Exposure to bright light and darkness to treat physiologic maladaptation to night work

Working at night can cause disturbances in the sleep-wake cycle that lead to insomnia during the day and reduced alertness with fatigue while on the job at night. There are also medical consequences; people who rotate shifts over the long term have an elevated risk of developing heart disease, digestive problems, and in women, reproductive dysfunction. Even people who remain on a permanent night-shift for many years do not fully adjust. Researchers have discovered that the hypothalamus, a region of the brain, is responsible for regulating the body's circadian (24-hour) rhythms. For this reason, the hypothalamus has been called the pacemaker of the circadian rhythms. It was once thought that the hypothalamus 'set' the daily rhythms according to the timing of social interaction, but the authors have recently demonstrated that it responds instead to darkness and light, and can actually be 'reset' by up to 12 hours over a period of two to three days. In this study, eight young men were exposed to bright light at night and almost total darkness during the day in an attempt to improve their adjustment to night work. Circadian adaptation was measured by monitoring body temperature, which is normally at its lowest in the middle of the night; if the subjects were to adapt to night work it would shift to reach a 24-hour low during the day. This adaptation was in fact achieved. The low temperature occurred in the midafternoon after four days of the treatment, which consisted of exposure to bright lighting at night and darkness while sleeping during the day. Other physiologic signs confirmed the conclusions based on body temperature. The subjects also reported improved alertness and mental functioning at night. Therefore, manipulation of lighting conditions can correct the maladaptation of the human circadian rhythms to night work. (Consumer Summary produced by Reliance Medical Information, Inc.)