Increased light exposure, whether in the morning or evening, did not improve measures of nighttime sleep or daytime alertness. However, results suggested that morning bright light might delay circadian rhythms and improve circadian rhythm quality in nursing home residents.
It is not clear why light treatment in our study produced results different from those of other investigators, but there are several possible explanations. First, the level of dementia in the current study may have been more severe than those in some other studies. Our patients were severely demented, with a mean MMSE score of 12.8 (median = 9). Other studies that examined the effect of light treatment in dementia used moderately and severely demented patients, but did not report the precise level of impairment. In addition, no distinction was made between patients with AD and those with other types of dementia in the current study. It is possible that light treatment might improve sleep in some types of dementia but not others. We are currently replicating this study in a more homogenous group of patients with possible or probable AD.
In other studies of light treatment, subjective ratings often resulted in improvements, whereas objective ratings, all based on wrist activity, showed improvements in both inter and intra-daily variability but did not consistently show improvements in percentage of time asleep or awake. In one of the first studies of the effect of light on sleep in AD, Okawa et al. conducted a series of studies in which patients were exposed to anywhere from 3,000 to 8,000 lux in the morning from 9:00 a.m. to 11:00 p.m.24,26–28,32
Two of the studies used nurses’ ratings of sleep and resulted in half the patients showing an improvement in ratings in the first study26
and a significant improvement in ratings of sleep in the second study.28
Two other studies also used staff ratings of sleep. Lyketsos et al.,33
administered 2,500 lux of light to eight demented and agitated nursing home patients in the morning for 4 weeks. Nursing staff completed sleep logs that indicated that nighttime sleep improved significantly in these patients compared with 4 weeks with dim light exposure. Koyama et al.,29
studied six nursing home patients with dementia with 4,000 lux administered from 9:30 a.m. to 11:30 p.m. for half the subjects and from 11:00 a.m. to noon for the other three subjects. Nursing staff observations and sleep log records indicated that three of six subjects had significant improvements in rated percentage of nighttime sleep and two of six had significant improvements in rated percentage of daytime wakefulness.
In a more recent study by Okawa et al. using wrist actigraphs, only patients with vascular dementia showed a decrease in nighttime activity after light treatment. There were no improvements in the patients with AD.32
Satlin et al.25
exposed patients with AD to evening bright light, and, in 80% of the patients studied, staff's ratings of sleep/wake improved; moreover, based on wrist activity, there was a significant decrease in intradaily variability, percentage of nocturnal activity, and severity of sundowning behavior and a significant increase in the amplitude of the rhythm.
A second study also found changes in variability/stability. Van Someren et al.30
exposed 22 demented patients to all-day indirect bright light with an mean of 1,136 lux. After 4 weeks of treatment, wrist activity data indicated a significant increase in interdaily stability (suggesting an increase in the strength of the coupling between the rhythm and environmental cues) and decreased intradaily variability (indicating less fragmentation).
One additional study examined the effect of light on AD patients living in the community. Five patients were exposed to 2 hours of morning light at 2,000 lux between 7:00 a.m. and 9:30 a.m. using light visors for 10 days. This study found no significant changes in any sleep or rhythm parameters.31
The only previous study to administer evening bright light was Satlin et al.,25
in which light treatment was administered from 7:00 p.m. to 9:00 p.m., with a resulting improvement in sleep. When this protocol was initially planned, evening bright light was also to be administered from 7:00 p.m. to 9:00 p.m., and afternoon light was to be administered between 2:00 p.m. and 4:00 p.m., a time expected to have no “phase shifting” effects on circadian rhythms. However, when the protocol commenced, it became clear that this group of nursing home patients went to bed by 7:30 p.m., and treatment time was therefore shifted to occur immediately before bedtime, between 5:30 p.m. and 7:30 p.m. This forced original afternoon treatment time to be moved to the morning before lunch, between 9:30 a.m. and 11:30 a.m. These untraditional times may account for some of the discrepancies in results.
To determine whether sleep improves at night, one needs a reliable definition of “night,” (i.e., a measure of bedtime and uptime). Other studies have not reported how they defined night and day. In this study, because the patients were sleeping on and off throughout the day and night, it was not possible to tell when they actually went to bed; therefore, times had to be chosen to define night. It is possible that, had we known the true bedtimes, the data may have appeared somewhat different. We are currently replicating this protocol with observed bedtimes and uptimes.
