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Blue light is associated with a host of physical health maladies, including obesity, diabetes, and cancer. But what does it do to patients with depression or bipolar disorder?
Blue light is getting blamed for everything from eye strain to cancer lately, but what does it do to our patients with depression and bipolar disorder. A lot, as you will see in this podcast, but it depends on what time of day it is shining.
Welcome to PsychPearls podcast with Psychiatric TimesTM, the Voice of Psychiatry. With thoughtful insights into the world of mental health, this podcast provides timely clinical commentary and practical cutting-edge pearls for you and your practice. We hope you enjoy.
I am Chris Aiken, the Mood Disorders Section Editor for Psychiatric TimesTM and the editor-in-chief of the Carlat Psychiatry Report, and I am Kellie Newsome, a psychiatric NP and the cohost of the Carlat Psychiatry Podcast.
KELLIE NEWSOME: The biological clock is set by the daily rhythms of light and dark – morning sunrise and evening sunset. And this clock is so integral to bipolar disorder that you could almost rename it fragile circadian rhythm disorder. Actually, patients prefer that name over bipolar disorder, and it gets to the heart of the problem. Bipolar is tightly linked to the genes that regulate the biological clock, and lithium actually helps repair the clock by altering the expression of those genes.1 Many of the behavioral therapies for bipolar disorder, like dark therapy and social rhythm therapy, also work through the biological clock, helping patients to keep it running smoothly by regulating their exposure to light, darkness, and the timing of daily activities.
But bipolar is not the only mental illness that is linked to disrupted circadian rhythms. Unipolar depression is as well, though to a lesser extent – for example, rates of circadian rhythm disorders like the phase-delay night owl syndrome are more common in bipolar and unipolar, but they are about 20% less common in unipolar. And research is exploring circadian rhythm therapies in borderline personality disorder, substance use disorders, schizophrenia, ADHD, and PTSD.
But while researching is advancing in the circadian direction, society is moving the other way. Indoor living and nocturnal light are dampening the natural signals that set the biological clock, and there is evidence that this is causing harm in our patients. In this podcast, we will explore those dangers, but first a little background on how light – and in particular blue light – set the biological clock.
Blue Light and Melatonin
KELLIE NEWSOME: Light suppresses melatonin, but not just any light. It is the color that matters here, and blue light in the 460-480 nm range is particularly good at suppressing melatonin and promoting wakefulness. In the 1990s, a new photoreceptor called melanopsin was discovered that only responds to blue light, and it is this receptor that regulates melatonin production through the suprachiasmatic nucleus, the time-keeper of the biological clock.2
What that means is that the body’s internal clock depends on strong shifts in blue-spectrum light at the bookends of the day: morning and night. High levels of evening blue light, and low levels in the morning, disrupt not just circadian rhythms but also the clock genes implicated in bipolar and other psychiatric disorders.3,4
The main source of that blue light are electronic gadgets that were not available 20 years ago. Smart phones, LED screens, and energy-efficient bulbs emit a blue haze of light that is very different from the yellow starlight that we evolved under. This light may look white, like fluorescent bulbs, but white light has a lot of the blue wavelength within it. Distance also matters here. A cell phone close to your face emits about as much blue light as a large screen TV across the living room.
CHRIS AIKEN: The problem is not just psychiatric. Blue light is associated with physical health risks including obesity, diabetes, cancer, cardiovascular and neurologic diseases, gastrointestinal ulcers, and adverse reproductive outcomes.5 The American Medical Association released a position statement calling for reductions in nocturnal blue light, and psychiatry is catching on as well. The American Academy of Child and Adolescent Psychiatry updated their pediatric sleep recommendations in 2018. They no longer recommend night lights for anxious children and instead emphasize elimination of blue-light sources in the bedroom. Child psychiatrists in Canada have even stronger recommendations.
KELLIE NEWSOME: It is the young and old that are most vulnerable to these light changes, as we will see in the research here.6,7 But they are also the patients who are more likely to sleep with some lights on. So, if your patient needs a light at night – whether because of a childhood phobia or a fall risk – they can purchase amber nightlights that do not emit the blue wavelength.
