Too much or too little light can effect health and mood

Jan 26, 2024, 10:16 AM by Dr. Sally Robinson

The Importance of Sleep

Galveston Island is 2024 miles from the equator. Galveston's longest day is 14.9 hours and the shortest is 11.1 hours, a change of 3.8 hours. As you move closer to the north or south poles the difference between the longest and shortest days grows.  The sudden change of one hour with daylight saving time is disruptive for most humans.

Why is this one-hour change bothersome?  Humans, along with other life forms, have evolved complicated, synchronized biological processes which include the sleep-wake cycle, behavior, hormone secretion, cellular function, and gene expression.  Changes in light or dark disrupt these basic biological processes and are now known to be associated with an increasing incidence of certain cancers, metabolism, and mood disorders.

A little over a century ago electric lights became commonplace and with the increased ability to see at night, we now have shift workers (more likely to suffer depression) and increased light pollution. An article by T.A. Bedrosian and R.J. Nelson in Translational Psychiatry says nighttime light can directly affect mood.  One survey found that over a third of parents and children leave an electronic device on while sleeping.  This amount of nighttime light exposure is unprecedented in human history. Too much light at night is implicated in mood disorders including disruption of sleep. 

Childhood and adolescence are periods of time with an increased likelihood of nighttime light exposure.  Children commonly sleep with night lights and adolescents tend to stay up late using electronics.  Compounding the tendency to stay up later, young people tend to be more sensitive to the melatonin-suppressing effects of light at night than adults.  Turning off devices to sleep helps.

It would seem that if too much light is causing mood changes then we should have complete darkness at least for sleep. But other problem occurs with increased darkness. In Alaska’s most northern town they have “30 days of night” and more Seasonal Affective Disorder (SAD).  This is a type of depression that follows a seasonal pattern most commonly in the winter with its long nights.  Researchers have not determined what causes SAD but evidence points to a disruption of the body’s natural cycle of sleeping and waking. Who would have thought it?  Sunlight plays a role in the brain’s productions of melatonin and serotonin.  During winter the body produces more melatonin (which encourages sleep) and less serotonin (which fights depression).

SAD is more often recognized in adolescents and adults primarily as it takes time to see if there is a pattern.  For diagnosis a pattern should be present for at least 2 years.

The key word with problems of light and darkness is disruption.  The evidence suggest that circadian disruption alters the function of the brain regions involved in emotion and mood regulation.  Treatment of SAD is exposure to more daylight with open windows, just being outside or “light therapy” using a light box or UV filtered light visors.

Either a lack or an excess of light can have significant effects on health and mood. 

Sally Robinson, MD  Clinical Professor
UTMB Pediatrics - Children's Complex Care
Also see:  Pediatric Primary Care

Published 01/24

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