Illumination levels in nursing home patients: effects on sleep and activity rhythms

Studies examining levels of illumination in adult populations have demonstr ated that the level and amount of light exposure are lower in the elderly c ompared with younger adults, particularly in institutionalized patients wit h dementia. Although insufficient light exposure has been implied as a caus e of sleep fragmentation, evidence for such a relationship is scant. Sixty- six institutionalized elderly had their activity and light exposure monitor ed for a 3-day period. Mean and median light levels, minutes spent over 100 0 and over 2000 lux, percent sleep and wake, and number of naps were comput ed for daytime intervals, defined as 07.00 18.59. Percentages of sleep and wake, number of awakenings and mean duration of wake periods were computed for night-time intervals, defined as 22.00 05.59. Mesor, amplitude and acro phase of activity and of light were determined by cosinor analysis. A mixed linear model was used to assess the effects of daytime Actillume measures on subsequent night-time measures, and vice verse. Spearman correlations we re computed, and multiple regression analyses were carried out with light v ariables and dementia level as predictors and sleep-wake and activity measu res as dependent variables. The median light level was 54 lux and a median of only 10.5 min were spent over 1000 lux. Higher light levels predicted fe wer night-time awakenings, and severe dementia predicted more daytime sleep and lower mean activity. Increased bright light exposure predicted later a ctivity acrophase. There was an association between the acrophases of light and of activity, with maximum illumination preceding peak activity. These results suggest that daytime light exposure has an impact on both night-tim e sleep consolidation and timing of peak activity level.