated with improved quality of life and both social and emotional functioning (33).
Bright Light Therapy for Medical/Psychiatric Conditions
Parkinson’s Disease (PD) is an illness closely associated with depression. Patients
with PD are at high risk for depression (34) and depression increases the risk of PD (35).
PD is also associated with circadian desynchronization and several studies have found
that bright light therapy has positive effects not only on sleep and mood in PD patients
but on motor function as well (36).
Circadian desynchronization is also a major problem in Alzheimer’s Disease (AD)
and related dementias. The use of bright light in a small number of studies has shown
mixed results (37). A promising new pilot study that used bluish-white light in the rooms
of nursing home patients with AD found significant improvement in sleep quality,
efficiency, and total sleep time, along with reduced depression and agitation (38). Early
studies of bright light as an adjunctive treatment for hospitalized patients with delirium
have also been encouraging (39,40).
The association between “winter blues” and weight gain raises questions about
the use of bright light for weight loss. A single placebo-controlled, randomized trial found
that morning bright light treatment reduced body fat and appetite in overweight woman
(41). Complicating the picture, there is also evidence that morning bright light improves
efficiency of carbohydrate digestion and absorption from an evening meal and evening
bright light has the opposite effects, which suggests that (unromantic) bright light at
supper could be an aid to weight loss (42,43). A recent and careful correlational study
however finds that exposure to moderately bright light (above 500 lux) earlier in the day
is associated with lower BMIs, independent of effects on sleep (44).
Finally, one of the more intriguing new findings is that bright light (sunlight) in
childhood may be an essential element for healthy eye development. Concern about an
“epidemic” of myopia in urban east Asia (the prevalence of myopia in young adults is
80% (45)), led researchers to investigate a possible associate between myopia,
educational pressure, and time spent outdoors. Not only did a strong correlation emerge
between outdoor time and a lower prevalence of myopia in children (45). A simple
(randomized) program encouraging elementary school children to spend one hour of
daily recess outdoors led to a significant reduction in new-onset cases of myopia by the
end of the school year (46).
5
Contemporary Exposure to Light and Darkness
Over the past century, electric lighting has transformed the relationship between
human activity and the natural cycles of light and darkness in which our physiology
evolved. Most of our days are spent in light that is significantly dimmer than sunlight and
much of our nights are spent in light that is significantly brighter than starlight or
moonlight. As summarized in a 2008 review by Turner and Mainster:
Young adults in industrialized countries typically receive only 20–120 min
of daily light exposure exceeding 1000 lux. Elderly adults’ bright light
exposures average only 1/3 to 2/3 that duration. Institutionalized elderly
receive less than 10 min per day of light exposure exceeding 1000 lux,
with median illuminances as low as 54 lux (47).
The effect of decreasing exposure to bright light in the elderly in amplified by a
dramatic decline in transmittance of light through the eye as we age, the result of both
crystalline lens yellowing and pupillary miosis (47). Compared to a 10 year old, the eyes
of a 45 year old transmit only half the light active in circadian photoreception to the
retina and by 95 years old, it has dropped to one tenth the level of a 10 year old. The
relevance to sleep disorders, mood disorders and cognitive decline in the elderly is a
subject of active investigation.
Wright has begun to examine directly the changes in circadian function that occur
when individuals move from a modern electrically lit “constructed environment” to
natural lighting alone during camping trips with no artificial light sources available. His
findings emphasize that natural sunlight is a more powerful “zeitgeiber” (timing cue) for
circadian rhythm than electric lighting and without it, internal difference in circadian
periodicity express themselves more strongly and move an individual away from a state
of light-based entrainment to the 24 solar day (48).
At the other end of the day, the ubiquitous presence of electric light and
illumination from electronic screens (which emit significant amounts of blue light at the
peak sensitivity of ipRGCs) has captured public attention (49). The upper limits of
nighttime illumination that do not disrupt circadian function is unclear, but there are
suggestions that remarkably low levels can have significant effects (50). Light-based
nighttime disturbances of circadian rhythm and melatonin secretion may not only lead to
sleep and mood problems, but have also been associated with increased risk for breast
cancer and intrinsic resistance to tamoxifen therapy in breast cancer (51). Technology can
also help with this problem. For patients who cannot avoid exposure to light from
computer and smart phone screens as bedtime approaches, there are now programs and
apps that will gradually red-shift the screen illumination based on time of day (like the
free program f.lux).
