Does there exist a bidirectional association between insulin resistance and depressive symptoms in middle-aged and...

We aim to clarify the temporal relationship between insulin resistance (IR) and depressive symptoms in middle-aged and older adults, subsequently exploring the association between IR and depressive symptom trajectories.

Using data on 2,144 participants from the English Longitudinal Study of Ageing collected in 2004/05 (T1), 2008/09 (T2), and 2012/13 (T3), a two-stage analysis was conducted. First, the random intercept cross-lagged panel model (RI-CLPM) was employed to examine the temporal relationship between estimated glucose disposal rate (eGDR), a surrogate measure of IR, and depressive symptoms at both the between- and within-person levels. Second, trajectories of depressive symptoms were constructed using group-based trajectory modeling (GBTM), and the association between baseline eGDR and these trajectories was examined by multinomial logistic regression.

RI-CLPM revealed a unidirectional within-person negative lagged effect of eGDR on depressive symptoms (β_T1-T2 = -0.099, p = 0.039; β_T2-T3 = -0.133, p = 0.032). GBTM identified three depressive symptom trajectories, which were Extremely Low (n = 639, 29.8%), Low Stable (n = 1297, 60.5%), and High Stable (n = 208, 9.7%). Multinomial logistic analysis indicated that higher baseline eGDR was protective against long-term severe depressive symptoms (OR = 0.884; 95% CI, 0.798 - 0.979).

Among middle-aged and older adults, a unidirectional within-person association was observed between IR and depressive symptoms, whereby elevations in IR above an individual's usual level were associated with more severe depressive symptoms. Furthermore, lower baseline IR was associated with a reduced risk of persistent severe depressive symptoms.