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This article was published 22/9/2010 (3658 days ago), so information in it may no longer be current.
Exposure to natural light is acutely therapeutic to humans. Morning light is especially important because its wavelengths impact enormously on biorhythms.
Rhythmicity is a fundamental theme of human life, and its patterns reflect the cycle of day and night. But an increasingly indoor existence has dramatically reduced exposure to vital outdoor light.
According to extensive research at Rensselaer Polytechnic Institute, lack of exposure to natural outdoor light is messing up human biorhythms, especially in teenagers.
According to Mariana Figueiro of Rensselaer, different light wavelengths impact on different photoreceptors with various effects on associated retinal systems.
Insufficient daily morning light exposure generates decreased alertness, appetite disorders and hormone imbalances, especially in teens, Figueiro says. "Morning-deprived teenagers... underperform on standardized tests" and many experience the so-called "night-owl syndrome," she explained in a recent report.
Inadequate exposure to morning light is linked to early school-day start times and inferior natural lighting in school buildings, researchers have concluded.
"The amount of natural light indoors is below the threshold" to perpetuate the circadian rhythm, according to Figuiero. Sleep disorders can result.
Researcher Mary Carskadon at E.P. Bradley Hospital says inadequate exposure to vital morning light, insufficient infusion of natural light into schools and indoor-oriented activities of modern teens combine to produce below-par academic performances.
"Teenagers build up a huge sleep debt, and sleepy kids don't learn much," Carskadon concluded.
In one 1988 study, 54 per cent of high school students complained they were not getting enough sleep.
A study by Carskadon and Amy Wolfson concluded that because teens do not get enough sleep during the week, at least partly due to melatonin deficits caused by lack of morning light, they sleep late on weekends to "pay back a sleep deficit."
"Earlier school day start time is a major externally imposed constraint on teenagers," the researchers concluded. Weekday under-sleeping in 13 to 19-year-olds can average 89 to 95 minutes. According to studies by Liliane Reis and Frida Fischer at the University of S�£o Paulo, high-school-aged boys sleep less than girls on weekends, and the most common complaint of high school students in their research was "difficulty in waking up" on weekdays.
On average, high school students get 2.5 hours less sleep per night compared with primary school students.
Lack of exposure to morning light causes such sleep disorders as well as irregular bed times, academic difficulties in school, daytime sleepiness, depressed mood and sleep-wake behaviour problems, concluded Christine Acebo at Brown University.
A Hôpital du Sacré-Coeur (Montreal) study showed sleep-pattern disorders are cumulative.
According to researchers Peter Marler and William Hamilton, human biological clocks continue to run after being reset (by such influences as insufficient exposure to morning light), and they continue to run out of phase by the same amount indefinitely.
Carskadon's research shows students with low grades have significantly more sleep disorders compared with students with higher grades.
"The way they sleep actually influences their ability to think, behave and feel during day time hours," she concluded.
Researchers conclude that remedial action includes later school-day start times and proper natural lighting in schools to regulate circadian rhythms properly. In particular, school windows should be designed to "capture" morning light, they recommend.
Robert Alison is a zoologist based in Victoria, B.C.
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