Loneliness impairs daytime functioning but not sleep duration.

To assess the prospective association between daily feelings of loneliness and subsequent feelings of daytime dysfunction indicative of poor sleep quality.Three consecutive end-of-day diaries were completed by a population-based sample of 215 adults (mean age = 57.5 years, SD = 4.4). Diary questions probed sleep duration, daytime dysfunction (i.e., fatigue, low energy, sleepiness), loneliness, physical symptoms, and depressed affect experienced that day. Chronic health condition data and body mass index were also obtained. Autoregressive cross-lagged panel models were used to examine the magnitude of reciprocal prospective associations between loneliness and daytime dysfunction.Unstandardized path coefficients adjusted for race/ethnicity, sleep duration, marital status, household income, chronic health conditions, and health symptom severity.Daily variations in loneliness predicted subsequent feelings of daytime dysfunction (B = 0.16, p < .05), and daytime dysfunction predicted subsequent loneliness (B = 0.07, p < .05), adjusted for covariates. Loneliness continued to predict subsequent daytime dysfunction when depressed affect was held constant.The effect of loneliness on daytime dysfunction was independent of sleep duration, suggesting that the same amount of sleep is less salubrious when individuals feel more socially isolated.