Objective: To examine whether the prospective association between depressive symptoms and glucose metabolism is bidirectional.
Methods: We used a national sample of 4238 community-dwelling individuals 50 years or older from the English Longitudinal Study of Ageing. Participants were categorized into normoglycemic, impaired glucose metabolism (IGM), and undiagnosed and diagnosed diabetes using glycated hemoglobin and self-reported doctor diagnosis. Subthreshold and elevated depressive symptoms were defined by a score between 2 and 3 and 4 or higher, respectively, on the eight-item Center for Epidemiological Studies-Depression scale.
Results: In the age-adjusted model, categories of depressive symptoms were associated with incident undiagnosed (odds ratio [OR] = 1.54 [95% confidence interval {CI} = 0.86-2.73] and OR = 1.91 [95% CI = 1.03-3.57] for subthreshold and elevated depressive symptoms, respectively) and diagnosed diabetes (OR = 1.53 [95% CI = 0.80-2.93] and OR = 3.03 [95% CI = 1.66-5.54], respectively) for 6 years of follow-up. The latter association remained significant after adjustment for covariates. Depressive symptoms were not associated with future IGM. Diagnosed diabetes was associated with future elevated depressive symptoms in participants aged 52 to 64 years (OR = 2.17, [95% CI = 1.33-3.56]), but not those 65 years and older (OR = 0.96, [95% CI = 0.59-1.57]) for 4 years of follow-up. Adjustment for covariates partially explained this association. IGM and undiagnosed diabetes were not associated with subsequent elevated depressive symptoms.
Conclusions: These data suggest that there is a bidirectional association between depressive symptoms and diagnosed diabetes in people aged 52 to 64 years but not in people 65 years and older.