Middle of the night wakening throws off body clock

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Middle of the night wakening throws off body clock

By Anne Harding

NEW YORK, Apr 18 (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'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.