A recent study suggests that the conventional wisdom regarding how the body’s “internal clock,” or circadian rhythm, works may need to be reconsidered. The findings could eventually have a major impact on how doctors address problems such as sleep disorders.
The study, published in the April 29, 2018, issue of The Journal of Physiology, could eventually affect the use of light therapy – a method in which bright lights are used to help people suffering from issues with sleep quality.
Researchers wanted to look into the link between a process known as circadian phase resetting and the suppression of the hormone melatonin. Circadian phase resetting helps the body synchronize to external time cues, such as whether it’s day or night. It’s important that circadian rhythms work properly, because that impacts many cellular and molecular functions. If the body’s clock is not precise, that could lead to trouble sleeping.
Melatonin helps regulate the body clock. The brain produces the hormone during the night. If the supply of melatonin is suppressed because the brain doesn’t produce enough, sleep quality could suffer.
It has long been believed that melatonin production and circadian phase resetting are closely linked. The suppression of melatonin is associated with disruptions in the circadian phase resetting process. Measuring the amount of melatonin, according to conventional medical thinking, provides an accurate picture of how well the body’s circadian phase resetting process is functioning.
But the study casts significant doubt as to whether that link always exists.
Melatonin production and circadian phase resetting may actually operate independently.
A group of 16 adults participated in the inpatient study, which took place at the Brigham and Women’s Hospital in Boston.
Participants stayed in a room where there were no “time cues” whatsoever. They had no access to clocks, live television, radio, the internet, newspapers, or phones. In addition, the rooms in which they stayed had no windows.
Researchers then exposed the participants to varying degrees of exposure to pulses of bright light over a period of nine or 10 days. Some people were exposed continually through the night, while others were exposed sporadically.
The results showed that the different types of light pulses produced equal amounts of melatonin suppression. However, the amount of circadian phase resetting experienced by the participants was not the same. This suggests that melatonin levels alone are not a definitive indicator of the amount of circadian phase resetting that is taking place.
Shedding New Light on Light Therapy
It is possible that the results of the study could change the way doctors use light therapy. Exposure to bright light helps “reset” the internal body clock, allowing for improved sleep patterns. Light therapy is different from nighttime exposure to blue light emitted from tablets, computers, and phones, which may have a negative effect on sleep quality.
Although the results of the study are significant, it is important to note that the conclusions may be limited due to the small sample size of the participants. More work will be needed to determine the impact of these findings on light therapy research.
“Overall our data suggest that melatonin suppression and phase resetting are sometimes correlated, but ultimately are regulated by separate neurophysiological processes,” said Dr. Shadab Rahman, the lead author of the study. “Therefore, melatonin suppression is not a reliable surrogate for phase resetting. This is an important consideration for developing light-therapy treatments for people who have poor quality sleep and biological clock disruption.”
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