INTRA- AND INTER-INDIVIDUAL VARIABILITY IN SLEEP: ASSOCIATIONS WITH NEGATIVE AFFECT AND SYMPATHO-ADRENAL MEDULLARY ACTIVITY

摘要

The majority of sleep research in adults has emphasized inter-individual, as opposed to intra-individual differences, in dimensions of sleep. The current study quantifies individual variability in actigraphy-measured sleep duration and fragmentation and describes the sociodemographic and psychosocial correlates of such variability in a sample of Black and White adults. It then examines the unique associations of average sleep duration, average sleep fragmentation, and individual variability in these parameters with negative affect and nocturnal sympatho-adrenal medullary activity as indexed by catecholamine levels. The sample included 187 adults (53% men; 41% Black; mean age 59.6 years) who wore a wrist actigraph for nine nights and completed well-validated measures of depressive symptoms, anxiety, and hostility. Overnight urinary catecholamine levels were collected over two 15-hour periods. Estimates of within-individual variability in both sleep duration and fragmentation exceeded between-individual differences, and women and Blacks had more individual variability in sleep duration and fragmentation, respectively. In linear regression models, increased variability in sleep parameters was related to reports of stressful life events and a global measure of sleep quality, independent of average sleep parameters. No associations between sleep parameters and negative affect or catecholamine levels were observed, with the exception of a relationship between increased sleep fragmentation and higher nocturnal levels of norepinephrine. Interactive effects between sleep and negative affect were apparent, such that short and variable sleep were related to higher nocturnal levels of catecholamines only among individuals who were high in negative mood. These findings show that substantial intra-individual variability in sleep exists and suggest that nightly variability may represent an important avenue for future sleep research.