B O S T O N, Oct. 11, 2000 -- For the 200,000 Americans who are completely blind, darkness is a constant, but sleep is often disturbed.
Without light cues that the rest of us rely on to synchronize our body clocks, as many as half of these blind people may have difficulty getting sleep schedules in step with a 24-hour cycle and may suffer sleep disorders as a result, researchers say.
But a new study shows that a daily dose of melatonin may be able to help reset a blind person’s unregulated body clock to a daily schedule, making it easier to rise and shine. The research, from a team of doctors at Oregon Health Sciences University in Portland, is in the Oct. 12 issue of the New England Journal of Medicine.
According to Dr. Alfred Lewy, a co-author of the study, this finding can also be applied to those with sight who experience shift changes at jobs, jet lag, daylight-saving time adjustment problems, winter depression and the “Monday Blues.”
Melatonin Revisited Melatonin is a hormone produced every evening by the brain’s pineal gland. Apparently, the chemical helps facilitate the onset of sleep. Darkness serves as a cue for the body to secrete melatonin into the blood stream and light serves to suppress it. Melatonin production also drops with age, possibly causing the elderly to get less sleep.
In recent years, melatonin has been hailed as a “wonder drug,” with proponents claiming it could be used for everything from fighting aging to improving one’s sex drive, without evidence from human studies, Lewy says. Because melatonin is a naturally occurring hormone, companies sell it as an over-the-counter dietary supplement — without any regulation by the Food and Drug Administration or thorough testing of any potential health claims.
“This study cuts through all the hype and spurious claims for melatonin a few years ago, and establishes its main use in humans: to help people with body clock disorders,” Lewy says.
Out of Step Scientists have known for some time that most people’s body clocks are naturally out of sync with the Earth’s 24-hour light and darkness cycle. When human subjects are placed in windowless rooms without any time cues, most people naturally drift into a a sleep-and-wake cycle that is approximately 25 to 26 hours long. Scientists do not know why humans evolved to have a 25-hour cycle rather than a 24-hour one.
A person living in this “natural,” 25-hour windowless world would rotate through the 24-hour sleep cycle every 24 days, and by the 11th day, approximately, would be sleeping only during daytime hours. If such a person were returned to the regular world, he or she would have trouble getting back in step and would be groggy.
People with normal vision can use light, transmitted through the retina to the brain’s internal clock, to reset their internal schedule to the Earth’s 24-hour rotation. Light also allows them to eventually readjust to minor changes in time, such as the switch to or from daylight-saving time or flying from one time zone to a destination in another.
Blind people, however, lack this visual cue, leaving them more susceptible to fall into a 25-hour rhythm that eventually disrupts a daily sleep schedule. Melatonin has been believed to act as a replacement for the light cues.
For those with sight who also need to readjust their body clocks, such as for jet lag or a shift change, using melatonin shortly before sleep may work as well, Lewy says.
Before this study, the proper dosages of melatonin and when to administer them have been unclear, according to Dr. Rafael Pelayo, a psychiatrist at the Stanford University Medical Center.
Capturing the Clock In this research, Lewy and his colleagues gave relatively high doses of 10 milligrams of melatonin to seven blind people an hour before bedtime each day. They found the amount and the timing of the hormone was effective in “capturing” their “free-running” rhythms and allowed six of them to a perfect 24-hour time schedule.
The researchers also progressively reduced the dosages in three of the patients to the amount the body naturally produces — around 0.5 milligrams — for four months. They found the patients were still able to sustain a normal 24-hour rhythm.
“It appears that treatment with a high dose of melatonin may be used to ‘capture’ a free-running rhythm, but that the dose can be gradually reduced,” the researchers wrote.
Lewy explains the blind patients should take this low dose every day for the rest of their lives if they want to remain in a 24-hour cycle.
But Dr. Peter Fotinakes, head of the sleep disorders center at the University of California in Irvine, says that while melatonin use is believed to be safe in the short term, researchers have not established whether it may cause complications in the long term. “Melatonin is best used in conjunction with a sleep specialist,” he warns.