Closer friends have more similar actigraphy-estimated sleep patterns

Individuals in close relationships often show similarities in health lifestyle behaviors. Here, we tested associations between friendship closeness and sleep patterns in university students. We hypothesized that daily actigraphy-estimated sleep timing and duration would be more similar in closer friendships with evidence of positive covariation.

Friend pairs (n = 300; 150 pairs) wore actigraphy watches and completed daily sleep diaries for 2 weeks during the school semester. Friendships were classified as close (78 pairs) or casual (72 pairs) based on rankings completed by each friend. Daily friend-pair differences in actigraphy-estimated sleep timing (onset, offset, midpoint) and duration were calculated separately for non-school nights and school nights. Linear mixed models were used to test associations of friendship closeness (close vs. casual) with daily friend-pair differences in sleep, and to test for daily covariation of sleep in friend pairs, adjusting for covariates.

On non-school nights, friend-pair differences in sleep timing were about 30 min smaller in close friends compared with casual friends. On school nights, friend-pair differences in sleep timing were associated with dyadic differences in chronotype and class start times, but not friendship closeness. Sleep timing and duration covaried positively in close friends but not casual friends, irrespective of whether students had next-day classes.

Actigraphy-estimated sleep was more similar in university students who were close friends. Daily covariation of sleep in close friendships suggests that students influenced each other's sleep patterns. Close friendships, chronotype, and class start times play an important role in shaping social sleep behavior.