Activity patterns associated with depression symptoms in retired day and night shift workers

Objective: Evidence regarding which activity patterns relate to depression symptoms can guide the development of approaches to prevent major depression and related consequences. While prior studies have linked activity pattern disruption and depression symptoms, little is known regarding these relationships in people who were previously exposed to the circadian and sleep-wake challenge of night shift work. We therefore examined: (1) if retired night shift workers (NSWs) and retired day shift workers (DSWs) had different activity pattern characteristics; and (2) which activity pattern characteristics correlate with depression symptoms in these groups. Methods: We examined cross-sectional associations of activity patterns and depression symptoms in 64 retired NSWs (mean age = 68, standard deviation (SD) = 5) and 75 DSWs (mean age = 69, SD = 6). We used wrist actigraphy (mean days = 6.5, SD = 1.1) to measure activity levels and assessed activity patterns using non -parametric indices; and assessed depression symptoms as Center for Epidemiologic Studies-Depression Scale scores >= 8. Results: Retired NSWs and retired DSWs did not differ in activity characteristics. Depression symptoms were associated with having less activity between 13:00 h and 17:00 h in retired NSWs (Cohen's D = 1.22) but not retired DSWs (Cohen's D = 0.20). Conclusion: Activity patterns of prior NSWs may be comparable to those of prior DSW in retirement. However, uniquely in NSWs, we found that less afternoon activity was associated with depression symptoms. If persistent afternoon inactivity is confirmed as a predictor of depression risk in past NSWs, interventions targeting afternoon inactivity could be developed to prevent depression and its consequences in retired NSWs.