A Slightly Broken Biological Clock
CHRIS AIKEN: Psychiatric patients in general are more sensitive to the circadian disrupting effects of evening blue light, particularly patients with bipolar disorder. Melatonin is delayed, diminished, and more easily suppressed by blue light in these patients.6 Circadian disruptions often trigger new episodes of mania and depression, such as shift work, seasonal changes, and travel across multiple time zones.8
KELLIE NEWSOME: Travel across time zones is only a problem with air travel, because the clock has time to adjust when you travel by land or sea unless you are driving at 300 miles per hour. And on average it only causes problems when patients travel across 2 or more time zones. Mania is more common with west to east travel, and depression more likely when travelling east to west. A simple rhyme can help you remember it – west is depressed – because travelling westbound can trigger depression.
CHRIS AIKEN: We can add nocturnal blue light and ambient bedroom light to that list of circadian disruptors. Evening use of smartphones delays and reduces melatonin secretion, and impairs sleep and cognition with a medium effect size (0.5), which means the effect should be noticeable to the casual observer.9 A viscous cycle is at play here, as evening-types (night owls) have a greater tendency to use electronics at night, and that use independently shifts circadian rhythms toward the evening type (phase delay).6,10 The evening chronotype is prominent in adolescents, and being a night owl is a risk factor for bipolar disorder, depression, and substance abuse.8,10
Ambient bedroom light is also a problem, as it passes through the eyelids and suppresses melatonin during sleep. In controlled animal studies, ambient nocturnal light causes depression, impedes learning, and has detrimental effects on the brain. It lowers BDNF and shortens the dendritic spines that are essential for learning and cognition.11
The circadian system is also involved in critical periods of brain development, and disruptions of light signals may play a role in the onset of psychiatric illnesses as well as their exacerbation.12 When mice are exposed to nocturnal dim light as infants, they grow up to have more anxiety as adults.13 Human studies have found a strong link between rapid flux of spring sunlight and earlier onset of bipolar disorder.14
A study from Japan illustrates the problem for our patients.15 They followed 863 older adults for several years, carefully measuring how much light they were exposed to in their bedrooms. On follow up, the risk of depression was directly correlated with how much light they were exposed to in their bedrooms. Those who slept in pitch darkness had the lowest risk, but what is interesting is how little light was necessary to accomplish the shift: 5 lux – which is equivalent to a night light – was the cut off. Those who slept with at least 5 lux in their bedroom had double the risk of depression 2 years later.
That study was not controlled, although they attempted to control for confounders that might otherwise explain the association. But buried in the discussion was a sentence that struck me. The authors believed that the health risks of evening light are so well documented in animal and epidemiologic human studies that a controlled trial would be unethical in humans. In other words, we already know too much to learn anymore.15
Instead, it is time for action, to educate our patients to follow the natural flow of day and night. That means bright light in the morning, low levels of blue light in the evening, and pitch dark in the bedroom. Those steps are not easy to follow in the modern world, and in a future podcast we will review new technologies that can ease those changes.
KELLIE NEWSOME: Join us then on PsychPearls, and you can also catch us every Monday on the Carlat Psychiatry Podcast.
Chris Aiken, MD, is the Mood Disorders Section Editor for Psychiatric TimesTM, the Editor in Chief of The Carlat Psychiatry Report, and the director of the Mood Treatment Center. He has written several books on mood disorders, most recently The Depression and Bipolar Workbook. He can be heard in the weekly Carlat Psychiatry Podcast with his cohost Kellie Newsome, PMH-NP. The author does not accept honoraria from pharmaceutical companies but receives royalties from PESI for The Depression and Bipolar Workbook and from W.W. Norton & Co. for Bipolar, Not So Much. Kellie L. Newsome, PMH-NP, is the cohost of the Carlat Psychiatry Podcast and is also a practicing psychiatric mental health nurse practitioner in Winston Salem, NC, at the Mood Treatment Center. Raised in Tasmania, Australia, Kellie moved to the United States in 1998.
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