SATURDAY, July 31 (HealthDay News) -- When the days grow longer in the spring, teens experience hormonal changes that lead to later bedtimes and associated problems, such as lack of sleep and mood changes, researchers have found.
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In a study of 16 students enrolled in the 8th grade at an upstate New York middle school, researchers collected information on the kids' melatonin levels. Levels of melatonin -- a hormone that tells the body when it's nighttime -- normally start rising two to three hours before a person falls asleep.
The study authors found that melatonin levels in the teens began to rise an average of 20 minutes later in the spring than in the winter. The teens also reported an average 16-minute delay in sleep onset and an average 15-minute reduction in sleep duration in spring compared to winter.
"This is a double-barreled problem for teenagers and their parents," study author Mariana Figueiro, an associate professor at the Lighting Research Center at Rensselaer Polytechnic Institute in Troy, N.Y., said in a news release from the institute.
"In addition to the exposure to more evening daylight, many teens also contend with not getting enough morning light to stimulate the body's biological system, also delaying teens' bedtimes," she explained.
This delay in getting to sleep may lead to sleep deprivation and mood changes, and may also increase the risk of obesity and possibly lower school grades, Figueiro noted.
The study is published in the July issue of the journal Chronobiology International.
"This latest study supplements previous work and supports the general hypothesis that the entire 24-hour pattern of light/dark exposure influences synchronization of the body's circadian clock with the solar day and thus influences teenagers' sleep/wake cycles," Figueiro stated in the news release.
"As a general rule, teenagers should increase morning daylight exposure year round and decrease evening daylight exposure in the spring to help ensure they will get sufficient sleep before going to school," she advised.
-- Robert Preidt
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SOURCE: Rensselaer Polytechnic Institute, news release, July 26, 2010