The current study included two “control” groups, one as a control for staff interaction during light (DSR) and one as a control for the light itself (dim red light). Only two other studies had control conditions, one of which only used observations33
and the other which found no results in AD patients.32
Therefore, in all the other studies, it may not have been the light alone that accounted for the findings.
Our patients were fairly compliant, but, even with staff accompanying them during treatment, the average duration of light therapy was only 92 minutes. It is not easy to encourage demented older people to stay awake and to sit continuously for 2 hours in front of a light box. Having the light on for 2 hours is no guarantee that the patients are awake and actually sitting in front of the light for the full time. Although other studies reported the duration of light therapy sessions (the length of time the light was on), no other study reported patient compliance with treatment. It is therefore unknown whether patients in these other studies received less or more light exposure than our sample.
The compliance issue raises another important point. As mentioned, it was difficult to keep patients sitting in front of light boxes. Even with constant companionship, patients still had a tendency to wander away or fall asleep. In the clinical setting, staff would rarely have the time to sit with patients during treatment. Van Someren et al.30
had ceiling-mounted high-intensity lights placed in the living rooms of the nursing homes. Colenda et al.31
had patients wear bright light visors rather than using bright light boxes. Although the patients tolerated the visors, the intervention resulted in no significant improvements in measures of sleep or circadian rhythms. In facilities that wish to shift patients’ activity rhythms with the use of bright light, the most clinically relevant recommendation would be to install bright lights in the ceiling with controls that would allow them to be regulated for lux level, timing, and duration.
Another unexpected finding was that morning bright light delayed circadian activity rhythms in this study. It is important to note that the acrophase was delayed in every patient in this treatment group. This was not simply the result of aggregating data across subjects. In younger adults, morning light generally advances circadian rhythms,23
but the phase delay seen here suggests that the rhythms of demented older individuals may be different. Light exposure of the same intensity, at different times of the day, results in different phase shifts. This is called the phase response curve (PRC).48
The PRC is linked to the time that intrinsic melatonin secretion begins (dim light melatonin onset (DLMO)). In normal adults, DLMO typically occurs at 9:00 p.m. Based on Lewy's theory of the PRC to light,48
bright light exposure between 1:00 p.m. and 9:00 p.m. will delay the circadian rhythm. This occurs 8 hours before the DLMO and is called the delay portion of the PRC. The advance portion of the PRC falls before 1:00 p.m. (see , Panel A). Because older people are phase advanced relative to younger adults,6–9
DLMO would also be phase advanced. Lewy's theory would suggest that DLMO in these older people who are phase advanced occurs at perhaps 5:30 p.m. rather than at 9:00 p.m., which would place the delay portion of the PRC between approximately 9:30 a.m. and 5:30 p.m. (, Panel B). This was the time of the morning light treatment. Therefore, if these older people are phase advanced, the phase delay zone of the light PRC may have been stimulated with the morning bright light, thus resulting in a change in circadian rhythms opposite of what would be expected in young adults. There may also be other theories to explain this finding. Additional research still needs to be done.
Figure 4 Dim light melatonin onset (DLMO) and phase response curve in normal older people (a) and older people who are phase advanced (b). In normal middle-aged adults, DLMO is at approximately 9:00 p.m., 2 hours before bedtime. The delay portion of the phase (more ...)
In summary, although none of the treatments explored improved sleep at night or alertness during the day in these older, primarily demented individuals, increasing exposure to morning bright light delayed the acrophase of the activity rhythm and made the circadian rhythm more robust. These changes have the potential to be clinically beneficial, because it may be easier to provide nursing care to patients who have more socially acceptable circadian activity patterns. Morning bright light has also been shown to improve agitated behavior in a small subsample of this same group of subjects.49
The results of this study are consistent with the viewpoint that light treatment in the nursing home is difficult to apply and results are not robust. This is different from studies of bright light treatment of depression,50
or delayed sleep phase,51
where there are large, robust improvements with groups consisting of as few as 10 subjects. Although the sample size in the current study was relatively large for a light therapy trial, it is rather small for standard treatment trials. For example, studies of treatment of depression with antidepressant medications are no more robust than the current study and require 40 to 50 subjects in each group, treated for 8 to 16 weeks, to find a significant treatment effect.52
The possibility that treatment effects exist in this study should not be discounted; rather, additional larger trials are still needed to determine whether light administered at different times to patients with known AD will have a beneficial effect on sleep.