Loneliness and social isolation as risk factors for incident depression in type 2 diabetes mellitus: Evidence from a prospective cohort study

BackgroundThe role of loneliness and social isolation in the progression from incident type 2 diabetes mellitus (T2DM) to subsequent depression remains underexplored.Further investigation is essential to better understand how these factors influence disease progression. MethodsThis study enrolled 427,594 participants without T2DM and depression at baseline.Multistate models were employed to assess the impact of loneliness and social isolation on transitions from a healthy state to incident T2DM, then to subsequent depression, and finally to death.These associations were further examined across individuals with varying glycemic statuses, including normal glucose tolerance and prediabetes. ResultsOver a median follow-up period of 13.66 years, 14,141 incident cases of T2DM, 1,149 subsequent cases of depression, and 33,024 death events were recorded.Loneliness and social isolation were associated with elevated risks of disease progression across most transitions.For the transition from incident T2DM to subsequent depression, the loneliness group exhibited a significantly higher risk (HR=1.802,95% CI:1.521-2.135)compared to the no-loneliness group.Similarly, the most isolated group had an HR of 1.390 (95% CI:1.185-1.632)compared to the least isolated group.Additionally, participants with prediabetes faced a higher risk of developing depression following T2DM compared to those with normal glucose tolerance.Interaction analyses revealed that employment status and history of cancer modified the association between loneliness and the transition from baseline to death.