Body's clock keeps insomniacs wide awake.

Body's clock keeps insomniacs wide awake

Scientists have postulated that people who have trouble falling asleep at night may have an out-of-kilter biological clock, the circadian rhythm regulating alertness, sleepiness and many other bodily cycles. Australian researchers now offer hard data supporting that hypothesis.

Mary Morris, Leon Lack and their colleagues at Flinders University in Adelaide studied 13 sleep-onset insomniacs -- people who go to bed and can't sleep for at least 42 minutes. They compared the insomniacs, ranging from 20 to 45 years of age, with nine good sleepers who typically fell asleep within 11 minutes. All study participants kept sleep diaries for two weeks, then checked into a sleep laboratory for several days. There Morris and her colleagues monitored participants' endogenous body temperature -- a gauge unaffected by activity-related temperature fluctuations and used as a marker of the body's biological clock.

The researchers found that the 13 insomniacs passed through the wake-maintenance zone -- a stage in the biological cycle during which sleeping is difficult -- about 3.6 hours later than controls. Most people leave the wake-maintenance zone at about 10 p.m., but insomniacs in the study reached the same point in their cycle after 1 a.m., Lack says.

Most sleep-onset insomniacs are people aged 15 to 50 who are desperately seeking a good night's sleep, Lack says. Many go to bed at midnight but toss and turn for hours. The new research suggests their trouble may be related to a delay in the circadian cycle, and offers hope that using bright lights to reset the biological clock -- a strategy currently under study (SN: 6/17/89, p.374) -- will offer some relief.