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Sleeping when it's light? Your circadian rhythm may be off

Sleeping with the light on can make your circadian rhythm miss a beat. Now, medical researchers are beginning to understand why.

A new study published in the Journal of Physiology explores how missing sleep during the dark hours of the night can affect the production of melatonin. The hormone, which helps regulate sleep and is produced by the brain during the night, can be suppressed if someone is frequently exposed to light before sleep.

In a 9- to 10-day inpatient study at Brigham and Women’s Hospital, researchers used continuous and intermittent light during sleeping periods to test whether melatonin suppression and the circadian rhythm are connected. The study included tight control over the participants activity levels and sleep/wake schedule.

The team hopes to find whether a correlation between melatonin levels and circadian phase resetting – the process that sets the internal clock using day and night cues from one’s environment – might equal causation.

But in the end, the research didn’t show a strong link. The intermittent light patterns were shown to trigger larger phase shifts, even though they caused less melatonin suppression.

“Overall, our data suggest that melatonin suppression and phase resetting are sometimes correlated, but ultimately are regulated by separate neurophysiological processes. Therefore melatonin suppression is not a reliable surrogate for phase resetting,” said Dr. Shadab Rahman, who led the study.

The study could have an impact on people who have poor quality sleep, like shift workers, as well as those battling depression.

The small sample size indicates that more research is needed, the researchers warned. Still, it may be time to look into techniques other than melatonin suppression to reset circadian rhythm.

“This is an important consideration for developing light-therapy treatments for people who have poor quality sleep and biological clock disruption, such as shift workers, or disorders such as depression. Additional work is needed to optimize light therapy protocols used as treatment,” Rahman said.

By Kyla Cathey, staff writer

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