[This speaks well for night lights in hallways and keeping lights off when getting
up for meds and night trips to bathroom]
Middle of the Night Wakening Throws Off Body Clock
Thu Apr 18, 2002 By Anne Harding
NEW YORK (Reuters Health) - Being woken up and exposed to bright light at night can
throw off a person's biological clock for the next few days, a new study shows.
What's more, the researchers found that being woken up at night at all--even in a
dark room--also disrupts the body's timing, although to a lesser degree.
The wakening seem to introduce a "lag" into the body clock, pushing back the release
of hormones and other body processes by as much as an hour and a half.
While such sleep interruptions don't harm health, a person experiencing such a delay
in the body clock "would feel tired in the morning and feel more aroused in the
early evening," said study author Samir Bangalore, a student research fellow in the
Sleep and Circadian Rhythms Research Laboratory of Northwestern University Medical
School in Chicago, Illinois.
The findings also offer clues to treating seasonal depression and other conditions
marked by biological clock abnormalities, the researcher told Reuters Health.
Bangalore presented his findings Thursday at the American Academy of Neurology (news
- web sites)'s annual meeting in Denver, Colorado.
Humans--and many other creatures--have roughly 24-hour body clocks that help
regulate sleep patterns and energy levels, and also govern when hormones are
secreted and other biological processes occur. These daily patterns are called
circadian rhythms.
Bangalore and his colleagues tested the effects of awakening and nighttime bright
light exposure on the circadian rhythms of 32 healthy volunteers. The study
participants spent one night sleeping in the dark for 8 hours at the time that was
normal for them. The next night, some patients were woken up and exposed to 1, 2 or
3 hours of bright light. As a "control," some patients were kept awake for varying
amounts of time but not exposed to light.
Bangalore and his colleagues gauged the state of participants' biological clocks by
measuring their secretion of melatonin. Release of this hormone, which peaks at
night, is partially regulated by the biological clock.
"Light pulses of 1, 2, or 3 hours all led to significant delays in the circadian
rhythm of the melatonin profile by 35 to 75 minutes," Bangalore said. Patients who
were kept awake for 4 hours but not exposed to light also had a half-hour delay in
melatonin secretion, while small delays were also seen in people who were kept awake
in the dark for shorter amounts of time.
Such delays would persist for a few days, he noted. For example, a person would feel
the effects of an hour's delay in melatonin secretion for 3 or 4 days.
Bangalore points out that the findings help "clarify the relationship between the
duration of light exposure and the response of the biological clock."
This is important, he notes, because circadian rhythm disorders have been linked to
many health problems. For example, elderly people often have advanced biological
rhythms, meaning they fall asleep and wake up early, while adolescents have delayed
ones. Both states can lead to severe sleep deprivation.
People suffering from seasonal affective disorder (SAD) often have disordered
circadian rhythms, and some researchers believe light exposure helps SAD patients
because it normalizes these rhythms.
http://story.news.yahoo.com/news?tmpl=story&u=/nm/20020418/hl_nm/sleep_timing_1
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