Setting the Body Clock in the Dark
"This is an important study, which confirms and extends previous research by both U.S. and European authors," Derk-Jan Dijk, PhD, tells WebMD. "It illustrates the importance of the biological clock in sleep-wake regulation, and shows that 'treating' the clock can 'treat' some sleep disorders." Dijk, who is a chronobiologist at the University of Surrey in Guildford, England, was not involved in the study.
Normally, our body clock is set for a cycle slightly longer than 24 hours, which is why we tend to sleep later each morning, then go to bed later each night if we have time off and don't set the alarm. But the 24-hour cycle of daylight and darkness tends to get us back on track.
"People must be able to perceive light through their eyes in order to synchronize their body clocks to the 24-hour day," researcher Alfred J. Lewy, MD, PhD, tells WebMD. "Blind people drift later each day. When their clocks are reversed, telling them to sleep during the day and stay up at night, they have insomnia and daytime sleepiness," says Lewy, director of the Sleep and Mood Disorders Laboratory at Oregon Health Sciences University in Portland.
"Blind people are under constant jet lag," Sato Honma, MD, PhD, tells WebMD. He's an associate professor of medicine at Hokkaido University in Sapporo, Japan, and was not involved in the study.
In Lewy's study, seven totally blind subjects with sleep disturbances were given either melatonin or a sugar pill one hour before their preferred bedtime for several weeks. After their sleep patterns were recorded, each patient was switched over to the other treatment. Neither the patients nor the nurses knew which medication was being given.
Before treatment and while taking the sugar pill, all seven subjects had sleep problems related to an abnormal daily cycle. Most of them had a cycle longer than 24 hours, and on average, they were about half an hour off. While taking melatonin, six subjects slept better, and their wake-sleep cycle normalized to 24 hours. Three of them continued taking melatonin for three months and continued to sleep well even though the dose was gradually reduced.
"Even on small doses of melatonin, the sleep pattern remained normal," James E. Jan, MD, tells WebMD. "This study has great clinical importance for those unfortunate blind individuals who suffer from this severe, chronic sleep disorder throughout their lives," says Jan, director of the visually impaired program at the British Columbia's Children's Hospital in Vancouver, British Columbia. He was not involved in the study.