The chaos of the lives of those who suffer from Alzheimer's disease extends to their sleep as well. Alzheimer's patients tend to sleep and wake at random times rather than following the orderly sleep cycle of normal people. Such unpredictability disrupts the lives of both patient and caregiver. In a pilot study, researchers at the Lighting Research Center (LRC) of Rensselaer Polytechnic Institute have discovered that the radiation from blue light-emitting diodes (LEDs) can help Alzheimer sufferers to sleep better—a result that could mean relief for millions.
The circadian pattern of sleep in humans is regulated by the cycle of daylight and darkness. The photoreceptors that mediate the circadian system remain undiscovered, but are thought to be something different from the rods and cones of the eye. Whatever these photoreceptors may be, the circadian system has been found to be most sensitive at wavelengths shorter than the yellow-green peak in spectral sensitivity of the retina. For their experiment, the LRC researchers built tabletop light fixtures containing gallium nitride-based LEDs that bathe subjects in blue light (see figure). For a control, the researchers constructed fixtures containing LEDs that emit red light—a spectral band thought not to affect the circadian system.
The six-week study took place at a health-care center for seniors in Clifton Park, NY. The four patients in the study followed their usual routines for most of the day, but were brought into a common room in the evening, where they were exposed to LED light at intensities of approximately 30 lux at the cornea. The first ten evenings' exposure was to red light, followed by ten evenings of blue light; six days followed during which there was no exposure to LED light. Body (eardrum) temperatures were taken and sleep observations made during the last four evenings of the control and test period. The patients with more-advanced Alzheimer's did not remain in front of the light fixture for the whole time, and therefore received an irregular exposure.
Even so, the results showed that the blue light delayed the nightly decline in patients' body temperature by two hours. In addition, the patients slept better between 2 and 4 a.m. after exposure to blue LED light. Two patients fitted with wrist activity monitors became more active during the day and less so at night.
"In general, body temperature is high during the day and low at night, reaching a trough around 4 or 5 a.m.," explains Marian Figueiro, one of the researchers. "Older adults are normally phase advanced, which means that they go to bed early and wake up early. This implies that their body temperature reaches a trough earlier at night than normal adults. Low body temperature is correlated with sleep. However, because we did not measure body temperature over 24 hours, we cannot state that these patients were phase advanced and that delaying the decline of their body temperature was beneficial for their sleep. All we are saying is that the delay in decline of body temperature is consistent with literature showing that applying light in the evening delays the circadian clock." A larger follow-up study is being planned.
