by Helen J. Burgess
Department of Psychiatry, Sleep and Circadian Research Laboratory, University of Michigan, Ann Arbor USA
Helen J. Burgess PhD is Professor in the Department of Psychiatry and Co-Director of the Sleep and Circadian Research Laboratory at the University of Michigan. She has long investigated the chronobiological actions of light in humans, and now studies light in new clinical applications.
Light exposure has profound effects on our mental and physical health. This isn’t surprising considering our physiology evolved in a 24-hour light:dark cycle. Light has many effects: for example, it influences the timing of the circadian clock, alters brain neurotransmitters such as serotonin, suppresses the nocturnal hormone melatonin, and affects sleep. These aspects of physiology are most affected by blue wavelength light.
When thinking of the effects of light on health, it can be useful to consider what is “good” light exposure and what we understand today as “bad” light exposure. Light exposure that can negatively impact health includes artificial evening light after sunset. Evening light can shift our circadian clocks later, suppress melatonin, and disturb sleep, effects that significantly increase the risk for a variety of mental and physical health disorders, from depression to cardiometabolic disease. Unfortunately, evening light has become even more potent in the past years due to the increased use of blue-screen LED devices in the hours before intended sleep. “Good light” for most of us is morning light, and also exposure to more natural light outdoors during the day. This timing of light helps shift our circadian clock earlier, and can even increase brain serotonin levels, which is usually associated with mood improvement. Indeed, morning light therapy is established as an antidepressant in both seasonal and non-seasonal affective disorders.
In our research, we became interested in exploring whether morning light treatment could also assist with clinical disorders beyond depression. Chronic pain is very much influenced by mood and sleep, with improved sleep and mood leading to reduced pain. In our first pilot study we studied people with fibromyalgia, a chronic pain condition. We found that only 6 mornings of 1-hour light treatment led to clinically meaningful improvement in function and pain sensitivity. We are now conducting a larger randomized clinical trial funded by the US National Institutes of Health (NIH) to test 4 weeks of a 1-hour morning light treatment vs placebo in 60 people with fibromyalgia.
The positive results in our fibromyalgia pilot study also led us to funding by a joint NIH-Department of Defense (DOD) initiative to explore non-pharmacological treatments for chronic pain in veterans. We found that 13 days of a 1-hour morning light treatment led to reduced pain and pain sensitivity, improved sleep quality, and, indeed, reduced post-traumatic stress disorder (PTSD) symptoms. We followed up by testing morning light vs placebo in people with significant PTSD symptoms who had experienced a traumatic event, and continued to find reductions in PTSD and depressive symptoms with active treatment. In a new NIH study, using functional magnetic resonance imaging, we are examining different doses of morning light (15 min, 30 min or 1 hour per day for 4 weeks) on the activity of the amygdala, a brain center highly involved in emotional processing.
We know light treatment works, but exactly how remains to be determined. We need to begin thinking of light, alongside sleep, diet and exercise, as essential for our mental and physical health.