Adverse Effects
Like all effective treatments of depression, bright light therapy can trigger a shift
to mania or hypomania in patients with bipolar depression. Otherwise, immediate side
6
effects are mild and can usually be managed by temporary reductions in light intensity or
duration. Most common are reports of eye discomfort, headache, and feeling “wired”
(7,pp33-35).
Long-term exposure to solar UVB radiation is associated with an increased risk of
cataract formation. Therapeutic light boxes effectively filter out all UV light. For patients
using natural light, the UV component of sunlight is low in the early morning hours,
when bright light treatment is optimal for most patients. Eye protection in the form of
sunglasses and brimmed hats is recommended only during the middle of the day (52). A
new retrospective study shows an association between lifetime solar exposure and
exfoliation syndrome (XFS), a form of ocular aging associated with increased risk for a
number of deleterious conditions, including cataract formation (53). The researchers
asked subjects about time outdoors only between the hours of 10 AM and 4 PM,
presumably positing the safety of early morning sunlight. (Supporting the importance of
eye protection during the middle of the day when UV radiation is high, sunglasses were
protective in the US but not Israel and brimmed hats were not protective at all, perhaps
because of significant reflected UV radiation.) Since bright light therapy works through
the eyes, protecting the skin from solar radiation does not reduce its efficacy.
Most manuals on light treatment offer cautions about its use in patients with
underlying retinal disease, suggesting guidance from an ophthalmologist, with baseline
and annual follow-up eye exams (6, p57; 7,p37). Patients with age-related macular
degeneration (AMD) are regularly cautioned against unprotected exposure to sunlight and
environmental light exposure has long been suspected to be a risk factor in AMD. A
current review however concludes that decades of research does not support the view that
environmental light is a significant factor in AMD (54).
Patients on photosensitizing medications, including phenothiazines, lithium, and
St. Johns wort, should similarly be assessed before treatment and followed with regular
eye exams. Melatonin also causes retinal photosensitization but can safely be combined
with bright light therapy when used correctly, since it should be administered at the
opposite end of the day from light therapy and has a short half life (6, p 57).
In our own practices, the “side effect” that most often leads patients to discontinue
light therapy is that it requires time. A typical comment from one patient: ”If you think
my kids and wife will let me sit at the table in front of a light box while everyone else is
getting ready for school or work, you just don’t understand my life.” By contrast, it only
takes a moment to take a pill. The possibility of better engineering of indoor light both in
the workplace and the home, as well as the use of wearable sensors to “dose” natural light
may eventually minimize these practical obstacles to the use of bright light therapy.
Conclusions
Our own experience with the use of light therapy began in the mid-1980s, soon
after the publication of the earliest studies on SAD. In the absence of commercially
manufactured light boxes, a colleague down the hall had drawn up a shopping list and
instructions that let patients build their own with parts from their local hardware store.
Our colleague soon withdrew his instructions from circulation because of liability issues
(so we will sadly not give credit for his work), but fortunately a commercial light box
soon became available from a company started by someone who was participant in the
7
original NIMH study and was appalled to find that there was no way for him to continue
an effective treatment once the study was over. We have been fascinated to follow the
emergence of research over the past three decades that has not only extended our
understanding of the use of light in psychiatry but helps us to appreciate the complex
effects of light on circadian and seasonal regulation, the importance of circadian
regulation in an expanding array of functions at both the cellular and organismic levels,
and the unanticipated health effects from the transformation of our daily relationship to
light in a modern “constructed environment.”
The story continues to emerge. Along the way, a better integration of the
psychiatry of light and the indications for bright light therapy into the “standard”
education of psychiatrists offers many benefits to our patients. It is not a panacea. The
history of psychiatry is strewn with the overselling of a favorite approach to treatment.
But bright light therapy can be both effective and uncommonly safe. It deserves more
attention and more frequent use.
8
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