Dr Aiken is Instructor in Clinical Psychiatry at the Wake Forest University School of Medicine and the Director of the Mood Treatment Center in Winston-Salem, NC. He is Editor in Chief of The Carlat Psychiatry Report and a frequent contributor to Psychiatric Times.
The biological clock is set by daily cycles of light and darkness, and regulation of these cycles is a promising avenue of prevention in bipolar disorder. That is exactly what we’re not doing. Smartphones, LED screens, and energy-efficient bulbs emit a blue haze of light that’s shorter in wavelength than the yellowish hue of starlight and candlelight that humans evolved under. This change has potent effects on circadian rhythms.
Blue light and melatonin
Light suppresses melatonin, but not just any light. The color is what matters here, and blue light in the 460 nm to 480 nm range is particularly good at shutting down melatonin and keeping people awake and alert. Rods and cones detect the full spectrum of light for the visual cortex, and a third photoreceptor was discovered in the 1990’s that only responds to blue light. Called melanopsin, it regulates melatonin production by direct communication with the suprachiasmatic nucleus, the time-keeper of the biological clock.1
This means that strong shifts in blue-spectrum light are required to set the biological clock at the two critical 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.2,3
The American Medical Association has released a position statement calling for reductions in nocturnal blue light, which are associated with physical health risks including obesity, diabetes, cancer, cardiovascular and neurologic diseases, gastrointestinal ulcers, and adverse reproductive outcomes.4 These risks are relevant to all people, but particularly to adolescents and people with bipolar disorder, two groups that are particularly sensitive to the biological effects of evening light.5,6
A slightly broken biological clock
Nearly every gear in the biological clock is disrupted in bipolar disorder. Circadian genes are altered and melatonin is delayed, diminished, and more easily suppressed by blue light.5 Shifts in the timing of light and darkness, such as shift work, seasonal changes, and travel across several time zones, can trigger new episodes.7
Dr Aiken does not accept honoraria from pharmaceutical companies but receives royalties from W.W. Norton & Co. for a book he co-authored with James Phelps, MD, Bipolar, Not So Much.
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