Effects of moderately bright light on subjective evaluations in healthy elderly women

INTRODUCTION

Morning bright light therapy has been reported to be effective for sleep and behavioral disorders in elderly patients with dementia.¹ It has also been reported that in healthy elderly men, a short duration of morning bright light had an effect on sleep maintenance without changing their daytime activity.²

As proposed by Terman,⁴ ophthalmological disturbances should be considered when performing bright light treatment, especially with the elderly. Lower intensity light is preferable to the elderly. The purpose of this study was to investigate the direct effects of moderately bright light (1000 lux) on subjective feelings in elderly women. Moreover, we investigated body temperature rhythm to ascertain whether these changes in subjective feelings were related to circadian rhythm.

METHODS

This experiment was carried out from late August to early December of 1997 in Sapporo. Eight healthy women (mean age: 67.4 years, range 56–79 years) participated in this study after giving informed consent. Subjects who were on medication, or who were mentally or physically ill were excluded. They maintained a regular sleep–wake schedule throughout the experimental period. The subjects were examined under moderately bright light (BL) condition and controlled (CL) condition in their homes. Light exposure was provided for 1 h in the morning. Light intensity was set at about 1000 lux at eye level. The subjects sat in front of a lighting device (a flat panel tray type). They were instructed to read materials printed on OHP film and also to play games on the lighting device. Consequently the subjects were looking directly at the light source for 1 h. As a controlled condition, they sat in front of the device without light exposure. The experiments were performed in a counterbalanced crossover design with an interval of 1 week.

To assess the effect of light exposure, subjective feelings for alertness, mood, motivation, happiness, refreshment, concentration and appetite were evaluated using a Visual Analog Scale (VAS) morning and night. Subjective sleep feelings using the OSA inventory consisted of five categories: F1 (sleepiness); F2 (sleep maintenance); F3 (anxiety); F4 (integrated sleep); F5 (sleep initiation). These reports were obtained successively in the morning for 6 days. We measured motor activity with a wrist actigraph (Ambulatory Monitoring Inc.), worn on the non-dominant hand. Motor activity per 5 min was recorded during the six successive days and we analyzed the nocturnal data (bedtime to wake-up time). Rectal temperature was also monitored simultaneously every 5 min. Mesor, amplitude and acrophase were determined by using the cosinor method. We used the Wilcoxon signed rank test for statistical analysis.

RESULTS

Figure 1 represents morning VAS scores across 7 days from the baseline to the sixth day of light exposure. In comparison to the CL condition, subjects reported significantly increased alertness, mood, motivation, happiness, refreshment, concentration and appetite after the second BL exposure (P < 0.05). Moreover, the pre-exposure day for subjective sleep feelings was set at a 100% baseline (Fig. 2). The scores of sleep maintenance, anxiety and integrated sleep feeling significantly increased on the fourth day of BL exposure (P < 0.02, P < 0.02 and P < 0.05, respectively), suggesting that sleep quality improved in the BL condition.

The average count of motor activity during sleep was unchanged in the two conditions. There were no significant differences in the acrophase, mesor and amplitude of rectal temperature rhythm between the BL and CL conditions.

DISCUSSION

Effects of moderately bright light exposure on subjective feelings were immediately apparent after two or four exposures to light, although a fluctuation was noted. Maintaining the stability for subjective feelings may require further intensity, duration and number of consecutive light exposures.

Light of approximately 1260 lux produced phase advances of temperature rhythm.⁵ In our study moderately bright light exposure (1000 lux) improved subjective sleep feelings and enhanced subjective alertness in elderly women without changing the phase of rectal temperature rhythm. These findings suggest that light of low intensity has immediate effects on human physiology or psychology, independent of the circadian phase.

Some reports^6,7 have supported our findings and they have shown that single nocturnal bright light exposure (1000 lux) enhanced self-reported alertness or objective EEG analysis during the night in healthy young subjects. However, Genhart et al.⁸ reported that the sleep of normal elderly women with no seasonal variations in mood and behavior was not influenced by bright light treatment. Moreover, bright light exposure made these women feel more irritable, anxious and agitated. These differences may be due to the intensity or duration of light. In their study, high intensity light (2500 lux) and longer durations of light treatment (from 07.00 to 09.30 h and 19.00 to 21.30 h) were administered to elderly women.