Adjusting the Circadian Clock

In the Shetland Islands north of Scotland, just 6∞ south of the Arctic Circle, daylight hours are few in wintertime. Yet the moon is quite bright. Since prehistoric times, natives have passed down the belief that a person sleeping should not be exposed to the bright moonlight. A bath of ill-timed moonlight, the folklore went, would make the person groggy and not well the next day.

The Shetland Islanders of times past were experiencing one manifestation of a now well-established fact of lifeñlight or darkness at unusual times can affect how we feel. Perhaps no one knows that better than a shift-worker, someone whose workday is not a steady 8:00 a.m. to 5:00 p.m.

Night-shift workers chronically fight their circadian, or 24-hour clockñand seldom win. "They try to work at night, when the drive for sleep is at its peak, and they try to sleep during the day, when the waking signal is strongest," says Dr. Charles Czeisler, whose pioneering work on resetting that biological clock led to technology to help shift-workers. Such disturbed sleep cycles increase the risk of gastrointestinal disorders, cardiovascular disease, menstrual irregularities, sleep disordersñand just feeling out of sorts.

In the United States, some 20 million people, or one in five workers, follows an off-kilter schedule. For most of them, the night shift is only a sometimes event. "Shifts always change. Most work schedules have people rotate shifts, because no one wants to always work nights," says Dr. Theodore Baker, president of ShiftWork Systems Inc. in Cambridge, Mass. "Even when people work a fixed night shift, their cycle of light exposure isnít steady. On their days off, they go back to a normal schedule, being active during the day."

The privately-owned ShiftWork Systems was formed in 1993, licensing several patents awarded to Czeisler, Richard Kronauer and James Allan of Brigham and Womenís Hospital, part of Harvard Medical School in Boston. "Their work revolutionized peoplesí thinking of how light could be used in the workplace to help people adjust. For 25 years it had been assumed that humans were relatively insensitive to change in the light pattern of daytime in terms of circadian mechanisms," Baker says.

It isnít coincidence that among shift-workers accidents are more likely to occur in the early morning hours. Truck and train drivers are 15 times more likely to get into an accident during darkness. "Shiftworkers donít adjust, they just keep living with their internal clocks set to be awake during the day and asleep at night. The list is replete with horror stories of people asleep at work and in industrial accidents. These are not just chance, they are statistically significant," says Baker. The explosions at the Three Mile Island and Chernobyl nuclear reactors, and the grounding of the Exxon Valdez oil tanker, all occurred in the early morning hours. Many speculate that worker fatigue played a role in these disasters.

ShiftWork Systems offers employers lighting systems to help shiftworkers align their biological clocks with their work schedules. The product, called Circadian Lighting Systems, has three components: software to continually determine the precise schedule of lighting, a computerized light controller to store and implement the schedules, and high intensity lighting hardware, which resembles large skylights. Fluorescent lamps with a broad range of wavelengths in the visible range provide the illumination. The precise and always-changing pattern of light exposure is coupled with considerations of what is comfortable, as well as how best to conserve energy, Baker says.

Tests to confirm that the Circadian Lighting System exerts a measurable biological effect are very convincing. One type of evidence is the blood and urine levels of melatonin. This much-hyped hormone is normally secreted from the pineal gland in the brain at night but ceases to be made in the morning, as light rays impinge on retinal photoreceptor cells with the arrival of dawn. Thus, melatonin level cycles with the sun, setting a pace that controls many of the bodyís other circadian cycles.

Researchers measured melatonin levels in space-shuttle astronauts and in certain industrial workers using lighting systems. "We showed that the melatonin-secretion rhythm changed rapidly. Instead of being secreted at night, hormone secretion was suppressed at night. Natural melatonin secretion shifted to daytime, when the workers were trying to sleep better," says Baker. "This is a more natural way to promote sleep. Itís better than sleeping pills, which give another 20 minutes of unnatural sleep." It may also be safer than self-medicating with melatonin, which can be purchased at health food stores.

Tests of cognitive function, such as reaction time and grammar usage, also indicated improved performance on the job following use of the Circadian Lighting Systems. In addition, workers kept logs recording when they slept, rested and were awake and alert, and some participants wore wrist computers to verify the information.

Results appeared in short order. "We have very good records of sleeppattern changes. Usually by the second day, sleep increased by an hour. By the end of the week, sleep increased by two to three hours. Thereís a two-fold benefit: The treatment fine-tunes the central nervous system to perform better on the night shift, and the shift in rhythm gives a better dayís sleep," reports Baker.

NASA uses Circadian Lighting Systems to prepare astronauts for night launches and for performing tasks in the darkness of space. A Delaware oil refinery and San Diego Gas and Electric Company use the system to improve the performance and health of its shift-workers.

At the September "Safety of Operating Reactors" meeting held in Seattle, Baker reported on the success of a Circadian Lighting System in use to adjust the asleep and awake cycles of operations officers at Nuclear Regulatory Commission (NRC) facilities in Bethesda and Rockville, Md. These workers are responsible for monitoring and reporting unusual events occurring at nuclear reactors. When switched to the night shift, these officers report difficulty sleeping during the day, inability to remain alert when on the job and commuting, and other problems in their day-to-day lives.

Researchers evaluated the workers four months before and four months after starting to use the lighting system. The workers reported safer commutes, less fatigue on the job, more restful and longer sleep during the day, faster adjustment when their shifts switched, and perhaps most important for public safety, greater confidence in their ability to assess incoming reports.

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