Temporal dynamics of affect, screen time, and step count in individuals at risk for mood disorders.

BACKGROUND: Identifying how affect and daily behaviors influence each other is central to understanding mood disorder development. This study investigated how negative affect (NA), positive affect (PA), physical activity, and smartphone use influence one another in daily life, and whether familial risk or mood disorder history shapes these relationships. METHODS: In a 14-day experience sampling protocol, we measured NA and PA five times a day along with passive sensing of step count and screen-on time. We examined the effect of familial high risk and history of mood disorders on within-person affect-behavior dynamics using Dynamic Structural Equation Modeling. RESULTS: The sample included offspring of parents with bipolar disorder (n = 82) and control participants (total n = 128, Mage = 37.8, 57% female), of which 32 had a history of mood disorders (recurrent: n = 3, single: n = 29). Results showed a credible bidirectional relationship between step count and PA (step count → PA: β = 0.06; 95% credibility interval [CrI], 0.02-0.09; PA → step count: β = .07; 95% CrI, 0.03-0.11), while NA exhibited no credible associations. Higher PA predicted decreased screen-on time (β = -.05; 95% CrI, -0.08 to -0.02), while increased screen-on time was associated with subsequent elevated NA (β = .03; 95% CrI, 0.01-0.06). Familial risk status and recurrent mood disorders did not alter these bidirectional effects, but were associated with lower PA and higher NA on average (all p < 0.001). CONCLUSIONS: Findings highlight PA as a key driver in the interplay between behavior and affect. Supporting PA through increased activity may help improve daily emotional experiences, even in those with elevated mood disorder risk.